weekly

Mon. Apr. 9 Wrote Bob Robinson at NSF, informing him that the Air Force seems now to be planning to dismantle and remove the UHF radars from Clear Alaska in Oct. 2001. I urged Bob to contact the commanding officer of the Air Force Space Command, General Ralph

E. Eberhart, at Peterson AFB in Colorado Springs.

week of 4-16-01

A TR shaft encoder that had been sent for repair and returned, marked "scrap" was opened for inspection. Water had entered through the ball bearing. The bearing was corroded and frozen. Several small metal posts and spacers were also severely corroded. Vertex mounted the azimuth encoders vertically with the shafts up, and provided no additional water protection. We should remount these units inside protective housings with good shaft seal. Otherwise we can expect them to fail after three or four years service.

Worked on 430 Transmitter Instruction Manual. Completed schematic diagram of the cooling system.

Prepared for reflection measurements of 430 turnstile; we are building two waveguide-to-coax transitions and a load to be added to our 3-short half-height WR2100 cal kit.

Worked at "reverse engineering" the PSR4 /5 Kollmorgen power supply used in the Vertex drives and the tie down drives. Having a schematic of this unit will help us address the frequent snubber failures in these units and will let us examine the shunt regulator (regeneration) circuitry - another problem area in the drive systems.

Week of 4-23-01

Finished drawing a schematic of the drive system's Kollmorgen regeneration circuit. Halfway finished with schematic of the soft start SCR drive circuitry.

Made measurements in the dome house to recheck the reflection from the turnstile junction. High reflection could explain the voltage breakdown suffered by the waveguide traveling collector (linear joint) during the recent test of the Gregorian transmitting setup. Very careful measurements, made with the vector network analyzer, using the 3-short waveguide cal kit, showed the input reflection loss of the turnstile's transmitter port to be 36.5 dB - essentially no reflection. The isolation between the transmitter and receiver ports was measured to be 31.1 dB. Finally, the run of half-height waveguide from the collector to the inside of the dome was well terminated on one end and then measured to have a return loss of 20 dB, a value which could subject the collector to an additional 10% in voltage. This small waveguide reflection can be tuned out, but first, the system will be tested with the new higher- power collector as soon as it is moved from the carriage house side to the dome side.

Consulted with the Ithaca lab personnel regarding the two addition new collectors under construction there.

Repaired the driver circuit for the inch worm motor driver of the new VLBA/4 terminal. The problem was an open 470k 1W resistor. The next problem to attack is a bad channel on one of the head stacks.

week of may 7, 2001

Inspected VLBA/4 head assembly. The supposed short in track 18 of headstack 1 was not found, nor was that track now shorted. No breaks were found in the signal path for track 14 of headstack 2, up to the point that can be inspected without dismantling the heads. The head assembly was reinstalled and the drive tested again. Track 18 now works, but track 14 is still dead. We will probably have to send the headstack to Signatron for repair.

Helped Phil Perillat trying to identify the interfering TV signal at 1407 MHz. This signal seems definitely to be an NTSC signal; the video carrier is surrounded by sidebands spaced by 15.8 kHz and the sound carrier is 4.5 MHz above the video carrier. The two carriers are quite unstable, drifting as much as 100 kHz in 10 minutes, so we are also looking for any strong carrier with this kind of drift (itself a mystery) that might be mixing with a tv station. Some strong local tv stations can be ruled out, because the interference has not disappeared during occasions that they have been off the air. Highest priority is to determine whether the 1407 MHz is arriving through the air or is produced here as an undesired mixing product. As of noon Thursday, Phil has just successfully detected it using a portable receiver on the platform. Direction finding can now be done.

Instructed the Ithaca lab to machine two aluminum balls, 1.5" diam and 2" diam., to fit over the end of the center post in the half-height turnstile. Modified the HFSS model of the turnstile to include the 1.5" ball and found that the match and isolation are not degraded.

Off this Friday and next Monday, Tuesday, and Wednesday, to attend Ron's graduation from Penn State.

Week of May 20 - 25, 2001

We requested and received a CD ROM compiled by Michael Wunderlich, a VLBI person at Bonn. This disk is a compilation of essentially all the available documentation for the tape recorder systems used in the VLBA, Mark III, Mark IV, and VLBA/4 terminals. Besides complete schematics, there are numerous documents containing the theory of operation of the various modules. Not all are identified by author. I suspect that several were written at Interferometrics and that none came from Signatron. I have been reviewing this CD and printing out some of the documents, adding them to the schematic-only documentation that Signtron delivered. At the same time I have been expanding a memo intended to provide a detailed description the VLBA4 system.

I have prepared a package of chip resistors to be installed on an evaluatation board with a Linear Technology 8-pole analog filter IC. This chip has the speed needed to realize Mike Sulzer's intended design; the original filter was built with 347 op amps, whose limited bandwidth caused a severe roll off in what should have been a very flat lowpass filter. Mike needs additional filters to use with the 430 dual beam system.

To: Edgar Castro

From: Jon Hagen

Date: June 1, 2001

Subject: Report for week of May 29

Monday: Memorial day holiday

Tuesday, Wednesday: Wrote paper for Single Dish Radio Astronomy Workshop, "Spectrometry and Autocorrelation".

Thursday, Friday: Worked on snubber circuit for the power transistors on the regeneration card being designed to replace the still failing cards supplied by Vertex. Contacted Paul Lane about the repair of bad VLBI recorder head. Paul asked that we remove the head stack assembly and ship it to Signatron for repair. Continued work on consolidating documentation for the VLBI system. Checked the klystron solenoids and power supplies on the 430 transmitter. An aged electrolytic in one of these supplies had blown up; all the electrolytics should be replaced in all 16 supplies.

To: Edgar Castro

From: Jon Hagen

Date: June 1, 2001

Subject: Report for week of June 4

Removed VLBI headstack assembly. Built head protector fixture and special shipping jig. Sent the assembly via overnight airfreight to Signatron, who received it the next morning. They found an open diode in the dead track (Track 14 of headstack 2) and are checking the intermittant track (Track 18 of headstack 1). We should have the assembly back here in two or three days.

Continued sleuthing the details of the Kolmorgen regeneration circuit. Bill Sisk and I will do some on- line probing to understand this circuit. New boards will be designed and built, even as they become less critical with the installation of hydraulic safety dampers.

A new failure of the Vertex pointing system once again threw us into disarray regarding the condition of our spare boards. There is a consensus that we should maintain a permanent test setup downstairs where the spare PLC and LCU computers can be run continuously. Such a set up will also aid us in maintaining the encoders, which degrade with heat and corrosion and maybe with occassional power surges.

We replaced all 32 electrolytic capacitors in the 430 transmitter magnet power supply cabinet. These capacitors, which were failing, may have been old when they were installed, only 5 or 6 years ago.

Received second new collector from Ithaca. We will install the fine tuning post here.

Week of June 10-15

Received the repaired headstack assembly from Signatron and reinstalled it in the VLBI recorder. Left the recorder, ready to be tested, to attend the week-long NAIC/NRAO Single Dish Radio Astronomy Workshop sessions. Gave a presentation "Noise Statistics and Spectral Analysis."

Received tuning post from Ithaca for fine tuning of the second new 430 MHz waveguide traveling collector.

Phil Perillat and Luis Murray followed up the Vertex problem of last week, leaving only the LCU computer as the probable culprit. They have left the spare LCU installed and running and we will resurrect our test setup to deal with the suspicious LCU.

Failure of an ac outlet on the platform left the wind speed monitor and the radar blanker out of operation.

Week of July 2

Observers have found that the the 430MHz feed in the Gregorian has an objectionable 'squint'; there is a difference of about 1/10 beamwidth in the pointing directions of the two polarizations.

Lynn Baker says that the asymmetric reflector system should not create a squint of even 1/100 beamwidth. The output of the turnstile junction is a circular waveguide, 20" in diameter. At 430 MHz, this waveguide is single-moded; the next mode, TM01, cuts off at 450MHz. The TE21 mode cuts off at 574 MHz, and the TM11 and TE01 modes at 720 MHz. The length of this waveguide, after the tip of the turnstile probe is 14.25 inches, so these modes would be attenuated by 9 dB, 25dB, and 38 dB, respectively. We can expect the TM01 mode to be present in the turnstile; it is needed to cancel the TEM mode producing isolation between opposite ports. If we decide that the -9dB leak-through of the TM01 mode should cause the squint, we can test this hypothesis be lengthening the circular waveguide. If this proves to be the fix, we will have to rearrange the transmitter waveguide installation in the Gregorian.

Received a replacement PAL device from Signatron. This was not the problem; the recorder is still unable to turn on the vacuum in the tape plenum. The D-to-A Module and the Transport Control Module were sent to Signatron to be tested in a known working recorder.

Received tuning pucks from Ithaca for fine tuning the two new collectors. Both collectors, as delivered, had a return loss of about 21 dB. The capacitive puck improved the return loss to about 27 dB. The 20dB return loss bandwidth is 4 MHz and the 15 dB return loss bandwith is 6 MHz. Collector SN002 was installed immediately in Carriage House 1. Collector SN003 will be kept in storage as a spare.

Week of July 9, 2001

Signatron received and tested our VLBA/4 D-to-A Module and Transport Control Module and found the D-to-A unit to be bad. This unit is still under warranty, so they have sent it to the vendor for repair. They say we should have it back within two weeks.

Sick 1.5 day, vac. 0.5 day

Received Lattice Semiconductor ispPac programmable filter development kit from E. Castro. These digitally reprogrammable analog filter chips should provide a fast way to implement custom low-pass, high-pass and band-pass filters at frequencies up to about 300kHz.

Worked on 430 Transmitter schematics and on trouble shooting the monoplexer control problem that burned out three 430 receiver front ends on Thursday.

Started investigation of whether TM01 feed through from the turnstile to the horn is responsible for the observed beam squint in the 430 Gregorian system.

Exchanged memos with Paul Goldsmith regarding statement and proof of the antenna theorem.

Week of July 16, 2001

Received the VME D-to-A module from Signatron, repaired under warranty by the vendor. Installed this module back into the VLBI recorder and the problem seems to be solved. The vacuum now turns on as it should and the vacuum monitor reads as it should.

Worked on design specifications for a new timing generator to replace the problematic unit built in 1983. The design goal for the new unit is that its operation be obvious and that troubleshooting be entirely straightforward. The functional description of the unit is as follows:

This unit contains a simple pulse generator for transmitter testing, klystron aging, etc. but the primary purpose of the unit is to impose safety constraints on the externally supplied timing signals used in normal operation. When these external signals (requests) violate no receiver protection, duty cycle, or pulse length constraints, they are passed on, unmodified, as commands to the transmitter. Otherwise, they are modified (pulses are cut short or suppressed entirely). Any timing violations will turn on red warning lights. These warning lights will remain lit until reset with an adjacent pushbutton. Concurrent with designing and building this unit, the transmitter's unnecessarily complicated gating and pulse interlock circuitry will be reorganized and simplified.

To: Edgar Castro

From: Jon Hagen

Date: 7-21-01

Subject: Week of 7-23-01

Monday, Tuesday: Prepared lecture for summer students:

"Electronics for Radio Astronomers". Prepared 9-page handout

for same. Delivered the (very elementary) lecture and got

the impression that the students were either unprepared or

uninterested or that they didn't find the material relevant.

Wednesday: Holiday

Thursday, Friday: Worked on design for new timing generator

for the 430 transmitter. Design is now about half done.

To: Edgar Castro

From: Jon Hagen

Date: 7-21-01

Subject: Week of 7-30-01

Thursday: vacation day (airport trip)

Rest of the week: Continued work on the design for new timing generator for the 430 transmitter. Design is now 95% done. Breadboarded the PRF limiter module to verify its operation. Mechanical design and layout will take approx. 2 days.

To: Edgar Castro

From: Jon Hagen

Date: 8-13-01

Subject: Week of Aug. 6, 2001

Monday through Thursday: Finished electrical design for new timing generator for the 430 transmitter. Now doing final drawings, mechanical design, and instruction manual. I will have Kurt Kabelac build the digital logic boards in Ithaca. The VLBI terminal suffered another hard failure; there is no communication with the MCB bus to either the recorder rack or the data acquistion rack. The MAT bus still works. Swapping the serial MCB and MAT ports on the computer showed that both ports are working. Substitution showed that the RS232/422 converter is not the problem. It seems unlikely that both racks suffered an electrical failure. We will look next at the signals on the lines.

Friday: vacation day

To: Edgar Castro

From: Jon Hagen

Date: 8-13-01

Subject: Week of Aug.13, 2001

To: Edgar Castro

From: Jon Hagen

Date: Aug. 17, 2001

Subject: Week of August 13, 2001

Troubleshooting VLBI terminal - continued: Using a storage scope on the data lines, we found that the computer was sending 3-byte commands rather than the specified 5-byte commands. Jeff Hagen then found that the initialization file in the computer had indeed become corrupted. He restored the correct file and the terminal is again working. It will be used for a run at the end of the week.

Updated schematics and put together an instruction manual for the new 100 kHz active lowpass filters used for taking incoherent scatter data from the Gregorian Dome 430 MHz radar system.

Arcing occurred at two points in the newest collector. An interior arc was almost certainly due to a sharp edge on the tuning puck between the front wheel wells. This edge will be rounded. An arc near one of the rear wheels was more puzzling, because the choke joint at the front end should elminate almost all blow by. Recently, however, plastic or wooden covers at the ends of the slotted waveguide were replaced with metal covers. These perfect shorts convert the portion of the slotted guide behind the collector into a resonant cavity. The arcing was dependent on the position of the collector, i.e. on the resonant frequency of the cavity. The metal covers should be removed before the transmitter is used again.

Wrote instruction manual - Introduction and theory of operation sections - for new 430 MHz transmitter timing generator and distributed copies to be reviewed.

Need to produce listing of current PLC program!

To: Edgar Castro

From: Jon Hagen

Date: Aug. 24, 2001

Subject: Week of August 20, 2001

At Daniel's request, wrote a section for the pamphlet being prepared for the Novemeber IEEE ceremony, designating the observatory as a milestone in electrical engineering.

Continued work on 430 MHz transmitter timing generator. Drew overall schematics showing the relation of this unit to the present two-chassis exciter and how to simplify the rats' nest of interconnections in the transmitter console and between the console and the receiver racks and the platform.

Helped in troubleshooting the failure in the the azimuth drive system that has had the telescope down the last two days. The system, when taken out of Stop mode, makes a sudden lurch that has damaged at least one servo power amplifier. While stopped, the amplifiers are active, in order to maintain a modest quiescent current in the motors - the resulting heat prevents condensation in the motors. While stopped, the integrator in the velocity loop is disabled by a small relay on one of the analog control cards. If this relay makes poor contact, circuit offset voltages will integrate up, applying maximum current to the motors. Because the brakes are on, the system remains stopped. But on start up, as soon as the brakes are released, the torqued up motors lurch forward and damage is done before the integrator gets back down to zero. This theory is being followed up now.

To: Edgar Castro

From: Jon Hagen

Date: Aug. 31, 2001

Subject: Week of August 27, 2001

Most of this week was taken up with the Vertex pointing system. We did confirm that amplifiers had been damaged after the drive currents had wrongly integrated up while the brakes were on. The integrators should have been disabled, but the sequencing apparently goes wrong when a start command comes too soon after a stop command. For now, the telescope operators are avoiding shutting down the system. Meanwhile we are digging into the PLC code in order to understand this sequencing. These investigations are hampered by lack of software documentation, but, at least, after every such incident we know more and have generated more of our own documentation for the system. We'll either get to the point of being able to maintain the system as it was built or we'll learn it well enough to do rebuild the controller with more standard hardware and a higher level programming language than the Siemens Step 5 components chosen by Vertex.

A recent VLBI trial that resulted in no fringe detection cast suspicion on our LO system. Tapasi Ghosh set the system up as it had been used and we set up the birdie generator so that one of the VLBI baseband converters would generate a 4 MHz output. We found this output to be phase-locked to our station standard. If the LO system had been bad during the run, it had subsequently been fixed or had fixed itself.

With the klystrons from the Clear Alaska BMEWS site about to be released, we must design and build or otherwise buy shipping containers for these tubes. If we supply shop drawings, the containers could be built by some fabricator in Fairbanks.

To: Edgar Castro

From: Jon Hagen

Date: Aug. 31, 2001

Subject: Week of Sept. 3, 2001 (4days)

Contacted John Cofield, Logistics Manager at the Clear, Alaska BMEWS site. Discussed the issues of obtaining, packing, and shipping the tubes. Made conceptual design for klystron shipping containers. Contacted original manufacurer of the rubber vibration mounts used in the original metal shipping containers. The original designer of the klystron crate answered my query and gave the spring rates for the two types of mounts used. I've asked them to quote prices for various quantities. I've also located a second source of these mounts.

Drafted a large block diagram of the Azimuth DCS, a large analog unit used in the Vertex pointing system. This DCS ("Drive Control System") contains the velocity loop, tachometer averaging circuitry, analog velocity and acceleration limiters, torque bias circuitry and azimuth bending compensation circuitry. The diagram allows us to relate the many control bits in the PLC program to the control options in the circuit. Editing this drawing to produce diagrams of the Gregorian Dome DCS and the Carriage DCS should require about one day each.

To: Edgar Castro

From: Jon Hagen

Date: Sept. 17, 2001

Subject: Week of Sept. 10, 2001

Sent a memo to Bob Robinson, outlining klyston storage requirments (space,humity, temerature).

430 timing control. Finished schematic/block diagrams for the Azimuth, Gregorian, and Carriage House DCS chassis (analog portions of the axis control systems). Selected accelerometer for platform vibration monitoring. Jeff Hagen will handle the computer portion of this project, using a small embedded computer accessed over the network. An identical computer with practically the same program will be embedded in the wind monitor chassis.

