To: Edgar Castro

From: Jon Hagen

Date: Jan. 23, 2004

Subject: Week of Jan 19, 2004

430 MHz Transmitter: Assisted the receiver department in tuning the turnstile junction in the Carriage House. A vector network analyzer was used to tune one side short and the inner central post for

best match and least cross coupling. The coupling was reduced from -17dB to -40dB, which should allow us to go back to cryogenic receivers without burning them out. This improvement represents only about 1/4 displacement of the side short. These shorts are held only by friction and at least one must have shifted. At the same time, the match to CRR2, the receiver that shares the transmitter port, degraded to about -10dB return loss. We will repeat this procedure using our WR2100 waveguide cal kit, which will let us achieve an essentially perfect set up of the turnstile. Then we can investigate whether the Y-switch is degrading the match to CRR2.

The S-band transmitter again required repair work. A small relay had failed in the emergency off interlock chain and was replaced. This was done today, and the transmitter was tested successfully at full power.

To: Edgar Castro

From: Jon Hagen

Date: Jan. 30, 2004

Subject: Week of Jan 26, 2004 (1 day of vacation)

Worked on calibrating the directional couplers that measure forward and reflected power at the klystrons and antenna of the S-band transmitter. Drew individual detailed diagrams of these metering circuits with levels, scale factors etc from the couplers on down to the CRT screen of the operator's terminal. Designed work sheet forms to be used whenever these circuits are re-calibrated. Victor and Joe carried out the calibration procedures.

A test jig was built for the S-band transmitter's metering cards. It was immediately used on a failed card. A faulty IC comparator was identified and replaced. The card was then successfully tested in the transmitter.

Arranged to attend ALFA acceptance tests in Australia in March after both Ganesh and German Cortes were unable to obtain travel visas.

To: Edgar Castro

From: Jon Hagen

Date: Feb 10, 2004

Subject: Week of Feb 2, 2004

Continued work on calibrating the directional couplers that measure forward and reflected power at the klystrons and antenna of the S-band transmitter. After carrying out the calibration processes, we found that the look-up table in the control program is not properly linearizing the output of the power detectors. (These detector operate at intermediate power levels, so they are not simple peak voltage detectors nor average power detectors). This improper linearization is enough to explain why the sum of the power reading from the two klystrons fails to equal the antenna power reading.

While testing the arc detector circuits, an integrated circuit was accidentally damaged. As soon as the new part arrives we will devise a proper set-up procedure for these detectors, in which we measure the analog voltages from the photo detectors to set the threshold at the proper level.

I have received a passport and visa and have made travel arrangements to attend the ALFA acceptance tests in Australia in March We are looking at the interface requirements to control the rotation of the receiver assembly, in order to be prepared when it arrives in April.

To: Edgar Castro

From: Jon Hagen

Date: Feb 17, 2004

Subject: Week of Feb 9, 2004

Generated a new voltage-to-power table for diode detectors used for forward power measurement at the S-band transmitter's Klystron 1, Klystron 2, and antenna directional couplers. With this new table installed in the control program, the antenna power agrees with the sum of the two klystron powers.

The non-functioning arc detector (a redundant arc detector on one of the klystrons) was tested in the lab. Its op amp circuit works properly, but the photo diode in this channel is marginally different than the diode in the working channel. We have ordered replacement diodes. However, the circuit design is quite critical; the diode is followed by amplifiers with a total voltage gain of about 3000. The board

has no bias offset adjustment provision. Once a new diode has been installed, we will probably add trim pots for both channels.

We are trying to get Continental Electronics to provide us with the original schematics and instruction manual text on disks so that we can better update and maintain this documentation. They say this will involve considerable work on their part. If their quote is too high, we may be able to scan our old hard copies - or have it scanned by one of the companies that specialize in this work.

Designed the digital control unit needed to replace our 430 MHz driver amplifier with the recently acquired solid state power amplifiers from SRI. We also purchased a suitable dc power supply for these amplifiers and will add a suitable external capacitor bank to provide the required peak current of about 77 amps.

To: Edgar Castro

From: Jon Hagen

Date: Feb 24, 2004

Subject: Week of Feb 16, 2004

Looked into S-band transmitter's calorimetric power metering circuit. Flow is measured by sensing the differential pressure across an orifice plate. The accuracy of the flow measurement is supposed to be better than +/- 1%. The temperature at the ends of the waster load is measured by platinum RTDs (resistance temperature detectors). Why not a thermocouple pair? The temperature difference should be accurate to at least 1 Centigrade degree. The electronic unit for the RTDs had been damaged, probably by lightning, but was replaced and seems to be working correctly. I think we can assume the calorimetric measurement is currently the most accurate, and that we should adjust the scale factors for the directional couplers accordingly. However, one thing remains to be checked; the flow meter is a programmable electronic unit. A hand-held programmer unit us used to set the scale and to select whether the output is proportional to the differential pressure or to the square root of the differential pair (which is what is needed for operation with the orifice plate). We don't have a programmer unit, but may be able to determine experimentally that the square-root option has been selected. The two spare waveguide switches have been dismantled and cleaned. New ball bearings have been ordered.

A new photo diode was installed in the non-functioning S-band klystron arc detector, together with a trim pot circuit to adjust the amplifier offset. The circuit works again, but is as sensitive to drift as it always was. To avoid the need for frequent adjustments, the amplifiers following the photo diodes need to be modified to have ac rather than dc coupling; arcs are a sudden occurrence.

I canceled my plans to go to Australia for the final testing of the ALFA receiver, as the schedule now calls for the unit to be opened, displayed, and inspected upon arrival at the Observatory. The originally scheduled noise testing at Parkes had also been eliminated.

With Bill Sisk, I've drawn up plans for totally shielded enclosures for the ALFA fiber optic transmitters.

A prototype can be machined in Ithaca for testing here at Arecibo. These will be used eventually when we run the unconverted L-band signal all the way to the control room.

William Iguina is assembling the control unit for the solid state amplifiers that are to replace the old IPA (driver amplifier) in the 430 MHz Transmitter.

To: Edgar Castro

From: Jon Hagen

Date: Feb 27, 2004

Subject: Week of Feb 23, 2004

Updated the IF/LO block diagrams to include recently added filter options and assorted

other attenuator and port assignment changes. Distributed these drawings in PDF format.

Studied the S-band transmitter control software.

Talked with Bill Sisk about putting together an automatic receiver chain spread sheet maker program. The user would click on successive units from block diagrams, or simply key in a list of ID numbers for the successive elements in his receiver chain. The spread sheet program would identify each link in the chain, access the file (or spread sheet locations) containing its noise and dynamic range parameters, and enter them sequentially in a new area of the spread sheet. The completed spread sheet would show the overall system temp, and the dynamic range.

Wrote a memo explaining the operation and interaction of Breaker, the Vacuum contactor , and the Emergency Off