To: Edgar Castro

From: Jon Hagen

Date: Sept. 21, 2001

Subject: Week of Sept. 17, 2001

The failure of the VLBI tape recorder was found to caused by a shorted power transistor in one of the two reel servo amplifiers. The transistor is one of five transistors in parallel. A little investigation showed that this has been a chronic problem for some eight years, since they began running the Metrum tape drives at 320 ips, about twice the speed for which they were designed.

This speed requires nearly the full power supply voltage, leaving almost no margin for the acceleration needed in servo operation. To increase the voltage margin , 4 ohm resistors in series with each transistor to prevent current hogging and subsequent thermal runaway had been paralleled with 0.3 ohm resistors. Moreover, deceleration from 320 ips subjects the transistors to voltage and currents very close to their absolute maximum ratings. Inspection of the servo amp for the other reel showed that it had also failed and had been repaired by Signatron before delivery. I have written Hans Hinterigger at Haystack to see if there is any reason that this problem cannot be fixed by using higher voltage supplies and higher power transistors and heat sinks.

I went through the lengthy process (relearning the complicated system) of making listings of the current version of the PLC code used in the Vertex pointing system, the version produced by Klaus Wilmeroth when he came to Arecibo in March. The listings include the code, cross reference lists, symbols list, and computer-generated heirarchy chart. In addition to making hard copies, I also gave Phil Perillat diskettes containing these listings. When and if we make changes to this version, we should incrementally update the listings to avoid going through the entire process.

To: Edgar Castro

From: Jon Hagen

Date: Oct. 5, 2001

Subject: Week of Oct. 1, 2001

Received the repaired VLBI reel servo amplifier from Signatron and installed same. Signatron recommends gentle treatment, e.g. let the amplifier cool after a fast rewind before issuing a load command. This problem really deserves properly engineered solution.

Installed a single-board pc in the downstairs wind monitor chassis. Jeff Hagen programmed the pc so that wind speed and wind velocity are logged constantly and can be accessed over the net.

Worked on design of an accelerometer/single-board pc unit to take the place of the old pendulum alarm used to sense abnormal platform motion. The acceleration will be high-pass filtered prior to either square-law or linear detection so that the alarm is not triggered by normal slow platform tilts.

Inspected the tie down stations to see if the recent installation of metal roofs over the anchor blocks may have made the systems more vulnerable to lightning damage.

Continued to flow chart the PLC program in the Vertex pointing system.

To: Edgar Castro

From: Jon Hagen

Date: Oct. 12, 2001

Subject: Week of Oct. 8, 2001

Resumed work on new timing/protection unit for the 430 MHz transmitter. Added circuitry to apply receiver protection and inhibit transmitter RF in the event of low ac voltage on any of the three phases that power the transmitter. This unit will be used with a UPS. The old timing unit has never had a UPS, which likely explains why power dips often cause the transmitter to crowbar. In addition, the interlock circuitry in the receiver rack which allows the operator to disable the receiver protection (to eliminate the blanking for radio astrostronomy observations) contains some active circuitry, also not on a UPS. A UPS installed here, or a circuit modification to remove the active components) would likely prevent the receiver damage that sometimes occurs during power dips.

The new metal roofs over the tiedown blocks have changed the lightning environment by interposing a ground plane into a region that should be an equipotential region, rising and falling with the lightning voltage. Before recommending that the roof be bonded to the tie down control area rather than to ground, I plan to measure the relative conductivity of the paths to ground from the tiedown cables. These paths include the ground wire (desired path), the conductivity through the block itself (an undesired path) and whatever unexpected paths turn up. This measurement will use current transformers excited by stray ac current, if it is sufficient, or by a current of one or two amperes injected into the ground wire.

Received three evaluation boards, each containing a dual axis accelerometer (micro pendulums on a silicon chip). Tested the board and found its analog output as easy to use as its PWM output. One of these boards will be coupled to a single-board PC and installed in the Vertex shelter. It will be programmed and read out from downstairs. A detection algorithm (high-pass filter, detector, comparator) will be prepared so that the unit can furnish a Platform Motion warning bit to the Vertex System. At the same time, the unit can continue to supply a continuous stream of data for detailed analysis of platform motions.

To: Edgar Castro

From: Jon Hagen

Date: Oct. 19, 2001

Subject: Week of Oct. 15, 2001

Tape could not be loaded on the VLBI recorder because the reel motor brakes would not release due to two blown fuses. These fuses supply the reel servo amplifiers as well as the the brake circuit, so it is likely that the one of the servo amplifiers was again to blame. Nevertheless, when the fuses were changed, the unit functioned properly.

Continued work on the 430 timing/control chassis, designing an improved "logic probe" circuit for the front panel LEDs. This circuit will also be built into the final monoplexer drivers, as the printed circuit design has not yet gone out to the manufacturer. Began an additional schematic diagram for the transmitter documentation which shows the wiring of all the external devices in this system: the monoplexer drivers, receiver and LO gates, waveguide switch and interlocks, etc.

Did not work on the tiedown lightning protection problems this week but hope to return to that next week.

Spent two days interviewing six prospective technicians. Each engineer interview every candidate and there seems to be good agreement that three are not sufficiently prepared and that the others (or at least two of them) are considerably better prepared. One candidate, Ivan Cordero, was outstanding in that he gave correct answers to nearly all our technical questions.

To: Edgar Castro

From: Jon Hagen

Date: Oct. 26, 2001

Subject: Week of Oct. 22, 2001

Continued work on documentation for the 430 MHz transmitter in preparation for installation of the new timing generator.

Developed a design for klystron crates needed to transport klystrons from the Clear Air Starion in Alaska to Arecibo. The proposed design uses a steel framework nearly identical to the tilting frame in the official metal "coffin" containers. This framework, which will not tilt, holds the four rubber shock mounts. (These mounts have been ordered from the original manufacturer). Steel end frames allow the crate to be tipped to the horizontal shipping position after the tube has been loaded vertically. Three- quarter inch plywood forms a structural skin over the entire crate. Except for the large mounting ring, which must be machined, the crate is welded up from standard L-section and C-section structural steel. I hope to get help from maintenance in detailing the design.

To: Edgar Castro

From: Jon Hagen

Date: Nov. 2, 2001

Subject: Week of Oct. 29, 2001

Spent a day editing text and figures for "Spectrometry and Autocorrelation", talk given at the Single Dish Workshop, for inclusion in the printed conference report.

Continued work detailing the design for a klystron container. Faxed to Ithaca the drawing for the 24" diameter mounting ring, which must be machined from 1" steel plate. Kurt Kabelac will have one ring fabricated in Ithaca for the prototype container. He will also get prices for having a dozen rings made.

Looked at the choke joint design in the thermal transistion of the 3-4 GHz receiver. Haven't found Gene's design notes, but an analysis indicates that the choke is optimized for about 3.18 GHz, rather than for midband. We can't easily check the choke without making some waveguide adapters, but we ought to be able to "experimentally" test the device with HFSS.

Developed a design for klystron crates needed to transport klystrons from the Clear Air Starion in Alaska to Arecibo. The proposed design uses a steel framework nearly identical to the tilting frame in the official metal "coffin" containers. This framework, which will not tilt, holds the four rubber shock mounts. (These mounts have been ordered from the original manufacturer). Steel end frames allow the crate to be tipped to the horizontal shipping position after the tube has been loaded vertically. Three- quarter inch plywood forms a structural skin over the entire crate. Except for the large mounting ring, which must be machined, the crate is welded up from standard L-section and C-section structural steel. I hope to get help from maintenance in detailing the design.

To: Edgar Castro

From: Jon Hagen

Date: Nov. 9, 2001

Subject: Week of Nov. 5, 2001

Spent the week detailing the schematics and instruction manual for the new 430 MHz transmitter timing generator. These are now within two days of completion.

To: Edgar Castro

From: Jon Hagen

Date: Nov. 16, 2001

Subject: Week of Nov. 12, 2001

Spent the week completing the schematics and instruction manual for the new 430 MHz transmitter timing generator. These needed more than the two more days I estimated a week ago. They are now, however, quite complete, and have been reviewed by Bill Sisk. Another two or three days will be needed to prepare the board layout (positions of the ics on the wire-wrap board) and the mechanical layout of the chassis.

Also spent some time dealing with the klystron shipping situation. Millstone found a sufficient number of "real" crates. I had Ithaca cancel the flange ordered to make a prototype crate.z

To: Edgar Castro

From: Jon Hagen

Date: Nov. 21, 2001

Subject: 3-day Week of Nov. 19, 2001

This short week was really a continuation of last week - trying to clarify the work schedule and priorites for the Alaska klystron trip and working on the circuit board and chassis layout for the 430 MHz transmitter timing generator. This can now be turned over to the technicians for fabrication and I will turn once again to the problem of having a full complement of working Vertex spares - in particular the ever troublesome LCU computer card.

To: Edgar Castro

From: Jon Hagen

Date: Nov. 30, 2001

Subject:Week of Nov. 26,, 2001

Installed upgrade kit (5 EPROMS) in the VLBI Mark 4 formatter. Arranged for rapid payment by Cornell to Dow Elco for klystron crate shock mounts. Diana Marsh took care of this for us. The urgency then disappeared at the end of the week when the Dec. 10 trip to Alaska was postponed until at least the end of January, while the Air Force does internal paperwork authorizing the transfer of the klystrons. Finished the layout and mechanical design for the 430 MHz transmitter timing generator. It is ready for wirewrapping. Revisited the 430 MHz beam squint problem and am convinced that the TM01 mode is indeed responsible. Will make drawings for a 20" diameter extension tube to confirm this and also see how such a tube can be installed permanently, preserving the "quick change" radar/radio astronomy changeover.

To: Edgar Castro

From: Jon Hagen

Date: Dec 7, 2001

Subject:Week of Dec. 3, 2001

I spent this week working with the Vertex spare PLC, associated PC, the spare crate, and the software. These spares are again not in working condition, ready to be installed upon failure of the working units. We need to be able to diagnose these problems by ourselves (rather than by visits by Klaus Wilmeroth), and it seems that only a complete understanding of the system will let us do that. Phil keeps current with my progress and lends help when needed. This effort will likely take up most of next week as well.

To: Edgar Castro

From: Jon Hagen

Date: Dec 14 2001

Subject:Week of Dec. 10, 2001

Except for Thursday (a vacation day) I continued this working with the Vertex development system. At the week's end, I have learned to navigate through the debugging features of the system: breakpoints, dynamic memory display, interupt stack tracing, etc. I alternate between using pointing program ("lab" version, left by Klaus) and a very simple program that simply turns one of the digital i/o bits on and off and services a 1-second interrupt. While the simple program contains almost no code, it requires all the operating system "machinery" needed for the actual pointing program. It seems that, indeed, the LCU (communications CPU, a 386 pc) module is failing to establish communications with the PLC. Phil is totally familiar with the LCU software, so we should be able to combine PLC and LCU knowledge and finally get a handle on the system.

Regarding the damage of several 430 MHz amplifiers in yesterday's radar run. It would be a simple matter to install a latching monitor that would latch whenever RF power appears in the waveguide .AND. the receiver protection (monoplexer) command is not high. (This circuit could consist essentially of a single flip-flop). This would let us detect command failures to see if that is the cause of our frequent receiver burnouts.

To: Edgar Castro

From: Jon Hagen

Date: Dec 14 2001

Subject:Week of Dec. 10, 2001

Except for Thursday (a vacation day) I continued this working with the Vertex development system. At the week's end, I have learned to navigate through the debugging features of the system: breakpoints, dynamic memory display, interupt stack tracing, etc. I alternate between using pointing program ("lab" version, left by Klaus) and a very simple program that simply turns one of the digital i/o bits on and off and services a 1-second interrupt. While the simple program contains almost no code, it requires all the operating system "machinery" needed for the actual pointing program. It seems that, indeed, the LCU (communications CPU, a 386 pc) module is failing to establish communications with the PLC. Phil is totally familiar with the LCU software, so we should be able to combine PLC and LCU knowledge and finally get a handle on the system.

Regarding the damage of several 430 MHz amplifiers in yesterday's radar run. It would be a simple matter to install a latching monitor that would latch whenever RF power appears in the waveguide .AND. the receiver protection (monoplexer) command is not high. (This circuit could consist essentially of a single flip-flop). This would let us detect command failures to see if that is the cause of our frequent receiver burnouts.

To: Edgar Castro

From: Jon Hagen

Date: Jan 4, 2002

Subject: Week of Jan 2,3,4 (three days)

This week I continued to work with the Vertex software, and hope to be working with the spare hardware modules next week to get them set up as working standby units.

Stromag in Dayton OH, the manufacturer of the disk brakes used on the Kollmorgen motors, did not return my call. I have contacted them again today and will phone them every day, if necessary.

They did pass on the information that the brake disk splines are run dry (no lubricant) but the real problem is the difference between the old friction material (black) and the new material (green); the old disks lasted more than a year while the new disks wear out in a month.

The VLBI terminal has had trouble again with the reel servos, blowing fuses and overheating the servo amplifiers. Mysterious stopping, far from the ends of the tape, may be due to a defective turns counter switch on the take-up reel servo motor. Dan Smythe, at Haystack, suggested that this switch might be bouncing, producing extra pulses that made the system conclude that the reel was spinning too fast. The system, thinking that the tape was fast approaching the end of the reel, shut down the drive. A temporary fix, suggested by Dan, was to disable the switch, since end-of-reel protection is a back up to the tape position calculated from capstan rotations. So far this fix seems to be working, as a VLBI run has been underway for about two hours.

wore out in a year, while the new disks trying to find information on what lubricant, if any, should be used on the disk splines and what difference, if any, there is between the black friction material on most of the disks and the green material on the disk that just failed. I am expecting a call back from one of their engineers.

To: Edgar Castro

From: Jon Hagen

Date: Jan 11, 2002

Subject: Week of Jan 8,9,10,11 (four days)

The radar timing generator suffered its first failure since it was installed in 1986. (This failure showed up briefly, but then disappeared, about two weeks ago). Bill Sisk and Phil Perillat, using the instruction manual, quickly found the problem - a failed PAL. Bill burned a new PAL and the unit was ready for a radar run that afternoon.

I talked with engineer Jim Albright at Stromag ( 937 433 3882 ext 118). For the past four months they have been supplying the green friction material on the brake disks used in our drive system motors. Nobody else had reported trouble with the new material, but they have been completely unsatisfactory for us, lasting less than two weeks before swelling up and jamming.

Stromag quoted 3 to 4 weeks to supply 25 disks with the old material. The price was unchanged: $75/disk. The order was faxed to them.

I checked with Signatron on the cost of a spare headstack - answer: an astronomical $65,000 for the complete assembly. As an alternative, we should learn to do all the repair and alignment on our head assembly. I ordered 25 spare power transistors for the reel servo amplifiers ($2.50 each). The transistors are operated in parallel in groups of five and should be replaced as a matched set from the same production batch.

The Siemens spare rack, spare CPUs, development system computer, and monitors are being installed in a rack and will be moved from the screen room into the digital lab where access to the network and other computers will make it easier for Phil to work on the system. This will also free up the space that was expropriated in the screen room.

To: Edgar Castro

From: Jon Hagen

Date: Jan 18, 2002

Subject: Week of Jan 14,27,18 (two days vacation)

I have the PLC crate and spare boards working in the digital lab - a better set up than I had in the screen room. I seem to have learned how to get the PLC and LCU computers started together and synchronized. The Lab Test version of the PLC code runs correctly. The next steps are to test and troubleshoot the IRIG clock card and the ethernet card. Phil keeps up to date with progress on this front.

Ray Jurgens at JPL found that the person who is in charge of maintaining (modifying?) the PLC code that drives the subreflector on the 70m telescopes is:

Harlow (Hal) Ahlstrom phone 818 354 1847. ahlstrom@mail1.jpl.nasa.gov

He will be back at work next week and I will contact him to see what strategy JPL has used to deal with the PLC/LCU code written by Vertex for their system and then modified by Vertex for our pointing system.

Consulted with Tony Crespo regarding the protection circuitry of the S-band transmitter.

Gave the go-ahead to Dow Elco to ship the klystron crate shock mounts to the HIPAS Observatory in Alaska. Our crew will pick up the mounts when they go to Clear Alaska to pack the surplus klystrons for shipment to Arecibo.

To: Edgar Castro

From: Jon Hagen

Date: Jan 25, 2002

Subject: Week of Jan 21

I began working with Bill Sisk to put together at least an "interim manual" for the interim correlator. This will consist of some new block diagrams, descriptions of the digital half-band filters, and the set of schematics.

I spoke with Harlow (Hal) Ahlstrom at JPL ( phone 818 354 1847. ahlstrom@mail1.jpl.nasa.gov ) who is in charge of their Vertex control sysem. He referred me also to Bob Herroldson (760 255 8229), who is in charge of the hardware maintence of these systems at Goldstone. They have had problems with their Ethernet interface and are going to have Vertex provide a fix (first done here) at a cost of some $20k. Their problems are not unlike ours, though they have not attempted to reverse engineer thir system.

As I work with the development system, I've been able to make a much better block diagram/flow chart of the PLC software. With help from Phil on the C code in the LCU, I'm optimistic that we will succeed in mastering ("reverse engineering") the Vertex system.

To: Edgar Castro

From: Jon Hagen

Date: Feb. 1, 2002

Subject: Week of Jan 28. 2002

I put the IF/LO block diagram into a standard graphics format for Jeff Hagen, who may incorporate it into his "GUI" for system controls.

It was suspected that the VLBI recorder had a problem with the reed relay "tachometer" on the take up reel motor. But, with a scope across this switch, I observed no sign of switch bounce at any speed. The drive operated correctly with the end -of-tape sensor software turned on. The problem had been abnormal stopping. This may be an intermittent problem due to more damaged power transistors in the reel servo amplifier.

The shock absorbers for the 430 MHz klystron shipping crates have been received at the HIPAS Observatory in Alaska. We must arrange for these to be taken to the base at Clear, Alaska, even if it means one of our people driving the 100 miles from Clear to HIPAS and back. (Just an simple errand in Alaska).

I designed a torque measuring test fixture for the drive motors and amplifiers in the Vertex and tie down drive systems. The motor to be tested will be bolted to the fixture. The shaft is locked by torque provided through a beam. The bending of this beam is indicated by a pointer, just as with a standard mechanic's torque wrench. This will best both motor and amplifier since a given voltage must provide a proportional torque. I faxed the drawings to Ithaca.

Work continues on the Vertex computer system. We have learned more about the procedures needed to start the system so that the two computers synchronize before either times out. The disk drive card is now working with a working spare LCU. Next to install and troubleshoot are the IRIG time code card and the Ethernet card.

To: Edgar Castro

From: Jon Hagen

Date: Feb. 8, 2002

Subject: Week of Feb 4,2002

Drew signal flow diagrams of the upstairs IF/LO system and distributed copies. These two drawings for users and engineers have the same format as the downstairs diagrams; they contain examples of Phil's computer control syntax to allow the user to create or alter any part of the setup. Jeff Hagen is writing "GUI" menus keyed to these diagrams to make this control simpler.

In the lab test setup for the Vertex pointing control system, the IRIG time code reader is now working along with the PLC and spare LCU. The remaining and final step is to add the Ethernet card. Both Phil and Jeff are helping to advance this work, and I hope we will be ready to test the spare PLC and LCU package by the end of next week.

To: Edgar Castro

From: Jon Hagen

Date: Feb. 15, 2002

Subject: Week of Feb 11 ,2002

Received the torque measurement fixture for the motors in the pointing system and calibrated its scale. This unit was fabricated in Ithaca Beside testing the motor/amplifier combinations, this device can be used to measure the holding torque of the motor's internal brake.

Found that the 1 pps connection to the VLBI terminal was intermittent. This was easily seen by comparing the outputs from two adjacent test jacks on the front panel of the formatter, "House 1 pps" and "Formatter 1 pps" (The frequent lack of coincidence was also indicated by a front panel warning light). This problem may have been responsible for producing worthless data on a recent VLBI run.

Got the Ethernet card working in the lab test setup for the Vertex pointing control system. The difficulty in this final step was an address conflict; the LCU computer makes internal use of the port needed to configure to LAN card. Finally located instructions on how to change this default port assignment and configured two spare cards. With all the components now working in the test setup, we should formalize our maintenance strategy. I suggest the following:

We can consolidate the "lab test" versions of the PLC and LCU programs with the working versions, so no EPROMs have to be swapped after the spares pass the lab tests and so that only a single PLC program and a single LCU need to be maintained. We can also buy a Siemens utility program that will allow us to load the LCU program directly from an external PC so that the hard disk storage modules can be removed from the LCUs (eliminating any moving parts from the upstairs control computer). We will also write a maintenance manual describing all the steps needed to prepare and install the PLC and LCU programs and the sequences needed to get the PLC and LCU started and properly synchronized. Finally, we can improve the test set up. We should add an expansion box to the spare (lab) crate, as this is an important spare part we lack. (The expansion unit is more than just a chassis; it contains undocumented bus extension electronics). The test setup can contain the spare digital input, digital output, analog input, and analog output cards. All of these would be constantly exercised in the test program, producing simple blinking patterns on the indicator lamps. The test setup should also include our spare encoder interface card , hooked to a spare encoder, and also the spare PCU (portable control unit) interface card , hooked to a spare PCU. (At present we do not have a spare PCU, only a spare single-board computer that is the heart of the PCU. It would not take much to put together a complete spare PCU).

Began making block drawings of the 260/30 MHz Converter and the Visitor Romm 30 MHz IF Source Control Chassis. These will complete the series of drawings that describe the computer- controlled downstairs IF/LO system.

To: Edgar Castro

From: Jon Hagen

Date: Mar. 1, 2002

Subject: Weeks of Feb 18 and Feb. 25, 2002

Out four days sick

Completed block drawings of the 260/30 MHz Converter and the Visitor Room 30 MHz IF Source Control Chassis. Included copies of these drawings in the "do not remove" folder on the table in the control room. That folder now contains sufficient documentation for a user or engineer to configure any downstairs and/or upstairs IF/LO set up, using the computer terminal on that table.

Mechanical fabrication of the new timing generator for the 430MHz transmitter is complete. Front panel labeling is almost done. Next step is the wire wrapping.

Talked with Mike Sulzer regarding hf facility options: two transmitters vs. a single transmitter. From a cost standpoint, a single transmitter seems the obvious choice. This requires a high-power hybrid if we are to provide 0 and 90-degree feed lines for the antenna. High power branch line hybrids could be built for each of the two proposed frequencies, 5.1 and 8 MHz and switched in as needed. Additional switch gear could select right or left circular polarization and could also allow a single dummy load to function also as the hybrid's waster. The single transmitter possibility also suggests that we should investigate the use of a single feed line and a circularly polarized antenna.

This would likely restrict us to a single polarization, but Mike was ready to accept that only to minimize the number of high power switches. A single feed line would be easier to raise and lower than a dual feed line.

Worked with Edgar and Victor on the 430 MHz transmitter's crowbar circuit to find the cause of an intermittent connection.

Talked with Ganesh and Phil regarding the long-standing problems of using the cals to phase and balance the hybrids used to synthesize circular polarization. This seems to deserve a careful study and write-up.

Have been trying to get a quote from Siemens on a software produce, CPLINK, that would allow us to load the on-board silicon disk in LCU computer in the pointing system directly from an external PC. Using this software we could eliminate the hard disk units now present on our working LCU and on our spare LCU. This would improve reliability and make it easier to maintain "configuration control" with a single master copy of the program, kept and archived on the SUN.

To: Edgar Castro

From: Jon Hagen

Date: Mar. 8 2002

Subject: Week of Mar. 4 2002

Continued working with Mike Sulzer on hf facility engineering issues for the proposal he is submitting to NSF. Found an easier way to implement the baluns proposed for the bottom of the bowl: dual- frequency, rather than broad-band baluns. Found that the power splitter needed for single transmitter operation does not have to be a dual frequency hybrid or dual hybrids. Instead, a simple Wilkinson splitter, without any terminating load, can be built for the mean of the two operating frequencies. This will present the transmitter with a 1.2:1 mismatch at each operating frequency, but the proposed Continental transmitter has a built-in matching unit that can handle loads with VSWR up to 2:1.

Wrote a technical memo aimed at the problems balancing the hybrids used to synthesize circular polarization. This memo became something of a long-winded polarization tutorial but is almost complete. A companion memo will discuss the related cal issues.

To: Edgar Castro

From: Jon Hagen

Date: Mar. 15, 2002

Subject: Week of Mar. 11, 2002

Sent torque meter back to Ithaca to have the bending beam changed from 1/2" diameter to 5/8" diameter. This will increase the instrument's range from 35 ft lbs to 85 ft lbs. (The maximum continuous stall torque of the motors is 35 ft lbs, but the maximum short term torque is 70 ft lbs.)

Finished tutorial memo on measurement of circular polarization. Will distribute to the engineering staff. Now adding section on Stokes parameter measurements with the correlator and corrections to these measurements.

Haven't yet been able to get the PC Link program from Siemens. If it is unavailable, we will continue to run the pointing system with a hard disk in the PLC crate on the platform.

Tapasi reports continuing problems with Track 18 in the VLBI recorder. This problem must be investigated and fixed before VLBI runs in April.

To: Edgar Castro

From: Jon Hagen

Date: April 5, 2002

Subject: Week of April 1, 2002

Continued learning and documenting the VLBI terminal. Wrote a test procedure/training exercise that allows one to verify any data path from the IF input, through a baseband converter, the formatter, the write drivers, the monitor module, and back to the decoder (data quality analyzer). This procedure, together with a block diagram, is included in a tutorial memo,

"BBC/formatter/decoder test: using the decoder to check data from the formatter", Jon Hagen, April 4, 2002.

This memo, together with similar memos on recorder motion control and a memo on the baseband converters might provide a shortcut around the lack of a proper VLBA4 system manual.

SNAP, the VLBI terminal control language used by the field system, contains no control structures; no looping or branching. It can only execute a linear string of instructions. This makes it impossible to write diagnostic programs that will automatically exercise the equipment, looping through modes and checking for errors. I am negotiating with Jeff Hagen to have him write a simple shell that will execute the SNAP commands in an environment that does allow looping and branching. When the VLBI terminal is not in use, it could be running self tests.

To: Edgar Castro

From: Jon Hagen

Date: April 12, 2002

Subject: Week of April 8, 2002

More VLBI effort: Wrote a test procedure/training exercise to read the test tape given to us at Haystack. This is part of an effort to give us some bench mark tests to evaluate the health of our system. This tape is only a small reel and contains several minutes poor or missing data. Wrote a procedure to write our own full-sized test tape and wrote the tape.

Head 18 of Headstack 2 is still giving us a problem when writing. The headstacks must be removed for repair so, for now, we have interchanged the write cables between the two head stacks. This whould suffice for the VLBI run of April 19.

To: Edgar Castro

From: Jon Hagen

Date: April 19 2002

Subject: Week of April 15 2002

Worked with Tapasi testing the VLBI terminal in preparation for this morning's run. Had several email exchanges with other VLBI sites regarding the details of our not very documented formatter and the details of synchronizing it to our station clock. Arranged a counter to monitor the time difference between our 1 second tick and the 1 second tick regenerated by the formatter. This should be a constant since both ticks are counted down from the same (maser) master oscillator. But, during a previous experiment, the formatter time jumped and we were advised to install this monitor. No jumps occurred in today's experiment.

Showed the technicians how to shorten the elements and use the network analyzer to adjust the gamma match of a Yagi used at the visitor center for communications on 164 MHz.

Wrote a memo describing the algorithms for using the correlator to measure the Stokes parameters. This memo becomes a short appendix to an earlier tutorial memo on polarization measurements in general.

To: Edgar Castro

From: Jon Hagen

Date: May 10, 2002

Subject: Week of May 6, 2002

Got the test rack working with the spare PLC and LCU computers for the Vertex pointing system. The rack will normally be left running in the digital lab so that anyone passing by it can see at a glance that both spare computers are working properly. The monitor display is the same as the Vertex display in the control room; the time advances and the positions of the the Carriage House and the Gregorian Dome change (in the test program, the encoder positions are simulated from the time clock). If the test rack is off, it boots up running the test program when the power is turned back on, so cycling the power tests whether these computers will boot up properly when removed from the test rack and installed upstairs. Wrote a five-page memo with detailed procedures for configuring and replacing the computers in the upstairs system and in the test rack. This puts us a big step ahead in not being dependent on Vertex for emergency maintenance.

To: Edgar Castro

From: Jon Hagen

Date: May 17, 2002

Subject: Week of May 13, 2002

Worked on the VLBI recorder. Added a bracket to the back side of the recorder plate together with two large cable clamps to steady the bundle of cables attached to the head stacks. The original system was inadequate and loose; when the hinged recorder plate was swung open or closed (frequent operations) excess strain was felt by the fragile connections to the head preamp boards. Wrote and read back test tapes. Head 18, which had been failing now seems no worse than the other heads. On the other hand, the odd heads all have considerably higher parity error rates than the even heads. This didn't change when we interchanged the odd and even driver modules, so the problem must be on the odd interface boards within the head assembly.

A final step in preparing the test/storage rack for the spare pointing system computers was to provide a test of the Ethernet interface card in the LCU computer. A small program will be written to provide a one-step process to change beetween the configurations needed for the lab test program and the operational program.

To: Edgar Castro

From: Jon Hagen

Date: May 28, 2002

Subject: Week of May 20, 2002

Finished and distributed memo with procedures to test and swap the LCU and PLC computers in the Vertex pointing system. The LCU now has just one configuration option: the choice of booting and running from the silicon disk (non-volatile RAM) or from the hard disc. The silicon disk is the normal choice, while the hard disc can be a backup. During the boot process, the operator is prompted to specify if the system is to run the lab test version of the program or the operating version. The latter is the default, so that the LCU can be installed even without a keyboard.

The spare LCU and spare PLC will be taken to the platform and the swap process will be tested and practiced.

To: Edgar Castro

From: Jon Hagen

Date: May 31, 2002

Subject: Week of May 21, 2002 (four days)

Arranged to order a spare IRIG time code card for the Vertex platform system. Will add some lines of code to the lab test version of the LCU code to display the time code error counter (a counter installed two years ago by Klaus and Phil during a week-long troubleshooting marathon).

Used the motor test box built by Miguel Irizarry together with the torque tester to verify that the first motor tested with this setup produced only about 20 ft lbs or torque, far less than the rated 35 ft lbs (continuous) and 65 ft lbs (2 seconds). The next motor tested met the rated specifications and the amplifier's protective fold-back circuitry worked as it should.

Determined that the problem of bad odd-numbered tracks in the VLBI recorder is a read problem, not a write problem. Hope to find the cause of this problem next week.

Began and should finish today a memo analyzing the torques applied to the pinions and gearboxes in the elevation drives when the safety damper system uses (as built) dampers on only half the drive motors.

To: Edgar Castro

From: Jon Hagen

Date: June 7, 2002

Subject: Week of June 3, 2002 (four days)

In a successful exercise in engineering managment, I got Phil to add code to the lab test version of the LCU program to display the time code error counter (a counter by Klaus and Phil during the December '91 troubleshooting marathon). This counter accumulates the number of jumps, i.e. instances of too large a difference between consecutive time readings. The new code also displays information not recorded or even tested in the working program: number of times the IRIG card failed respond and number of times that the IRIG card was unable to lock onto the time code signal. The IRIG card installed in the spare LCU test package is passing all these tests very well, so we feel this package is ready to test on the platform.

Found that the VLBI problem of excess parity errors during reading must be a problem on the read/write interface cards deep inside the head assembly. We will have to remove the head assembly to attempt trouble shooting these cards. Meanwhile, the recorder has no problem writing, so we should be able to produce good tapes. Made several new VLBI diagrams and analysed the head preamp circuit.

To: Edgar Castro

From: Jon Hagen

Date: June 14, 2002

Subject: Week of June 10, 2002

Found a 12 kHz oscillation in VLBI read electronics which is present only on the signals from the odd- numbered read heads. The headstack must be removed to troubleshoot this problem. Since the read function is only for diagnostics, I suggest we not remove the headstack until it is necessary to fix another write problem.

Got back to working on the new manual for the 430 transmitter. Wrote theory of operation sections for the EH waveguide tuner and for the platform-mounted infinitely variable power splitter. I hope the manual and the new timing generator will both be done in about two months. This will lay the groundwork to then go through every circuit in the transmitter: replacing old capacitors, replacing several old tube modules with solid-state versions, recalibrating the entire metering system (directional couplers, power meters, high voltage, magnet, and filament metering) and straightening out all the receiver protection and interlock circuitry that has accumulated during the many years of operation.

Received a new spare IRIG time code decoder for the Vertex system and installed it in the test rack in the digital lab, where it seems to be working perfectly.

To: Edgar Castro

From: Jon Hagen

Date: June 21, 2002

Subject: Week of June 17, 2002

Redesigned the fiber optic control system for the 430 transmitter. Instead of sending identical signals to the floating (pull-up) deck and buffer (pull-down) deck, we will send each deck just the signal needed to turn it on. When the fiber to the buffer deck is out of order, the modulator will no longer suffer from "shoot through" (both decks coming on simultaneously, shorting the high voltage supply). In addition, the complicated and troublesome control card in the buffer deck will be replaced by the same simple card used in the floating deck.

The existing external control signal will still command the floating deck, but the buffer deck command will be derived from a one-shot, triggered by the falling edge of the floating deck command. The one- shot's pulse will be set at just over the modulator turn-off time, about 10 microseconds - keeping the buffer deck duty cycle within safe limits without the need to sense the mod anode voltage, as was done in the past. As an additional precaution against prevent shoot-through, the buffer deck On command will be delayed 2 us from the floating deck On command.

Designed and drew a detailed schematic for the coax-to-dual fiber circuit needed for this change.

To: Edgar Castro

From: Jon Hagen

Date: June 28, 2002

Subject: Week of June 24, 2002

Resonance in blocked-off gregorian waveguide / problem, theory & experiment

UPS installed on VLBI terminal / testing

Redesigned the fiber optic control system for the 430 transmitter. Instead of sending identical signals to the floating (pull-up) deck and buffer (pull-down) deck, we will send each deck just the signal needed to turn it on. When the fiber to the buffer deck is out of order, the modulator will no longer suffer from "shoot through" (both decks coming on simultaneously, shorting the high voltage supply). In addition, the complicated and troublesome control card in the buffer deck will be replaced by the same simple card used in the floating deck.

The existing external control signal will still command the floating deck, but the buffer deck command will be derived from a one-shot, triggered by the falling edge of the floating deck command. The one- shot's pulse will be set at just over the modulator turn-off time, about 10 microseconds - keeping the buffer deck duty cycle within safe limits without the need to sense the mod anode voltage, as was done in the past. As an additional precaution against prevent shoot-through, the buffer deck On command will be delayed 2 us from the floating deck On command.

Designed and drew a detailed schematic for the coax-to-dual fiber circuit needed for this change.

To: Edgar Castro

From: Jon Hagen

Date: June 28, 2002

Subject: Week of June 24, 2002

A 430 MHz radar experiment using only the carriage house feed was halted when it was noticed that high power was indicated in the Gregorian waveguide. It seems likely that this can happen if the Gregorian is positioned at an azimuth setting that makes its blocked off waveguide a resonant cavity. Even when the power divider is set, as it was, to steer the power only to the carriage house, a small amount of excitation at the Gregorian port could excite a large standing wave in the waveguide to the Gregorian. The fix should simply be to move the Gregorian Dome a quarter wave length (about 9 inches) from the resonant position. This can be tested on a maintenance day.

Maintenance installed a dedicated 3kW UPS for the VLBI terminal to provide uninterrupted tape motion through brief power dips and commercial power/generator change-overs.

In conjunction with the installation of the hydraulic safety dampers on the dome, Phil and I looked carefully at the motor current monitor data coming down from the Vertex drive system.

It appears that three of the eight amplifiers in the dome drive need to have their gains adjusted to make them identical to the other five for equal load sharing. This work suggests that we put together a drive system test program which can be run by the operators on maintenance days for early detection of faulty motors, amplifiers, and tachometers. The program could also test the operation of the new hydraulic damper system and the operation of the regeneration cards.

To: Edgar Castro

From: Jon Hagen

Date: July 5, 2002

Subject: Week of July 1, 2002 (3 days, after July 4 and one day doctor/lab visits)

Worked on calibration of the motor current sensors in the Vertex system. Wrote a memo containing a formula for linearizing the sense voltage-to-motor current curve. This memo also contains a set-up procedure for adjusting the scale factor ("volume control") on the amplifiers.

Assisted Alexis with the remaining wiring on the new timing control chassis for the 430 MHz Transmitter.

I believe we should install a scope monitor on the 430 transmitter in order to see just where the crowbar events occur with respect to a. the transmitter pulses, and b. power line dips. We should also fit the crowbar circuit with indicators that stay lit until reset to tell us whether any given event was triggered by excessive pulse length, excessive body current, or neither (cosmic ray shower on the crowbar thyratron?). We can also install latching monitor circuits near each monoplexer to see whether RF power exists in the waveguide at any time when the monoplexer current is low, i.e. when the receivers are unprotected. Installation of the new timing unit is the first step in resolving control failures that result in damaged receiver front ends.

Next week - July 8 through 12 - Will be at Clear Alaska with Victor Iguina and Jose' Vives, salvaging spare parts from the decommissioned Air Force BMEWs transmitter.

To: Edgar Castro

From: Jon Hagen

Date: July 18, 2002

Subject: Week of July 15, 2002 (3 days)

Alexis is installing the front and rear panel wiring on the new timing control chassis for the 430 MHz Transmitter. It should be ready for testing sometime next week.

The trip to the Clear Air Force BMEWS Station in Alaska went very smoothly, thanks again to the cooperation of Mike Smith of the Defense Dept and John Cofield, the logistics manager at Clear.

By the end of three days, we had the 20ft container filled with transmitter parts. WR2100 waveguide components included a magic T, more than a dozen straight and flex sections, and about 10 directional coupler units. Klystron accesories included four blower/duct/filter assemblies for cooling the output connection of the large klystrons, another 16 klytron tuner motors, and ten Varian vac-ion pump controllers, which we can keep connected to the recently-arrived surplus klystrons. The heaviest parts we shipped were klystron focus solenoids: two upper sections and two lower sections. We packed two driver klystrons, which we removed from their sockets in driver amplifiers, as well as the collector cooling fans and focus magnet coils for these drivers. We also got a large roll-around hi-pot tester for the klystrons; Victor had used this hi-pot tester when the klystrons were selected and packed for shipment to Arecibo.

Mike Smith will again take care of the shipping; the container should arrive at the gate in several weeks.

I believe we should install a scope monitor on the 430 transmitter in order to see just where the crowbar events occur with respect to a. the transmitter pulses, and b. power line dips. We should also fit the crowbar circuit with indicators that stay lit until reset to tell us whether any given event was triggered by excessive pulse length, excessive body current, or neither (cosmic ray shower on the crowbar thyratron?). We can also install latching monitor circuits near each monoplexer to see whether RF power exists in the waveguide at any time when the monoplexer current is low, i.e. when the receivers are unprotected. Installation of the new timing unit is the first step in resolving control failures that result in damaged receiver front ends.

Next week - July 8 through 12 - Will be at Clear Alaska with Victor Iguina and Jose' Vives, salvaging spare parts from the decommissioned Air Force BMEWs transmitter.

To: Edgar Castro

From: Jon Hagen

Date: July 18, 2002

Subject: Week of July 15, 2002 (3 days)

Alexis is installing the front and rear panel wiring on the new timing control chassis for the 430 MHz Transmitter. Itshould be ready for testing sometime next week.

The trip to the Clear Air Force BMEWS Station in Alaska went very smoothly, thanks again to the cooperation of Mike Smith of the Defense Dept. and John Cofield, the logistics manager at Clear.

By the end of three days, we had the 20 ft container filled with transmitter parts. WR2100 waveguide componentsincluded a magic T, more than a dozen straight and flex sections, and about 10 directional coupler units. Klystron accessories included four blower/duct/filter assemblies for cooling the output connection of the large klystrons, another 16 klystron tuner motors, and ten Varian vac-ion pump controllers, which we can keep connected to the recently arrived surplus klystrons. The heaviest parts we shipped were klystron focus solenoids: two upper sections

and two lower sections. We packed two driver klystrons, which we removed from their sockets in driver amplifiers, as well as the collector cooling fans and focus magnet coils for these drivers. We also got a large roll-around hi-pot tester for the klystrons; Victor had used this hi-pot tester when the klystrons were selected and packed for shipment to Arecibo. Mike Smith will again take care of the shipping; the container should arrive at the gate in several weeks.

To: Edgar Castro

From: Jon Hagen

Date: July 24, 2002

Subject: Week of July 22, 2002 (three days)

Continued work on new documentation for the 430 MHz transmitter: drawing package and comprehensive instruction manual. Hope to make the planned simplifications to the fiber optic modulator control within the next two weeks. Another worthwhile modification would be to use the waveform monitor ports on the klystron collectors to determine which klystron experienced a dip in collector current at the instant in which increased total body current caused the crow bar to fire. The collector current dip identifies the klystron that arced over internally.

To: Edgar Castro

From: Jon Hagen

Date: Aug 1, 2002

Subject: Week of July 29, 2002 (1 vacation day)

Snapshots of the klystron on display at the base headquarters in Clear, Alaska, show that the Litton Klystrons are not identical to that original Varian klystron, even though the tubes were designed to be interchangable. Nevertheless, the pictures show us how to cut viewing ports in one of our totally defective tubes to make our own display unit. The klystron at Clear had been opened with a milling machine; these days it should be easier to have maintenance cut the ports with their plasma torch.

When we simplify the fiber optic control of the 430 transmitter's high voltage modulator, we will replace the old fiber components. But it seems that the 1 mm plastic fiber is still the best choice for reliability in this short haul link where the receivers are immersed in the mineral oil of the modulator tank. The mechanical layout for the fiber transmitter box is nearly complete. Alexis Echevarria can build this box as soon as he finishes the timing control chassis.

To: Edgar Castro

From: Jon Hagen

Date: Aug 9, 2002

Subject: Week of Aug, 2002

I spent the week working on the new manual for the 430 Mhz transmitter. It will take at least two more weeks to finish this large document. While writing a section on the dummy load, explaining why we don't put sodium nitrite in the cooling system except on the rare occasions that the dummy load is needed, I found that we might as well be using the salt all the time:

To use the load, sodium nitrite, NaNO2, is added to the cooling water to produce a resistivity of about 8000 ohm cm (125 S/cm) at 57 deg C. This resistivity is quite temperature dependent; if the water temperature falls from 57 deg. C to 50 deg C (134F to 122F), the resistivity increases from 8000 ohm cm to 9000 ohm cm. It has been standard practice, over the years, to run the cooling system with only distilled water (no salt), under the assumption that any foreign substance is undesirable for the system. As a result, the power combiner's waster load, which is identical to the dummy load, has undesirably high reflectivity. However, sodium nitrite is used in Navy boilers as a rust preventative, and the concentration required here is extremely low. (Tap water in the operations building measures about 350 S/cm, more conductive than the specified salt solution). In bulk, the salt is poisonous, but the dilute solution should be quite safe. Sodium nitrite is added to sausages to preserve the red color of the meat. Less than a handfull of salt is needed in the transmitter cooling system. If we decide to maintain the proper salt solution in the system, we should determine the corresponding value of the conductivity at room temperature, to facilitate checking the concentration when the system is not running.

To: Edgar Castro

From: Jon Hagen

Date: Aug 16, 2002

Subject: Week of Aug, 12, 2002

I made steady progress with the 430 transmitter manual (really the 430 radar system manual, as it contains the details of the the platform waveguide equipment, receiver protection, and interlocks).

It would be quite easy to monitor the peak power incident on the monoplexers from the turnstiles.

We already have peak meters installed to measure the transmitter power incident on the turnstiles. Relays would allow us to switch the meters to directional couplers at the monoplexer inputs. (These couplers may already exist for cal signal injection). This monitoring would let us see at the beginning of every run that the turnstile isolation is good, i.e. that some new piece of equipment or structure on the service platform is not reflecting excessive transmitted power back up into the receiver.

Hector Monroig is putting together a third monoplexer driver to use as a spare. We also should build a third monoplexer. This might be simply a copy of one of the two (different) monoplexers we are now using, but I think we could come up with a simpler mechanical design. We might also be able to improve the electrical design for lower insertion loss.

Now that we have a supply for the PIN diodes used in the monoplexers, we should build a simple dummy load for testing lab testing the driver units. At present we use a somewhat unsatisfactory dummy load built with a high power diode.

The new fiber optic control box for the 430 transmitter's modulator is being assembled by Jesus Rios while Alexis Echevarria finishes the timing generator. When one of these tasks is finished, we can assemble the prototype circuit card to replace the transmitter's magnet current meter relays - an electronic replacement for the damaged and obsolete electro-mechanical units.

To: Edgar Castro

From: Jon Hagen

Date: Aug 23, 2002

Subject: Week of Aug, 19, 2002

The Vertex system failure of last Saturday was eventually found to be in the emergency stop interlock chain; a lightning-damaged bypass capacitor on one of the overspeed limiters. This unit, and other additional emergency stop switches, have been added to the Vertex system without the parallel status line used in the original switches. As result, the new emergency stops occur as mysterious shutdowns instead of reporting their emergency stop status. We should add the status line to the switches we have added and also update the Vertex schematics to show these switches and their locations. We also found that our set of Vertex schematics does not include the added amplifier_on/brake_release interlock circuitry. Vertex probably furnished these drawings as modified pages for the hardware manual but, if they cannot be found, we should ask Vertex for additional copies.

Swapped the LCU computer in the Vertex pointing system with the "hot spare" which had run flawlessly for several months in the test rack in the digital lab. The original LCU had not failed or misbehaved; we simply needed to verify the correctness of the swapping procedure and to verify the correct operation of the spare unit when installed in the working system. No problems were encountered. Took photos of the interior of the control system racks in order to update the Vertex drawings to include the part designation numbers.

After two days of running, the pointing system failed, indicating a problem in the LCU. We put back the original unit and returned the spare to the lab, where, as before, it ran normally. However, after one hour in the lab, it hung up and had to be rebooted. Many more hours have passed in the lab without a second failure. This leaves us once again in the position of not having a satisfactory spare LCU. We may eventually have to contract Vertex or Seimens to solve this problem.

Jesus Rios built the new fiber optic transmitter box to control the 430 MHz transmitter's modulator. The box has been tested and debugged and is ready for use. Rios is now building a prototype electronic replacement for the meter relays that monitor the klystron solenoid currents. When this is shown to be satisfactory, we will build ten units to replace all the original and now worn-out meter relays.

To: Edgar Castro

From: Jon Hagen

Date: Aug 29, 2002

Subject: Week of Aug, 26, 2002

Installed a new cpu board in the spare Vertex LCU processor. The unit seems to work perfectly in the downstairs test rack. We will try this unit on the platform next week.

Worked on the problem of lightning protection for the DACs in the tie-down stations. These units are getting their power from a dc-to-dc converter that also powers the encoders. Although the encoders have not been damaged, they may be provided the entry path to the DACs. We can

provide the DACs with power from an alternate, already available, power supply. Designed an revised circuit for the lift-off switch circuitry in the safety loop to provide high voltage isolation - again for lightning protection.

Produced a drawing of the430 MHz transmitter's oil storage and filtering system, including the proposed oil cooler. Edited the RFQ for this cooling system for submission to vendors.

Took 1.5 days vacation (Thursday afternoon and Friday).

To: Edgar Castro

From: Jon Hagen

Date: Sept 20, 2002

Subject: Week of Sept. 16, 2002

This week and the previous two weeks I have worked solidly to finish the manual for the 430 Radar System (originally to cover just the transmitter proper). The manual, about 100 pages plus a complete set of schematics, should be ready for release at the end of next week. This manual brings the transmitter's documentation up to date and up to snuff; a prerequisite to doing the same for the transmitter. We are now looking for a new transmitter engineer. I think this manual should advance his progress by about two years.

---------------

To: Edgar Castro

From: Jon Hagen

Date: Sept 27, 2002

Subject: Week of Sept. 23, 2002

I spent this week working with Ganesh on the monoplexers and their drivers. We made two modifications to the drivers. The drive pulse rise time was lengthened to reduce the switching transient induced on the receiver line. These transients, observed to be as high as several volts, may have been the cause of some receiver failures (though the drivers have been in use for two years). Slowing the rise times without inducing oscillations forced us to extend the receiver recovery out to about 40 km, so there is more work to do on the monoplexers (and the rest of the system) to reduce our minimum observable range down to the level imposed by the 2 microsecond switching time of the modulator. The other driver modification was to power the logic from a separate small 5V power supply rather than the high current supply used to forward bias the monoplexer. Switching transients on the high current supply were observed to cause occasional logic glitches.

We built a dummy monoplexer to use as a dummy load for testing the drivers. This unit uses the same type PIN diodes used in the monoplexers, and has a switch to select either 6 diodes or 8 diodes, corresponding to our 6-diode monoplexer and our 8-diode monoplexer. We plotted current vs. voltage curves for both switch settings, so that dc I-V measurements of the monoplexers will indicate shorted or open diodes.

Ganesh discovered several mechanical problems in the monoplexers which are also prime suspects for having caused receiver damage. The sliding shorts on the quarter wave bias return arms had very loose contact finger stock, allowing the bias current to be interrupted. Thicker mica stock, used to replace the insulation in the rf decooupling capacitors, resulted in inadequate isolation between the RF path and the bias input. The recently purchased PIN diodes have the same screw stud package as the original diodes, but are .030" longer. This causes them to exert excessive pressure against the fuzz button contact pads. Several diodes have been broken. This problem can be fixed by simply milling the depth of the fuzz button recesses deeper by .030". I also found that replacement fuzz buttons are available from Technit, part no. 32-01753 (.25" diam. x .125" height).

A simple calculation shows that the monoplexers should be able to stand off an incident power of 50kW cw. This is based on the following parameters:

Number of diodes at the input diode station: 4

RF resistance of each diode: 0.1 Ohms when bias current is 0.5A

Average power dissipation rating of stud-mounted diode: 25W.

We do not exceed a 6% duty cycle, so the monoplexers should withstand 800 kW, which corresponds to turnstile isolation of only -5 dB with a transmitter power of 2.5MW. (I still recommend that we arrange to monitor the power incident on the monoplexers).

To: Edgar Castro

From: Jon Hagen

Date: Oct. 4, 2002

Subject: Week of Sept. 30, 2002

The repaired monoplexer drivers and monoplexer were re-installed and an ionosphere run has been in progress this week, so far without receiver problems. I designed a simple circuit to be added to the drivers to provide their high voltage power supply with short circuit protection. (At least one monoplexer has shorted, resulting in a burned resistor in its driver). The low voltage supplies have built-in short circuit protection, so with this addition, the drivers will be totally short circuit proof.

The prototype magnet current metering circuit has been built and debugged. Hector Monroig it putting it into a box, together with a small power supply. This unit will be placed on top of the transmitter console and connected in parallel with one of the still-working meters. When we have decided that it is reliable (not damaged by power glitches, lightning, etc), we will design a small circuit board and built 16 of these units to replace all the defective and obsolete meter relays.

I finished the manual for the 430 MHz Radar System. Mike Sulzer and Sixto have a copy and have pointed out a few typos. Once the new timing system is installed I'll go over the manual once more and distribute multiple copies.

Wednesday: family medical (all day for an appointment in San Juan)

To: Edgar Castro

From: Jon Hagen

Date: Oct. 11, 2002

Subject: Week of Oct. 7, 2002

The ionospheric run this week was interupped from three or four hours when the two monoplexers failed simultaneously at 6am, Thursday morning. Both were found to have shorted diodes in their input stations. The receivers and monoplexer drivers were found to be undamaged.

This simultaneous failure strongly indicates a failure of the control system; the "receiver protect" going down or simply missing when the transmitter is producing RF. The diodes were replaced and the run continued for another full day without problems.

I have begun debugging the new simpler pulse control chassis, which contains both safeguards against timing errors and latched failure indicators. The present 20 year oldand

repaired monoplexer drivers and monoplexer were re-installed and an ionosphere run has been in progress this week, so far without receiver problems. I designed a simple circuit to be added to the drivers to provide their high voltage power supply with short circuit protection. (At least one monoplexer has shorted, resulting in a burned resistor in its driver). The low voltage supplies have built-in short circuit protection, so with this addition, the drivers will be totally short circuit proof.

The prototype magnet current metering circuit has been built and debugged. Hector Monroig it putting it into a box, together with a small power supply. This unit will be placed on top of the transmitter console and connected in parallel with one of the still-working meters. When we have decided that it is reliable (not damaged by power glitches, lightning, etc), we will design a small circuit board and built 16 of these units to replace all the defective and obsolete meter relays.

I finished the manual for the 430 MHz Radar System. Mike Sulzer and Sixto have a copy and have pointed out a few typos. Once the new timing system is installed I'll go over the manual once more and distribute multiple copies.

Wednesday: family medical (all day for an appointment in San Juan)

To: Edgar Castro

From: Jon Hagen

Date: Oct. 18 2002

Subject: Week of Oct. 15, 2002

Monday morning Luis Murray noticed that the LCU pointing computer in the platform equipment shelter had its red "fault" light lit. According to the Siemens manual, this indicates a CPU failure detected by a boot time diagnostic routine - "contact your Siemens representative". We attempted to reboot this computer ( LCU #1) to avail; it would not come up running the operating program. We did get it to boot up in our laboratory test rack, but the "fault" light remain lit and the unit would not synchronize with the PLC, its co-processor. We installed our only spare LCU (#4) at the platform and it has been running all week.. (Yet LCU #3 was installed under similar circumstances about two months ago and failed after three days). We have sent LCU#1 and LCU#3, which was a replacement for the never satisfactory LCU#2, to Siemens for repair. They quoted four weeks turnaround. During this period, we will again be without a spare. This board is absolutely vital for our pointing system. It is built by Siemens for their proprietary control rack and there are no second sources.

I continued checking out the new 430 transmitter timing generator, section by section, fixing wiring and some logic mistakes. The unit is now fully functional, ready to be connected in parallel with the old generator as a diagnostic tool, to see that the computer-generated timing sequences are indeed within limits. The complete installation of the new generator will probably require a full week while we straighten out and document decades of timing and interlock modifications.

To: Edgar Castro

From: Jon Hagen

Date: Oct. 25, 2002

Subject: Week of Oct. 21, 2002

We are trying to buy a new spare LCU , one of two CPUs in the Vertex pointing system, in order to have a spare while Siemens repairs our failed units. Our local Siemens rep, Felix Encarnacion at Prime Controls, referred us to the Siemens office in Tennessee to check part numbers and availability. I spoke with Tony Sizemore in that office, who told me that the CP581 is now a discontinued product, even the last version, which came out in 1997, and that we may not be able to buy any version of the CP581. This is bad news; we had expected that as new versions of the Pentium chip are introduced, Siemens would continue to produce new versions of their CP581. Sizemore also was doubtful that Siemens would repair our failed units. He is going to trace the units we submitted for repair and also see if there may be a CP581 available from Germany, as none remain in stock in the U.S. He said that the Siemens S5 system, while now 30 years old, is still a current product, and mentioned several current network interface units that might be made to substitute for the CP581 - although he doesn't know that our CP581 does quite a bit of processing.

I added a circuit to the new 430 transmitter timing generator to detect faults in the monoplexer command/acknowledge loop from the transmitter to the platform. Even a momentary fault in this communications loop will cut off the pulse in progress and light a latched indicator lamp.

We have begun the installation of the simplified fiber optic control for the buffer deck of the modulator.

To: Edgar Castro

From: Jon Hagen

Date: Nov. 1, 2002

Subject: Week of Oct. 28, 2002

We are ordering two CP581 computer boards from Siemens for the Vertex pointing system so that we will again have a spare. (Our previous spare was installed on the platform two weeks ago when the working CP581 failed). While Siemens has discontinued this product, there were still a few units in stock in Germany - although they haven't found any "on board silicon disk" chips. We can run with the standard disk drive, but we would prefer the silicon disk, for reliability (no moving parts). I located a Danish company that makes a 'CP586' board, designed to be compatible to the Siemens CP581. The availability of such second source hardware may be the key to keeping the pointing control system in operation. Our system works well, and the design and installation of a replacement system is beyond our present means, probably requiring some two or three man years of engineering work.

The new timing generator is ready for installation and its documentation is complete. I have set it aside until we have a break in 430 operations after the next long campaign.

I am now working on the VLBI recorder, which has two heads that have trouble writing when the tape speed is 160 ips.

To: Edgar Castro

From: Jon Hagen

Date: Nov. 8, 2002

Subject: Week of Nov. 4, 2002

I have spent this week working on the VLBI recorder. The problem with head 18 turned out to be on a Write Driver card. This problem could be diagnosed in "bypass" mode, without running the tape drive. We have swapped the this card with the card from the other headstack, which has us up and running for the runs this month. I'm optimistic that we can troubleshoot the defective card - not nearly as difficult as problems in head assembly. I wrote a new full-length test tape and edited my memos on how to write and read that tape, and how to test the data paths through the DAS and the recorder. I also have been making block diagrams of the system.

To: Edgar Castro

From: Jon Hagen

Date: Nov. 15, 2002

Subject: Week of Nov. 11, 2002

Continued working with the on the VLBI recorder.

Attended the Gordon Lecture and the informal lecture on the following day.

Prepared a recruiting talk and delivered it in Mayaguez yesterday to an audience of about 40 electrical engineering students. Three of them, who will graduate next month, handed me their resumes on the spot. Another resume arrived by email this morning. Prof. Rafael Rodríquez Solís highly recommended a recent graduate, Snaider Rodríquez, now teaching in Aguadilla. I have e-mailed him, hoping we can interview him next week, along with three other recent graduates, already scheduled to be interviewed.

To: Edgar Castro

From: Jon Hagen

Date: Nov. 22, 2002

Subject: Week of Nov. 18, 2002

Found and fixed the write problem on the VLBI recorder. The signal channel for Head 18 of Headstack 1 had a capacitor making an intermittant contact in its DIP socket.

Interviewed four candidates for engineering jobs. Felt that these time-consuming interviews were unsatisfactory, in that we were not able to judge sufficiently the candidate's mastery of basic engineering fundamentals. We need a better interviewing process and a more formal way to test applicants. Prepared a six-problem written quiz with the idea of sending to applicants when they first submit their resumes. We would tell them that we are looking for candidates who would do quite well on this quiz, and invite them work the problems and submit their solutions to us. Poorly prepared applicants would not respond. Showed this test and a draft of a cover letter to our HR department head, Rey Medina, who flatly turned down the idea, saying it would be clearly illegal and leave us open to prosecution. If we are not able to administer any type of test, we will have to hire only experienced people, people we already know, or engineers who have already passed both parts of the professional engineering exam.

To: Edgar Castro

From: Jon Hagen

Date: Dec 6, 2002

Subject: Weeks of Nov. 25 and Dec. 2, 2002

Week of Nov. 25, 2002: Vacation

Week of Dec. 2, 2002: Monday: Vacation. At the ALFA teleconference on Tuesday, two technical issues were resolved. The amplifier stability question was put to rest as the Australians had put a sliding short on the output terminal of a cooled prototype amplifier and found it to be stable. The encoder problem was resolved when they found that Kollmorgen can supply the gearhead motor with an internal absolute multi-turn encoder. This allows them to rotate the receiver with a single pinion gear, whereas an external gear-driven encoder, would have necessitated a drive system with two motors, torque biased to remove backlash. They're also now happy to install a hard final stop, as they verified that the motor drive amplifier has fold-back protection against overload.

Added two questions to the proposed test for engineering job applicants and wrote a solutions sheet. Converted both the text and the solutions to PDF format. I think will find a way to use this test (or other tests) without violating any labor laws. Candidates who not passed part two of the professional engineering examination are classified as "engineers in training." They cannot use the title "engineer" until that have passed that exam. Thus, the government of Puerto does not consider a BSEE diploma to be an adequate certificate of technical competence.

Given that we have several positions to fill, and given the further staff turnover expected in the next two to three years, I hope we can develop a systematic, fair, and successful recruiting strategy.

To: Edgar Castro

From: Jon Hagen

Date: Dec 6, 2002

Subject: Week of Dec. 9, 2002

Assisted Victor Iguina and Hector Monroig installing the new fiber optic modulator control unit for the 430 Mhz transmitter. This installation should be finished next week. The next task will be the installation of the new timing unit, which has been running continuously on the bench.

Began making block drawing of the Gregorian receivers. These diagrams will complement the set of IF/LO block diagrams, showing signal paths and showing the software commands needed to set all the switches, attenuators, frequencies, cals, shutters, etc.

Wrote a simple spread sheet program for the ALFA receiver to confirm gain/noise/dynamic range calculations. Present design looks fine to me; dynamic range can be extended at little S:N cost; increasing the headroom before 1 dB compression from 11 to 32 dB would raise the system temperature only about .4K.

Sent the Ithaca lab the drawings for the remaining parts to be built for the new monoplexer.

They will machine all the parts, but the critical center section will assembled here, after RF testing.

Went through the pile of applications received from our recent help wanted ad. Hope to help organize the follow up effort next week.

To: Edgar Castro

From: Jon Hagen

Date: Dec 23, 2002

Subject: Week of Dec. 16, 2002

Finished installation of the new fiber optic modulator control unit for the 430 Mhz transmitter. The floating deck and buffer deck are now totally decoupled, eliminating a troublesome section of control circuitry, and making it easier to trouble-shoot the modulator.

The prototype klystron magnet current meter circuit was installed. As soon as this is deemed reliable, we will build 16 of these units to replace the defective meter relays.

To: Edgar Castro

From: Jon Hagen

Date: January 3, 2003

Subject: Week of Dec. 30, 2002 (including one sick day and one New Year's day)

Drew schematic diagrams for the 430 transmitter's receiver interlock circuitry - Y switch, Jennings switches, control room "Ant/Load" switches etc. Added this diagram to the new 430 radar system manual. With Victor Iguina, changed the Y switch interlock to be part of the regular transmitter interlock chain, rather than a special part of the High Voltage control circuitry (where it had been installed originally in 1966 to avoid making connections in a hard-to-reach part of the console).

Straightening out and documenting all the external interlock circuitry is part of the preparation for installing the new timing generator.

To: Edgar Castro

From: Jon Hagen

Date: Jan. 10, 2003

Subject: Week of Jan. 3, 2003

With Victor, continued cleaning up the transmitter console, removing old modifications, and generally bringing the transmitter into agreement with the new documentation. Asked Litton for information on the 5573 klystrons - all we had was two pages of a 15-page test procedure. They responded, sending us the complete document plus three memos: the tuning procedure, body current reduction procedures, and filament current adjustment procedures. They indicated that they might be able to pull more information from their files.

Am awaiting the go-ahead to send out technical quiz to about fifteen prospective engineers.

Studied the proposed designs for the ALFA rotation drive and control/monitoring system.. We need more information on the former; the latter seems ready to sign off on. I suggested that the cable wrap 'snake' ride on a sheet of UHMW (Ultra High Molecular Weight Polyethylene, a.k.a. "poor man's Teflon") . This material is recommended as a tough anti-friction material for conveyor applications, and should be better in this application than stainless steel.

Assisted on Sunday in trouble-shooting the 430 system. The monoplexer drive cable to the platform was found shorted (and water logged).

To: Edgar Castro

From: Jon Hagen

Date: Jan. 17, 2003

Subject: Week of Jan. 13, 2003 (one vacation day)

Designed a replacement for the dual-channel reflected power alarm/shut-down chassis in the 430 transmitter. The old unit uses vacuum tubes, obsolete Schockley diodes, and a heavy external regulated power supply (that also uses tubes). The new unit will use ics and a small internal power supply. The design is fully detailed, documented, and ready to be given to one of our technicians for construction. Once this unit is installed, the transmitter console will be less crowded and will finally be free of vacuum tubes.

To: Edgar Castro

From: Jon Hagen

Date: Jan. 27, 2003

Subject: Week of Jan. 20, 2003 (one medical day)

Ordered 20 new panel meters to replace the worn out magnet current meters in the 430 MHz transmitter console. Revised the circuit design for the electronics that will be added to each of these meters to perform the meter relay function (tripping off the high voltage interlock chain if one or more magnet currents fall below their thresholds). This circuitry will now include a latched LED to indicate which magnet failed, even if the failure was momentary. A printed circuit board will be designed for these circuits.

The new reflected power alarm circuit is under construction.

The new timing generator was mounted in the console and connected in parallel with the old generator. It confirmed that the pulse sequences from the SPS do not violate its timing restrictions. This new generator will fully installed during the upcoming shut down period.

To: Edgar Castro

From: Jon Hagen

Date: Jan. Feb. 3, 2003

Subject: Week of Jan.27,20

The new timing 430 MHz transmitter generator ran in parallel with the old generator during a one day run. This uncovered one oversight in the design, which was fixed with a connection to a previously unused OR gate input. Next week we will make the change over to the new unit and remove the old unit.

The circuitry for the new reflected power alarm circuit has been built and is being tested in the lab. It will be installed, and the old unit removed, during the upcoming shutdown period.

Monday was mostly spent in a team effort to fix a failure in the azimuth drive system. Two new Siemens single-board PCs were received as spares for the pointing system. One is already being configured in the lab.

We spent more evaluating prospective engineers and recommended hiring Calixto Rodríquez and Giacomo Comes. I recommend that we hire a fresh graduate from Mayaguez to train as a transmitter engineer.

To: Edgar Castro

From: Jon Hagen

Date: Jan. Feb. 12 2003

Subject: Week of Feb. 3, 2003

An additional circuit board was designed for the 430 MHz transmitter's new reflected power alarm chassis. The new board adds the arc detection/latch/shut-off circuitry. The new chassis will replace both the old Reflected Power Alarm Chassis and the "Fast RF Shutoff Unit", another chassis inside the console. This change will also replace confusing alarm/reset functions on the front panels of the console- mounted "Low Level Amplifier" and "Low Level Gating" chassis. New front panels will be made for these two units, eliminating the various alarm and reset functions, as well as several confusing and now unused modulation control switches.

The never-used automatic high-voltage control circuitry for the Inductrol was removed, bringing that part of the console circuitry back to conformity with the schematic diagrams. The complete documentation for the transmitter - schematics and manual (operation, maintenance, theory) is totally up to date.

The timing generator change-over should be finished next week, and the old unit removed from the console. Remaining transmitter maintenance projects include overhaul and modernization of the crowbar circuitry, rebuilding of the bleeder tower (which catches fire about once a year), installation of the new oil cooler, and operational tests of the newly acquired L-5773 klystrons.

To: Edgar Castro

From: Jon Hagen

Date: Feb. 18, 2003

Subject: Week of Feb. 10, 2003 (one day out for medical appointment in San Juan).

The arc detector circuitry was added to the new reflected power alarm chassis. This chassis is ready for installation in the console to replace the old vacuum tube unit.

The old timing generator was removed and the new generator installed. Slight modifications had to be made to the low level modulator chassis. The documentation for these changes, and the installation of the new timing generator is current. The console is being cleaned up in general: dozens of unused cables and wires removed, remaining cables labeled, unused front panel controls removed, and remaining controls being relabeled, where necessary.

The sixteen new ammeters for the klystron magnet current arrived and will be installed as soon as possible.

To: Edgar Castro

From: Jon Hagen

Date: Feb. 26, 2003

Subject: Week of Feb. 17, 2003

Like the reflected power shut-off unit, the klystron arc detectors in the 430 transmitter were found to be non-operational. The two arc detector chassis and the six detector heads are being repaired in the lab. The new arc/reflected power shut down chassis will be installed at the same time the arc detectors are reinstalled. Some of the arc detector photo diodes are bad. These 1N2175 diodes may be impossible to find. If necessary, we can replace them with inexpensive HP Versalink plastic optical fibers and recevers. (The photo sensor has to fit into a long small diameter hole - a waveguide beyond cutoff that will not leak RF or be influenced by RF).

The installation of the new timing generator is complete. Cables have been labeled and the console oscilloscope source selector switch has been relabeled to correspond to the new timing signal definitions.

I found a 2002 article by Bill North et al describing a modern replacement for an old crowbar driver at the MIT Bates Linear Accelerator. Their crowbar and old driver are identical to our units. Their new driver eliminates the large hydrogen thyratron and associated vacuum tubes. The thyratron is replaced by a passive triggered spark gap - a miniature version of the crowbar itself. Advantages of this all solid- state driver are the elimination of expensive, obsolete tubes and the elimination of the thyratron's proclivity to fire spontaneously - a trait that gets worse with age. The parts count for this circuit is small and, except for the triggered spark gap and a small pulse transformer, our present driver contains the necessary parts for it to be rearranged into this more modern circuit.

To: Edgar Castro

From: Jon Hagen

Date: Mar. 4, 2003

Subject: Week of Feb. 24, 2003

Kurt Kabelac at the Ithaca Lab found a distributor on Long Island who has twenty-two 1N2175 photo- diodes. These will allow us to repair the arc detectors in the 430 MHz transmitter to as-built condition and will give us a good supply of spare diodes.

The new timing generator has been running with no problems so far.

I "reverse engineered" the fiber optic receiver unit designed by Bill North for the BMEWS transmitter modulator control. (We brought back several of these units from Alaska. They should be usable in both decks of our modulator with essentially no modifications. This saves us laying out a printed circuit to replace the prototype boards now operating in our transmitter.

Prepared a presentation for the AUSAC on recent improvements to the 430 transmitter.

To: Edgar Castro

From: Jon Hagen

Date: Mar. 7, 2003

Subject: Week of March 3, 2003

Contacted the MIT Bates Accelerator laboratory. They supplied the make and model of the triggered spark gap used in their modernized crowbar driver. They offered to furnish us complete information so that we can essentially duplicate the high power part their unit. We plan to put together an all-new crowbar unit to replace the aging, messy, and somewhat improvised original unit. (It was redesigned and rebuilt on site during the installation when the original design proved prone to false firing). Bill North works there one day a week; we can reach him there by phone on Wednesdays. Besides building a new driver, we may make some slight modifications to the main spark gap of our crowbar to ensure that it can fire throughout the entire range of the high voltage supply.

The Ithaca lab has finished the parts for the new monoplexer and is shipping it to Arecibo, together with the custom-made mica insulators. We will do the final assembly and tuning here. They will also ship down the recently received replacement diodes for the arc detectors in the 430 MHz transmitter. (The shipment just arrived).

Submitted sketches to the Maintenance Department for a klystron lifting frame to be installed in the klystron storage building in the old staging area. This frame will allow us to lift the klystrons high enough to set them into their dollies for vertical storage in this building.

To: Edgar Castro

From: Jon Hagen

Date: Mar. 17, 2003

Subject: Week of March 10, 2003 (included 3 sick days)

Worked with Victor Iguina on the display klystron. The tube, selected earlier for this purpose, was taken to the machine shop and the display window locations were marked in chalk. Melvin Cortes used the plasma cutter to open these windows in the stainless steel body of the klystron. A high pressure water cleaning will be used to remove the spattered steel and copper.

If the tube is to be displayed in an upright position, it can be placed on one of the dollies. For horizontal display (better), saw horse style legs can be welded to the body.

The replacement diodes are being installed in the 430 transmitter arc detectors.

To: Edgar Castro

From: Jon Hagen

Date: Mar. 28, 2003

Subject: Weeks of March 17 amd 24, 2003

Finished replacing the photo-diodes in the six Arecibo detectors of the 430 MHz transmitter. The units were actually rebuilt with new transistors as well as the new photo-diodes. All have been tested are and are ready to be re-installed.

Checked out the recently completed reflected power meter for the 430 transmitter. Found and fixed several wiring mistakes and design mistakes. This unit is now ready for installation and its documentation is complete.

Began reviewing Fourier transform spectroscopy to collaborate with Bill Sisk and Desh on ALPHA back ends.

Inspected the recently assembled spare LCU processor package for the Vertex pointing system. Luis Murray did the mechanical work while Jorge Rodríquez installed the software. The unit is in the test rack in the digital lab, running the Lab Test version of its program. Everything looks correct, though we will also test it at the platform in the actual system. Luis is now putting together a second package, so that we will have two spare processors. This processor is the only component in the Vertex system that has given us continuing problems. As it is now no longer available, we feel we must have two spares.

To: Edgar Castro

From: Jon Hagen

Date: Apr. 4, 2003

Subject: Week of March 31, 2003

I met with Tony Crespo to discuss the problems with the S-band transmitter's magnet current regulators. The basic problem seems to be with the current control loop. The regulation is not sufficiently tight, requiring the operator to readjust the current whenever the magnet temperature has changed appreciably. The electromechanical system (motor-driven gang of three Variacs) seems to have adequate precision, i.e., the voltage steps between adjacent turns of the Variac winding are small enough. The system does not need to be fast; at the most, adjustments might be needed every half minute. Therefore the bandwidth of the servo system can be made very low, so that backlash in the drive gear and pinion and inertia will not limit the accuracy. One way to lower the bandwidth is simply to increase the gear ratio between the motor and the Variac. The Variacs for the two magnets are different models and have different ratios; one is about 2:1 and the other is about 1:1. These could both be increased to at least 8:1. This would likely fix the problem. Alternatively, we could modify the controllers to reduce the duty cycle of their output pulses and thereby lower the motor speeds. We have the schematic diagram for the controller, so it is by no means a black box. I have redrawn it to make its operation more obvious. Once the bandwidth has been lowered, by changing the gears or by modifying the controllers, the controllers' gain controls can be moved to higher settings in order to decrease the servo error to an acceptable value.

Superior Electric, the manufacturer of the Variacs (Powerstats), provides the motorized versions in speeds of 5, 15, 30 and 60 seconds for full travel. Ours seem to be the fastest. We can probably buy the gears from Superior to convert them to 60 seconds for full travel.

A second improvement could also be made, if necessary. Continental Electronics derived the loop feedback signal from a current transformer at the output of one of the Variacs, so they are actually regulating the ac current in one phase of the three-phase input to the rectifier/filter magnet supply. A more direct feedback method would be to sample directly the magnet's dc current. This would have required only a trivial modification to the controllers. However it would also have required either the installation of Wye-to-Delta isolation transformers (to allow grounding one ends of the magnets), or a high common mode differential measurement circuits (to measure the voltage across floating shunt resistors).

I suggest we first increase the gear ratio to lower the loop bandwidth, allowing greater precision. If we find that the required accuracy requires direct dc feedback of the magnet current, we can then address the isolation problem.

I continued to discuss the ALFA back-end considerations with Bill Sisk. We are reviewing polyphase DFT filter bank architectures - and other multi-bit schemes for better resistance to RFI.

Victor installed the new Reflected Power Alarm/Shut-off chassis in the 430 MHz transmitter console and removed the now obsolete Fast RF Shut-off unit.

To: Edgar Castro

From: Jon Hagen

Date: Apr. 11, 2003

Subject: Week of April 7, 2003

We are ordering the parts to lower the speed of both of the S-band transmitter's motorized Variacs which power the dc magnet supplies. Running these at a lower speed will allow the control system to maintain the magnet currents more precisely. Including the spare Variacs, we have three different models, but the necessary parts are be available for all three.

Victor Iguina installed one of our Litton L5773 klystrons in the 430 Mhz transmitter and successfully tested it up to nominal full power, 1.25 MW. For this test, the transmitter was configured to run with a single klystron. Victor encountered no problems with the tube's vacuum nor with high voltage or RF conditioning and had the tube operating at full power within a couple of hours after completing the installation. The L5773 is one of the high efficiency klystrons obtained recently as surplus from the BMEWS radar station in Clear Alaska.

I have studied the operation of the polyphase DFT filter bank algorithm and am writing a tutorial memo. Bill Sisk and I will expand our informal ALFA back-end discussions to form a design group including also Avinash Deshpande, Phil Perillat, and Giacomo Comes.

To: Edgar Castro

From: Jon Hagen

Date: Apr. 17, 2003

Subject: Week of April 14, 2003 (4 days)

After successfully testing the Litton L5773 klystron in the 430 Mhz transmitter, Victor Iguina turned his attention to a long-standing problem with the magnet for the other klystron. Bob Zimmerman had decided about five years ago that this magnet had an internal short, and had put an isolation transformer on its power supply. Victor found the problem to be in a multi-pin connector. The pin for one winding had overheated, increased in resistance and had also established path to ground - although of very high resistance. The magnet itself seems to be in good condition. While we have a spare magnet, we were happy not to have to install it, as the cooling water connections are submerged in the oil tank and any water leakage from these connections would contaminate the oil.

I finished writing a 5-page tutorial memo on the polyphase DFT filter bank algorithm and also helped Desh put together a memo outlining the requirements for the ALFA back end processors.

To: Edgar Castro

From: Jon Hagen

Date: Apr. 25, 2003

Subject: Week of April 21, 2003

Victor removed the successfully tested L5773 klystron and put the old L3403 back into the socket, after fixing the magnet connector problem.

I spent most of the week writing two technical memos. The first, for Lynn Baker and Jagadheep is the microwave theory involved in the design of the choke joint for a thermal transition in circular waveguide. They had built the thermal transition for the new 6-8 GHz by scaling an old design done by Gene Lauria, and saw a passband feature that led them to look into the choke joint design. I had originally coached Gene on that design but apparently I had never written it up.

The second memo was in response to a measurement done early this week by Phil and Lisa and written up by Phil on his web page. The Downstairs IF/LO System has several 8-way amplifier units, allowing several back-ends to be left connected, whether or not more than one back-end is in use at any time. In each unit, one of the eight outputs feeds a front panel monitor port, which is often left unterminated. The other seven ports feed rear panel connectors, which are terminated by back-end processors or by 50- Ohm loads. They noticed that the base line ripple, as measured by back-end processors was considerably worse when the front panel monitor port was left unterminated, even though there was an isolation amplifier between the splitter output and this front panel port. They replaced this amplifier with a higher gain amplifier embedded between two attenuators. The reduction in the ripple (in dB) was half what they expected. The memo explains their observation in a fairly tutorial (long-winded) fashion.

Both of these memos distracted me from the problem of back-end spectrum analysis for Alfa, but I am now back on that again.

To: Edgar Castro

From: Jon Hagen

Date: Apr. May 2, 2003

Subject: Week of April 28, 2003

I spent some time planning improvements we can make to the 430 MHz monoplexers and drivers. At present, the eight diodes in each monoplexer are paralled, with a 2.7 Ohm resistor in series with each diode for current equalization. A single line supplies current from the driver circuitry. Since we have had numerous diode failures, and since diode failures are prone to cascade, we might better supply each diode's drive current individually, using an 8-conductor cable between the driver and the monoplexer. The driver would monitor the current flowing in each diode; the handshaking "acknowledge" pulse would be inhibited more accurately when even one diode's current is outside the allowable range.

Most of the week was spent on considerations of the back-end processing for Alfa. This was complemented by an invitation to review a proposal for a large back end processor system.

To: Edgar Castro

From: Jon Hagen

Date: May 9, 2003

Subject: Week of April 5, 2003

Again, most of the week was spent on considerations of the back-end processing for Alfa. A meeting was held May 8, attended by Bill Sisk, Phil Perillat, Jeff Hagen, Giacomo Comes, and Jon Hagen. Don Backer talked about the Berkeley "F Board", the spectrum analyzer engine for the ATA's FX correlator.

I designed a bolt-on steel leg arrangement for the display klystron. Jose Vives should be able to fabricate this in our Electronics machine shop. If not, it can be made in the maintenance shop.

Kurt Kabelac got me involved in his talks with injection molding companies to procure the 40,000 plastic grease retainers needed to protect the bottoms of the reflector adjusting screws. An idea came up for a simpler design, which should be less expensive to produce. I discussed this design briefly with Jose' Maldonado today (Friday). We will meet next week.

The Perkin Elmer vacuum spark gap unit and driver transformer for the new 430 MHz transmitter crowbar driver have arrived. We also have a spare for the large pulse transformer, which seems to be in as-new condition, and will be used in the new driver. The only part still to purchase is a modular 15kV, 5ma power supply. The new driver will be considerable smaller and much simpler than the old unit.

To: Edgar Castro

From: Jon Hagen

Date: May 16 2003

Subject: Week of May 12, 2003

Finished reviewing an NSF proposal but it was at least an educational exercise, relevant to the Alfa backend design project. Continued working on the Alfa problem.

Designed the 'finishing touches' for the new monoplexer (430 MHz receiver protector) - the biasing circuitry layout, including screw-in feedthrough decoupling capacitors, ferrite beads, and space for current limiting resistors. Completion of the monoplexer will require one or two days of shop work plus another day or two for adjustments - mostly to optimize the length of the section of line between the two diode stations.

New panels were built to hold the 16 new meters that monitor the 430 klystron solenoid currents and parts were ordered for the associated circuitry to emulate the under-current trip function of the old meters.

To: Edgar Castro

From: Jon Hagen

Date: May 23 2003

Subject: Week of May 19, 2003

Continuing on work to define the Alfa back-end processor(s). Am becoming familiar with the details of the resident pulsar machines.

Fixed a sudden failure in the new timing generator on the 430 MHz transmitter - during construction, an electrolytic capacitor had been installed with reversed polarity. It finally failed,

lowering the monoplexer command voltage below threshold. Diagnosis and repair took less than an hour. Victor Negron has replaced the panel of the Low-level Amplifier with a new panel, eliminating unused and obsolete controls. The only control remaining on the new panel is the drive attenuator. All the obsolete control circuitry was also removed from unit. The only console unit left to refurbish is the Low-Level Modulator, whose replacement panel will have a single switch, rather than a half dozen.

The body current detector for the 430 MHz klystrons is actually a 'ground fault' detector, in that it responds to current reaching ground from any part of the beam supply B- bus, whether it be inside one of the klystrons or outside in the power supply circuitry. Since we also measure the

individual klystron collector currents, we might think about installing some circuitry that would tell us whether a body current induced crowbar event was caused by a. an arc in Klystron A, b. an arc in Klystron b, or c. an arc from the power supply bus to ground.

To: Edgar Castro

From: Jon Hagen

Date: June 2, 2003

Subject: Week of May 26, 2003

Again spent most of the week mulling over the Alfa back-end requirements and searching for commercial DSP cores. Now feel ready to collaborate with Bill Sisk and Desh on hardware designs.

I was called in by Phil Perillat around 8pm on Friday night. The Vertex pointing system was dead in the water. Phil already guessed correctly that the problem was in the emergency stop chain. As before, we were hindered by the lack of documentation on the additional switches added here during installation of the system. Fortunately Luis Murray remembered two micro-switches added the fiber optic rotary joint machine to shut down the telescope in the event of a broken drive cable. The cable had not broken, but, with time, had slackened enough to trip one of these switches. We really should up-date the Vertex documentation to include our own additions, even if this means tracing out all the wiring. We should also improve our added emergency stop switches to the standard of the Vertex-supplied switches so that, if opened, the Vertex system will show the message "Emergency Stop."

To: Edgar Castro

From: Jon Hagen

Date: June 16, 2003

Subject: Weeks of June 2 and June 9, 2003

My conclusions on the architechture of the ALFA back-end are as follows:

1. The signals from the seven feeds are independent throughout the data-taking process and, except for map making, throughout subsequent data analysis. It therefore seems obvious to use seven separate processors, each with its own final data storage.

2. Each of the seven systems would have its own pair of A-to-Ds to sample the two polarizations. These digitizers could be in their own chassis, remote from the processor, with serial fiber optic connections to ensure that processor-generated noise is not fed back to the digitizers.

3. The main processing would be done on a board containing between 1 and 6 Altera or Xilinx FPGA chips. These chips would be loaded at run time with 'cores' and glue code appropriate for the observation: polyphase dft filtering or 'pipelined frequency transform' ( PFT) filtering.

4. The seven FPGA boards would be contained within seven Linux PCs (or within 14 PCs, if output data rates cannot be handled with 7 PCs).

5.Piggybacking would require either:

a. sufficient room in the FPGAs for simultaneous processes or

b. multiple FPGA boards in each PC or

d. WAAPs.

The Vertex pointing system again came to an emergency stop because of improper tension in the fiber optic drum drive cable. Mainenance had adjusted it after the previous incident, but not sufficiently. They have now realigned it and we expect to hold. Luis Murray has begun to trace the emergency stop wiring in order to update the Vertex schematics.

I completeted the bias injection design for the new monoplexer. Wilfredo Rosado is machining the brass diode station assemblies to accomodate the necessary resistors and feedthrough capacitors.

Mike Davis has requested a simple modification to the downstaits IF system to accomodate the Seti backend. It involves adding a pair of filters, which they will donate.

To: Edgar Castro

From: Jon Hagen

Date: June 20, 2003

Subject: Week of June 16, 2003

Worked on the plans for the redistribution of Electronics Dept. space that would accompany the planned Building 1.5. Produced a preliminary drawing that includes seven engineering offices plus increased laboratory space.

Chris Salter reported a 15 dB gain asymmetry in the two channels of the VLBI system. The problem was traced to a bad amplifier in one of the two IF Distributor modules. The amplifier was replaced.

The new monoplexer is almost completely assembled. I hope we can begin electrical tests and tuning next week.

Spent a day consolidating the pointing system documentation, checking out the LCU hot spare, and studying the data flow and timing relations between the LCU and PLC - the least documented and most impenetrable part of the Vertex system.

To: Edgar Castro

From: Jon Hagen

Date: July 3, 2003

Subject: Weeks of June 23 and June 30, 2003

Assembly of the new monoplexer was completed, and preliminary tests look good; the insertion loss is .08 dB (better than the old unit) and isolation is 66 dB (a couple of dB worse than the old units). The original designer was probably shooting for something like 90 dB of isolation. This is possible, given the low (0.1 ohm) on-resistance of the PIN diodes, but in the device, the series inductance of the diodes was not tuned out. I calculated that only 0.8 nH per diode would explain the observed 66dB. Made drawings of the final modifications to the original design and faxed them to Ithaca to be incorporated in the unit now under construction.

Revised a memo on polarization to include details of polarization measurement procedures using both correlation spectrometers and FFT spectrometers.

Dug out the original drawings for the cable wrap machine to find the dimensions of the casters used on the idler trolley. The wheels on these casters are worn and need replacement. Kurt Kabelac in Ithaca then found the original purchase orders and ordered a new set of casters.

The exhibition klystron is now mounted to a temporary dolly, ready for pressure washing. The klystrons stored in the transmitter room have been moved to the warehouse and the transmitter room is finally getting a complete clean up, which will include new floor tiles.

To: Edgar Castro

From: Jon Hagen

Date: July 18, 2003

Subject: Weeks of July 7 and July 14, 2003

The monoplexer drivers have been considerably modified and need rebuilding to physically tidy them up. However, there are still some improvements to be made, both in the logic circuitry and in the high voltage circuitry. I have been working with the SPICE simulator, modeling these changes. This modeling program will also be used in developing the new crowbar driver circuit.

I did a paper design for a 475 MHz notch filter to address the receiver intermodulation problem caused by two strong UHF television channels. Ganesh has already ordered a bandpass filter for this purpose, so this design might not be used. However, I think the design technique may be useful; the notches are made only deep enough to suppress the offending 3rd-order products, but still shallow enough to keep the in-band filter loss below .08 dB.

The display klystron is now cleaned up, ready for exhibition. I produced a poster to explain its innards to visitors - or, at least, to visiting engineers. Cutting this tube open for display was something of a post mortem examination, as we found that the beam tube is severely melted at its gap in the third cavity, indicating that improper tuning had occurred at Thule. (This tube was inoperable when it arrived at Arecibo1986, but not because of rough handling during shipment).

The new (and first) oil cooling system is being installed on the 430 transmitter. Defective magnet current meters have removed from the console and replaced with a newly built metering panel.

Work continues on replacing the floor in the transmitter room.

Mike Sulzer informs me that SRI is willing to give us two solid state amplifier modules, prototypes for their proposed phased array incoherent scatter radar. These modules could provide a wide-band replacement for our current driver amplifier, which is currently the bottle neck in the 430 transmitter.

To: Edgar Castro

From: Jon Hagen

Date: Aug. 8, 2003

Subject: Weeks of July 21 and July 28, 2003 (Week of Aug. 4 was vacation)

I have the new monoplexer driver circuitry 90% designed. The logic portions will be on a separate board from the high current switching section.

Assisted in troubleshooting the S-band transmitter when the emergency stop logic prevented bringing the system up. Victor Iguina and I became considerable more familiar with this system during this repair.

Installed newer version of the EASYCAD drafting program. Used this version to produce PDF versions of the latest updated set of IF/LO block diagrams for the web site. (Karen O'Neil had previously done the conversions to PDF when these drawings were updated).

Victor Iguina's two student workers gave the display a final cleaning and touch-up painting and applied a clear coat to the shiny exposed copper surfaces. They have also readied the floor of the transmitter room for new tiles, to be put down by the maintenance department.

To: Edgar Castro

From: Jon Hagen

Date: Aug. 25, 2003

Subject: Weeks of Aug. 10 and Aug 17, 2003

Victor Iguina has the oil cooler heat exchanger mounted on the pad in aluminum housing for weather protection. Once the plumbing connections are made to the oil lines, the unit will be operational. The low-level modulator in the 430MHz transmitter console was fitted with a new front panel, retaining a single control switch and eliminating six obsolete and confusing switches. Several unused connectors were also weeded from the rear panel. This completes the refurbishing of the console control units.

Worked with Jose' Maldonado on the lower grease cup design for the reflector panel adjustors.

We think these units can be nothing more than a short length of hose (neoprene or other uv and grease resistant material) pre-loaded with grease and clamped to the 5/8" jack screw with a nylon cable tie wrap.

I am awaiting delivery of a new desktop pc ($1185) which will have enough memory (1MB) to run HFSS with ease. This finite element electromagnetic design program had previously been run on a dedicated (now obsolete) computer set up on a no-longer-available desk. With HFSS again available, I plan to revisit the half-height turnstile design to improve the isolation between the transmitter and receiver ports. Apparently this isolation was reduced when a corona ball was installed to prevent arcing. A related job for HFSS is investigation of objectionable beam squint in the 430MHz Gregorian feed.

I have been detailing the design for the new monoplexer drivers - assigning part numbers and working on the board layout for the critical current paths. The new drivers are 1/3 of the effort to provide bullet- proof receiver protection. The other thirds are the turnstile isolation question and the installation of instrumentation to monitor the power incident on the monoplexers and the monoplexer isolation.

We have built a pair of hand-held 9GHz circular polarization test antennas which use reflective quarter- wave plates (Quasioptical Systems, Paul F. Goldsmith, p.198). One of these antennas is Left-Hand Circular while the other can be switched to either LHC or RHC. The purpose of these antennas is to provide an absolute verification, whenever necessary, of the polarization of the X-band receiver channels. This is to eliminate the embarrassment of submitting VLBI tapes with the warning that the polarizations might be reversed. (Very small helical antennas had produced questionable results).

To: Edgar Castro

From: Jon Hagen

Date: Aug. 29, 2003

Subject: Week of Aug. 25, 2003

I have been trying to find information on the high power TWTs used in the DARPA UHF transmitter in the Altair radar, which transmits 5MW at 422 MHz with 15MHz bandwidth (vs. our 1 MHz bandwidth). The tubes seem to be made by L-3 Communications (once Litton) at a division in Williamsport, Pa. Stephen Hunt of Lincoln Lab, who recently visited Arecibo, seems to have done meteor observations with Altair using 150us pulses with a 333Hz PRF (a duty factor of 5%). I am contacting L-3 to see if the tubes are available for non-defense-related uses, just to know what kind of 'ultimate' 430MHz transmitter might be possible for Arecibo.

I found several vendors of handheld radiation detectors. These units, costing as little as $30, provide digital readout of field strength. Some models are made specifically for measuring leaking from microwave ovens ad 2450 MHz. These should be ideal for our 2380MHz radiation safey surveys. Other inexpensive units provide coverage from UHF up, allowing measurements at 430MHz. We should purchase and evaluate several of these units to complement our expensive (and unreliable) NARDA instrument.

The 430MHz transmitter, when tested for an upcoming run, showed a periodic variation in power output, most noticible with an IPP of 16ms (PRF = 62.5Hz). This was suggestive of power supply ripple and two blown high-voltage rectifiers were found and replaced. It would be quite simple to install a current transformer at the low voltage side of the power supply to provide a console-mounted jack for monitoring the total rectifier current. A blown rectifier would be immediately obvious. I also spent several hours this week updating the 430 Mhz transmitter manual.

Our tiedown systems continue to suffer lightning damage. To improve our grounding system, we need to know the path(s) taken by the current. Does it actually get to ground via the intended ground wire, or does it find another path, (.g. through the anchor block) A German company, OBO Bettermann, makes a system to monitor lightning induced currents in cables. The sensor is simply the magnetic strip on an ordinary credit card. Cards are fixed to cables with the magnetic strips extending out radially. After a lightning strike, the cards are read with a reader that looks like a shoebox with an ATM card slot. This reader indicates the peak value of the current. Presumably, after reading, the card can be erased to make it ready for another event. We should look into the cost of this system, which obviously would be useful for our tower ground systems.

To: Edgar Castro

From: Jon Hagen

Date: Sept. 4, 2003

Subject: Week of Sept 2, 2003

Revisited the problem of isolating the front panel Amplifier outputs in the IF/LO system. This system has eight 8-way amplifiers, allowing several back-ends to be left connected, whether or not more than one is in use at any time. In each unit, one of the eight outputs feeds a front panel monitor port, which is normally left unterminated or, worse, left connected to a random filter or cable. Due to insufficient reverse isolation in the amplifier feeding this port, the improper terminations cause base line ripples in the signals exiting the other ports. Replacing the amplifier with a higher gain amplifier and a pad reduced the ripples by 12 dB, as predicted. This improvement was deemed insufficient, however, so I suggested using a combination of two amplifier and three pads, which should reduce the ripples by 25db. Bill Sisk installed this combination, which worked as expected. This modification should now be made to the remaining seven amplifiers.

Made two modifications to the 430MHz transmitter reflected power alarm/shut-off unit: The threshold range was increased by a factor of two and a small bias was added so that the unit can be test tripped by turning the threshold knob down to 10% of full scale.

Charles Malcolm of L-3 Communications answered my query regarding the very wide-band UHF TWTs used at Altair:

"Currently there is no commercial version of the ALTAIR tube available but I would not anticipate that too much time or money would be expended to develop one. The tube would have similar performance characteristics and would possibly just entail external (to the vacuum envelope) changes to the package. This is something we would certainly be interested in discussing. For example the following will give you some idea of what the TWT will do in your band of interest:

cathode voltage = 40 [kV]

cathode current = 14 [amps - peak]

max pulse width = 1400 [microsec]

max duty factor = 6.0 %

basic electronic efficiency = 48 % (dual stage collector - standard)

peak power output = 200 [kW]

liquid cooled (water / glycol)

I believe ALTAIR is currently utilizing 24 tubes simultaneously with plans to go to 32. The transmitters are some of the old Raytheon CRS-70 units "borrowed" from a Naval vessel, the Vandenburg I think. Anyway, I hope this information is of value and please don't hesitate to contact us if we can be of any further assistance.

regards, chuck malcolm"

I will ask what he meant by "not too much money". Another obvious wide-band transmitter would be made of a great many solid-state modules, such as those being developed by SRI for the Polar Cap Radar.

To: Edgar Castro

From: Jon Hagen

Date: Sept. 12, 2003

Subject: Week of Sept 8, 2003

I looked into the 'weight and overlap' spectrometry algorithm used at Berkeley and suggested by Carl Heiles for use in the G-Alfa spectrometer. Jeff Hagen has been implementing this method in a prototype G-Alfa 'software spectrometer'. A simple modification speeds up this method by allowing the use of a single FFT rather than a bank of FFTs to produce the overlapped spectra. A further simplification, however, produces the Weight-Overlap-Add (WOLA) version of the 'polyphase filter bank" which, besides doing the necessary overlapping to prevent loss of sensitivity, also permits the synthesis is of any desired bandpass shape. The Berkeley method used the usual ad-hoc weights (tapering) to strike a compromise between line width broadening and. sidelobe suppression. Conclusion: the Berkeley method seems to have been a step in the evolution of the poly-phase filter.

To: Edgar Castro

From: Jon Hagen

Date: Sept. 19, 2003

Subject: Week of Sept 15, 2003

Edgar Castro, Rey Velez, and I measured the field strength of the S-band transmitter at the Visitor Center observation point. This has, of course, been done before, but was re-checked in view of a recent reading made at the base of Tower 4, which is at the same elevation. The observed power density at the Visitor Center seemed to be less than about 0.1 mw/cm^2 for any position of the dome except when the azimuth is about 177 deg and the dome zenith angle is above 19.2 degrees. In this position, the dome is as far as possible from the observation point, and we suppose the increased power is due to specular reflection from the ground screen. For this special position, observed field strengths reached 2mw/cm^2, which is double the FCC limit for General Population/Uncontrolled Exposure. However, the FCC limit is specified over a 30 minute averaging time, so a 2mw/cm^2 exposure for 15 minutes, followed by zero exposure for the next 15 minutes would be allowed. In practice, this is not a point at which we hover, waiting for a source to come into view. During a scan, time spent at this position is generally brief.

The guard house at the base of Tower 4 is the other inhabited spot at this high elevation, and the power there was observed to range between 1 and 2mW/cm^2. However, the FCC limit for Occupational/Controlled Exposure is 5 mW/cm^2 (and this is half the of the pre-1991 maximum of 10mW/cm^2).

The renovation of the transmitter room is proceeding quickly. The floor tiles have been replaced, and unsightly junk is being removed.

I made two complete copies of the 430MHz Transmitter Manual and of the complete set schematic diagrams. One set will be used by the transmitter technicians, while the other set will be for Joe Greene, the new transmitter engineer who is scheduled to start work next Monday. I plan to spend a week or two going over this documentation with him to get him started.

The company L-3 Communications furnished more information on high power 430MHz traveling wave tubes ( TWTs). The tubes come with internal focusing coils; no external solenoids are required. They also have conventional control grids to turn the beam on and off, so no high power modulator is needed. The company promises to furnish more information - pictures, specs, and prices.

I received a new Dell desktop computer and have installed the programs I routinely use. I also have installed our Ansoft HFSS finite element electromagnetic simulation program, which would not run on my older machine. (We used it with before with dedicated computer. That computer, and the desk it occupied had been taken over for other uses). With this program back in operation, we can fine-tune the dome turnstile junction to improve its isolation and provide better receiver protection.

To: Edgar Castro

From: Jon Hagen

Date: Sept. 19, 2003

Subject: Weeks of Sept 22 and Sept 29, 2003

I spent considerable time during this period with Wm. J. (Joe) Greene, our new transmitter engineer, explaining the operation of the 430 MHz transmitter. Joe picks up this material very quickly; his prior experience with the big Navy low-frequency transmitter in Aguada is totally applicable to our high- power transmitters. After one week, he was troubleshooting the collector current metering circuitry: the collector current meters for the two klystrons had abnormally different readings. He found the problem - one of the meters was defective - fixed the meter, calibrated the metering circuit and wrote up his calibration procedure in ISO9000 format. This written procedure, together with many more I anticipate him making, will be added to the still-growing transmitter manual. He then looked for the cause of an abnormally low reading for the IPA forward power meter, finding a broken directional coupler. The coupler was then repaired. Joe is also quite expert in CAD drawing, and is already set up to modify and edit all the schematic diagrams for the 430 Transmitter.

Wanda made copies of the S-band operation and maintenance manuals for Joe Greene and me. Joe and Wm. Iguina observed Victor Negron, operating the S-band transmitter during a series of runs.

I think Joe will have no trouble coming up to speed on both the S-band and the 430MHz transmitters.

Even though we have a written and posted safety rule that nobody go to the platform during any 430 transmitter operations, two receiver technicians were spotted working in the Gregorian dome during a dual beam operation that lasted several days. They knew the policy, but mistakenly thought that only the carriage house antenna was being used. The transmitter was turned off while they made their way down, causing an unscheduled interruption of the experiment. The telescope operator had properly disabled the cable car, but the technicians had gone up via the catwalk. We must continue to insist on compliance with this safety policy and make sure all employees know that cannot be sent to the platform during transmitter operations nor can they go up on their own accord. We should also try to have a daily break scheduled into all multi-day runs, to allow for normal daily maintenance of platform equipment. Finally, we should install a sign and a flashing light at the bottom end of the catwalk and do the same in the cable car launch house.

To: Edgar Castro

From: Jon Hagen

Date: Oct. 24, 2003

Subject: Weeks of Oct. 6 and Oct 20, 2003 (On vacation week of Oct 13)

Transmitter activities:

1. Installed reduced gear ratio autotransformer for the second magnet in the S Band transmitter.

2. New control cable run begun by the Platform Crew for the S Band transmitter.

3. Installed a directional coupler at the beginning of the 430 MHz waveguide run (after the EH tuner). Ran RG-9 coaxial cables from the coupler to the console of the 430MHz transmitter to monitor the SWR in the waveguide. The first measurement yielded a return loss of 14 dB (VSWR of 1.5), which is satisfactory.

4. Replaced out-of tolerance high voltage metering resistors installed in the 430 MHz transmitter. Cleaned and checked the metering tower.

5. Tested S Band transmitter, one tube at a time, to identify whiche tubes is causing excessive body current during special experiments.The test was inconclusive due to a problem with the klystron magnet controls.

6. Several magnet problems found, including incorrect cabling in the new autotransformer for Klystron 1 and a bad solid state relay.

7. Installed fiber optic cable to the ionosonde.

I received a quotation for strain insulators that can be installed in the tie-down cables to provide lightning protection for the tie-down electronics. The A-S8027S, made by Austin Insulators, Inc. is rated for a safe working load of 60,000 lbs (ultimate tensile strength is 180,000 lbs). It will stand off 50kV rms (70.7kV peak), weighs 130 lbs, and costs $3440.00.

Located a type of PVC tubing which might be suitable for the reflector lower grease cups, if the threaded design proves too expensive.

Wrote a memo as a rough cut for an RFP, should we decide to replace the control portion of the Vertex pointing system.

To: Edgar Castro

From: Jon Hagen

Date: Oct. 24, 2003

Subject: Weeks of Oct. 27 and Nov. 3, 2003

Transmitter activities:

Klystron 1 in the S-band transmitter failed; its vacuum deteriorated by several orders of magnitude, though not enough to burn out the filament. The failure was not sudden, i.e. it did not coincide with a crowbar event or other automatic shutdown. The only abnormal operating condition observed was that the reflected power into this tube had become noticeably higher than that into Klystron 2. Since the power from the two tubes is combined very near the tubes, this asymmetry must have been caused by a defect in the combiner or in the elbow or waveguide switch preceding the combiner. High reflected power during an arc may have damaged the klystron's waveguide window, though damage is not visibly evident. Some small arc pits can be seen in the combiner, yet it seems unlikely that these minute pits are causing the observed reflection. The transmitter was reconfigured to use only Klystron 2. Before two- tube operation is restored, we will measure the return loss on both sides of the elbow/waveguide switch/combiner network. The arc detector test lamp for Klystron 1 failed;

Joe Greene got a quote for new high voltage metering resistor for the 430 transmitter; the old resistor is large, in the way, and sometimes intermittent.

A solid-state replacement was designed for the cable driver amplifier that feeds a sample of the 430 transmitter floating deck voltage to the operating console. The old vacuum tube amplifier was large and inconveniently located and undesirably 'robbed' its high voltage from a distant power supply on the crow-bar driver chassis. William Iguina constructed the new unit and we will install it this week.

We are replacing aged electrolytic capacitors in the IPA, whose output signal has acquired some 60Hz 'hum' modulation. Unrelated to his problem, Mike Sulzer, in trying out a new 8-pulse scheme, found some distortion in the low-level consol-mounted RF driver circuitry. We plan to go through the entire RF chain, adjusting for maximum bandwidth and symmetry about 430 MHz.

Dan Wertheimer and Aaron Parsons, visiting from UC Berkeley, described techniques they have used in building their FPGA spectrum analyzers; we plan to follow the same development steps for the ALFA processors.

To: Edgar Castro

From: Jon Hagen

Date: Sept. 19, 2003

Subject: Week of Sept 15, 2003

Edgar Castro, Rey Velez, and I measured the field strength of the S-band transmitter at the Visitor Center observation point. This has, of course, been done before, but was re-checked in view of a recent reading made at the base of Tower 4, which is at the same elevation. The observed power density at the Visitor Center seemed to be less than about 0.1 mw/cm^2 for any position of the dome except when the azimuth is about 177 deg and the dome zenith angle is above 19.2 degrees. In this position, the dome is as far as possible from the observation point, and we suppose the increased power is due to specular reflection from the ground screen. For this special position, observed field strengths reached 2mw/cm^2, which is double the FCC limit for General Population/Uncontrolled Exposure. However, the FCC limit is specified over a 30 minute averaging time, so a 2mw/cm^2 exposure for 15 minutes, followed by zero exposure for the next 15 minutes would be allowed. In practice, this is not a point at which we hover, waiting for a source to come into view. During a scan, time spent at this position is generally brief.

The guard house at the base of Tower 4 is the other inhabited spot at this high elevation, and the power there was observed to range between 1 and 2mW/cm^2. However, the FCC limit for Occupational/Controlled Exposure is 5 mW/cm^2 (and this is half the of the pre-1991 maximum of 10mW/cm^2).

The renovation of the transmitter room is proceeding quickly. The floor tiles have been replaced, and unsightly junk is being removed.

I made two complete copies of the 430MHz Transmitter Manual and of the complete set schematic diagrams. One set will be used by the transmitter technicians, while the other set will be for Joe Greene, the new transmitter engineer who is scheduled to start work next Monday. I plan to spend a week or two going over this documentation with him to get him started.

The company L-3 Communications furnished more information on high power 430MHz traveling wave tubes ( TWTs). The tubes come with internal focusing coils; no external solenoids are required. They also have conventional control grids to turn the beam on and off, so no high power modulator is needed. The company promises to furnish more information - pictures, specs, and prices.

I received a new Dell desktop computer and have installed the programs I routinely use. I also have installed our Ansoft HFSS finite element electromagnetic simulation program, which would not run on my older machine. (We used it with before with dedicated computer. That computer, and the desk it occupied had been taken over for other uses). With this program back in operation, we can fine-tune the dome turnstile junction to improve its isolation and provide better receiver protection.

To: Edgar Castro

From: Jon Hagen

Date: Sept. 19, 2003

Subject: Weeks of Sept 22 and Sept 29, 2003

I spent considerable time during this period with Wm. J. (Joe) Greene, our new transmitter engineer, explaining the operation of the 430 MHz transmitter. Joe picks up this material very quickly; his prior experience with the big Navy low-frequency transmitter in Aguada is totally applicable to our high- power transmitters. After one week, he was troubleshooting the collector current metering circuitry: the collector current meters for the two klystrons had abnormally different readings. He found the problem - one of the meters was defective - fixed the meter, calibrated the metering circuit and wrote up his calibration procedure in ISO9000 format. This written procedure, together with many more I anticipate him making, will be added to the still-growing transmitter manual. He then looked for the cause of an abnormally low reading for the IPA forward power meter, finding a broken directional coupler. The coupler was then repaired. Joe is also quite expert in CAD drawing, and is already set up to modify and edit all the schematic diagrams for the 430 Transmitter.

Wanda made copies of the S-band operation and maintenance manuals for Joe Greene and me. Joe and Wm. Iguina observed Victor Negron, operating the S-band transmitter during a series of runs.

I think Joe will have no trouble coming up to speed on both the S-band and the 430MHz transmitters.

Even though we have a written and posted safety rule that nobody go to the platform during any 430 transmitter operations, two receiver technicians were spotted working in the Gregorian dome during a dual beam operation that lasted several days. They knew the policy, but mistakenly thought that only the carriage house antenna was being used. The transmitter was turned off while they made their way down, causing an unscheduled interruption of the experiment. The telescope operator had properly disabled the cable car, but the technicians had gone up via the catwalk. We must continue to insist on compliance with this safety policy and make sure all employees know that cannot be sent to the platform during transmitter operations nor can they go up on their own accord. We should also try to have a daily break scheduled into all multi-day runs, to allow for normal daily maintenance of platform equipment. Finally, we should install a sign and a flashing light at the bottom end of the catwalk and do the same in the cable car launch house.

To: Edgar Castro

From: Jon Hagen

Date: Oct. 24, 2003

Subject: Weeks of Oct. 6 and Oct 20, 2003 (On vacation week of Oct 13)

Transmitter activities:

1. Installed reduced gear ratio autotransformer for the second magnet in the S Band transmitter.

2. New control cable run begun by the Platform Crew for the S Band transmitter.

3. Installed a directional coupler at the beginning of the 430 MHz waveguide run (after the EH tuner). Ran RG-9 coaxial cables from the coupler to the console of the 430MHz transmitter to monitor the SWR in the waveguide. The first measurement yielded a return loss of 14 dB (VSWR of 1.5), which is satisfactory.

4. Replaced out-of tolerance high voltage metering resistors installed in the 430 MHz transmitter. Cleaned and checked the metering tower.

5. Tested S Band transmitter, one tube at a time, to identify whiche tubes is causing excessive body current during special experiments.The test was inconclusive due to a problem with the klystron magnet controls.

6. Several magnet problems found, including incorrect cabling in the new autotransformer for Klystron 1 and a bad solid state relay.

7. Installed fiber optic cable to the ionosonde.

I received a quotation for strain insulators that can be installed in the tie-down cables to provide lightning protection for the tie-down electronics. The A-S8027S, made by Austin Insulators, Inc. is rated for a safe working load of 60,000 lbs (ultimate tensile strength is 180,000 lbs). It will stand off 50kV rms (70.7kV peak), weighs 130 lbs, and costs $3440.00.

Located a type of PVC tubing which might be suitable for the reflector lower grease cups, if the threaded design proves too expensive.

Wrote a memo as a rough cut for an RFP, should we decide to replace the control portion of the Vertex pointing system.

To: Edgar Castro

From: Jon Hagen

Date: Nov. 7, 2003

Subject: Weeks of Oct. 27 and Nov. 3, 2003

Transmitter activities:

Klystron 1 in the S-band transmitter failed; its vacuum deteriorated by several orders of magnitude, though not enough to burn out the filament. The failure was not sudden, i.e. it did not coincide with a crowbar event or other automatic shutdown. The only abnormal operating condition observed was that the reflected power into this tube had become noticeably higher than that into Klystron 2. Since the power from the two tubes is combined very near the tubes, this asymmetry must have been caused by a defect in the combiner or in the elbow or waveguide switch preceding the combiner. High reflected power during an arc may have damaged the klystron's waveguide window, though damage is not visibly evident. Some small arc pits can be seen in the combiner, yet it seems unlikely that these minute pits are causing the observed reflection. The transmitter was reconfigured to use only Klystron 2. Before two- tube operation is restored, we will measure the return loss on both sides of the elbow/waveguide switch/combiner network. The arc detector test lamp for Klystron 1 failed;

Joe Greene got a quote for new high voltage metering resistor for the 430 transmitter; the old resistor is large, in the way, and sometimes intermittent.

A solid-state replacement was designed for the cable driver amplifier that feeds a sample of the 430 transmitter floating deck voltage to the operating console. The old vacuum tube amplifier was large and inconveniently located and undesirably 'robbed' its high voltage from a distant power supply on the crow-bar driver chassis. William Iguina constructed the new unit and we will install it this week.

We are replacing aged electrolytic capacitors in the IPA, whose output signal has acquired some 60Hz 'hum' modulation. Unrelated to his problem, Mike Sulzer, in trying out a new 8-pulse scheme, found some distortion in the low-level consol-mounted RF driver circuitry. We plan to go through the entire RF chain, adjusting for maximum bandwidth and symmetry about 430 MHz.

Dan Wertheimer and Aaron Parsons, visiting from UC Berkeley, described techniques they have used in building their FPGA spectrum analyzers; we plan to follow the same development steps for the ALFA processors.

To: Edgar Castro

From: Jon Hagen

Date: Nov. 14, 2003

Subject: Week of Nov. 10, 2003

Transmitter activities:

The two old warehoused S-band klystrons were inspected. Tube L9-1R1 had good vacuum and responded well to the application of filament power (the vacuum remained good). However, the other Tube, G0-1R1 had a high vac-ion pump current (100mA) indicating lost vacuum. This was confirmed by interchanging the vac-ion pump control units.

We plan to install L9-1R1 on Dec. 3. The failed new tube will be taken down on Dec 1. The cooling water will be replaced on Dec. 4, leaving Dec. 5 for one day of testing before scheduled S-band runs.

A stock of light bulbs has been ordered for the S-band transmitters arc detector test circuits. Some fiberglass "L" stock has also been ordered to replace two sections that are damaged from high voltage 'treeing'. The replacement control cable was installed between the rotary joint and the dome. The only remaining section needing replacement is between the power supply building and the control building.

The newly built solid-state cable driver amplifier was installed to monitor the 430 MHz transmitter's floating deck voltage. A long 430 MHz run got off to a rocky start when Mike Sulzer found his 7-pulse scheme was producing poor data. (He had noted a problem earlier with a new 8-pulse scheme). This was corrected by re-tuning the external cavities for IPA klystron. These cavities may have been disturbed when the entire IPA cabined was temporarily moved to install new floor tiles, several weeks ago.

To: Edgar Castro

From: Jon Hagen

Date: Nov. 21 2003

Subject: Week of Nov. 17, 2003

Transmitter activities:

The S-band transmitter had a telemetry failure; erroneous vac-ion and water pressure readings were being sent downstairs, preventing system operation. Joe Greene found that the mother board in the upstairs instrumentation - a big (maybe 18" x 12" ) board, was encrusted with black sandblasting grit and had corroded traces. He and Victor Negron installed a new board (we had a spare) and cleaned the daughter boards. The telemetry then worked. An unrelated fault then occurred; the system would shut down at the moment the high voltage was turned on. The fault was traced to the top ignitron in the crowbar unit. This tube was replaced and the system operated normally.

Pointing system:

On Saturday, Nov. 15, it suddenly became impossible to run the azimuth drive in 'tracking' mode. The failure was peculiar in that, while the azimuth, wouldn't track, it would obey 'preset' commands. The other axes were working fine. That suggested that the encoders and motors were ok and that the PLC and LCU computers were, at least, mostly ok. After considerable preparation we had a diagnostic system plugged into the PLC by Tuesday morning. The program seemed to operate normally (correct command data flowing from the LCU to the PLC); operation had spontaneously returned to normal. All of this correlates with terrific rains and then a period of drying out, but the symptoms pointed to the digital control system. Our ability to troubleshoot this Vertex-built digital system continues to be unsatisfactory. This was discussed in a meeting on Friday where there was unanimous agreement that the system should be replaced with a more manageable design, but that, for now, with other pressing commitments, we will try to buy time, making sure all of our hot spares have actually been tested on the platform.

To: Edgar Castro

From: Jon Hagen

Date: Dec. 5, 2003

Subject: Weeks of Nov. 23 (3 days) and Dec. 1, 2003

Pointing System: Phil Perella and Luis Murray got LCU No. 5, our first Pentium LCU, working as a spare. This unit ran correctly with our "Lab Test" version of the program, but did not work when it was substituted for questionable LCU No. 4, the last of the 486 LCUs) on the platform while trouble- shooting the azimuth problem two weeks ago. No. 5 was left running on the platform. No.6, a second spare, was configured to match No. 5 and was tested on the platform.

Transmitter activities:

The failed S-band klystron was replaced this week with the one good klystron left from the 500kW transmitter. This tube is not quite identical to the newer "A" model. Enough alignment adjustment is provided in the transmitter to make it fit, but, if its phase characteristics are significantly different, the transmitter may run at somewhat reduced power when it is phase modulated. During installation we discovered that this klystron's waveguide switch (that can select a dummy load) showed evidence of arcing at the joint between rotor and stator. This would explain the observed increase in reflected power. A hairline crack can be seen in the BeO window of the failed tube. This may have been caused by reflected power in an event where the reflected power monitoring circuit failed to shut of the RF drive.

430MHz System

I have HFSS (finite element electromagnetics) running on my desktop computer, and have re-run the model of the half-height turnstile - the OMT used in the dome. I modified the model to include the 1.5" diameter ball which we added to the post to suppress arcing. As expected, this ball hardly effects the performance of the turnstile. In particular, the transmitter-to-receiver isolation remains at about 29 dB.

Nevertheless, Ganesh has made measurements that found poor isolation (15 to 20 dB) in both the dome and carriage house systems. The carriage house turnstile has not been inspected or retuned in perhaps 20 years. This should be done, but first we should do a careful inspection of the line feed, since any degradation of its match will degrade the receiver isolation. The HFSS model of the carriage house turnstile provides a reliable check on the setting of its side short positions. Once both systems are restored to original performance, I think we can further improve the isolation by introducing a small reflecting puck in the circular output waveguide, whose size and position will provide just the right cancellation of the leakage into the receiver. These pucks would not only provide a method of fine-tuning the turnstile junction (especially the fixed-tuned compact turnstile in the dome, but would also allow us to tune out leakage caused by reflections from the line feed and horn.

We are awaiting the arrival a two solid-state amplifier units from SRI which will be configured for use as a wide-band driver for the 430 klystrons.

To: Edgar Castro

From: Jon Hagen

Date: Dec. 12, 2003

Subject: Week Dec. 8, 2003

Transmitter activities:

The S-band transmitter suffered a series of faults, causing several runs to be canceled. These apparently unrelated failures included a burned Variac in one of the magnet power supplies, a burned coil in a control relay (1A11XK4), and a failure in the high voltage turn-on circuitry - the big problem. When commanded to turn on, the high voltage would turn off again almost immediately. The control system

indicated "excessive klystron current" and "crowbar triggered", though the crowbar had not actually fired.. However, when the high voltage wire to the dome was disconnected, the fault persisted, suggesting that the problem was somewhere in the power supply building. Yet we found nothing wrong in this building. Finally the problem was located upstairs in an intermittent connection in the twisted pair connecting the current measuring shunt resistor to a differential sense amplifier. Apparently one wire in the pair was making intermittent contact in a connector. The differential amplifier therefore became a common mode amplifier, detecting the turn-on transient on the HV return cable (which had not been disconnected) from the floating HV power supply. It remains to bring up the power and set the proper differential phase in the drive to the two klystrons. Our learning curve has been steep during this troubleshooting and mean time to repair should decrease as our new engineer, Joe Greene, becomes completely familiar with the system.

430 Transmitter

We received two 500W solid-state amplifiers from SRI. These units have built in pulsers, triggered by a simple TTL signal. Their gain is 50 dB. We will first install a single amplifier. If 500W is insufficient to drive the 430 MHz klystrons, we combine the power of both amplifiers, but we expect that one amplifier will be sufficient, leaving the second as a spare. The bandwidth of these amplifiers is 20 MHz, compared to only 1MHz for our present driver (a small klystron).

To: Edgar Castro

From: Jon Hagen

Date: Jan. 22, 2004

Subject: Week of Dec. 15, 2003

Transmitter activities:

We have set the proper differential drive phase for the S-band klystrons. However the transmitter brought its high voltage down several times during the adjustment procedure, after falsely detecting a coolant flow problem. This failure is similar to the false body current indication of last week. The only opportunity to correct this problem before many January runs is during scheduled maintenance periods on the last three days of this month. There are also a number of other S-band issues that need attention, including troubleshooting of the house power circuits that allow testing without running the turbine.

430 Transmitter

Once again this transmitter got off to a bad start on a multi-day run. A broken cooling hose had been replaced. The replacement hose, apparently not quite the right size, worked its way off a nipple connection, spilling many gallons of water into the klystron vault. The spill was cleaned up and the transmitter turned on, under the assumption that little or no water had leaked down into the socket and modulator tank. On past occasions, there have been slight amounts of water in the tank, but that water settled to the bottom and caused no operational problem. When the high voltage was brought up, a strong arc occurred in the tank, next to the base of one of the klystrons. This arc, probably due to a water bubble in the oil, shocked the klystron, breaking an aluminum corona ring and short circuiting the filament.All 2000 gallons of oil were pumped out of the tank and filtered. Water, maybe a quart or more, was mopped from the bottom of the tank. The tank was cleaned with alcohol and allowed to dry. The klystron was replaced and the tank refilled with the filtered oil. Twenty-four hours later, the transmitter is being run at about 1MW output to age the replacement klystron, whose vacuum is slowly improving.

To: Edgar Castro

From: Jon Hagen

Date: Jan. 9, 2004

Subject: Weeks of Dec. 22, 2003 (1days), Dec, 29, 2003 ( 3 days) and Jan 5, 2004 (3 days)

Transmitter activities:

Vacuum continued improve in the recently-installed klystron in the 430 MHz transmitter during a multi- day run in which the power level was 1.9MW. Now that we have installed a directional coupler in the waveguide run to the platform, I plan to install a metering circuit in the console to provide a constant indication of the magnitude of the reflection coefficient. This will give us an immediate indication of any problem in the waveguide run, e.g. broken or cracked flex sections.

Dec. 29, 30, and 31 were devoted to getting the S-band transmitter operation for a series of New Year runs. The backup arc detectors were fixed and the directional couplers at the outputs of the klystrons were calibrated. Another mother board for the monitoring cabinet has been ordered from Continental, after we used our spare to replace the damaged original board. We have also requested that Continental furnish us with the transmitter manual and schematics in digital form so that we can properly update and maintain this documentation. A Variac was ordered to replace the magnet supply variac that burned out several weeks ago.

I wrote a long memo detailing the 430 MHz and S-band turnstile junction OMTs used at the observatory. The memo includes detailed drawings, tuning procedures, and swept-frequency S- parameter data calculated with HFSS.

To: Edgar Castro

From: Jon Hagen

Date: Jan. 16, 2004

Subject: Week of Jan 12, 2004

This week was spent on intense maintenance of the S-band transmitter. High reflected power at Klystron 1 occurred and was traced to that klystron's waveguide switch. The switch was removed and brought down to the lab. The transmitter was replumbed to operate with a single klystron. In the lab, the failed switch was disassembled. There was oil - some of burned - inside the switch. This oil had gradually seeped in from the unsheilded ball bearings, and was likely the cause of the failure. Burned patches on the faces of the rotor and stator were cleaned and polished. The switch was reassembled, tested, and reinstalled upstairs. The transmitter came up to full power in the 2-tube configuration, but both waveguide arc detectors for Klystron 2 became intermittant. A run was scratched, rather than running without reliable arc detection. Today, Friday, the arc detectors have again been adjusted and tested. Then the entire transmitter was brought up to full power and run for about 30 minutes with no problems noted. The transmitter was then turned off and the arc detectors were found to still pass their test.

It is clear that the arc detector arrangement is marginal at best. We should redesign these detectors, just as we should improve the servo controlled magnet and filament circuitry and the generator-to-house- power switch gear.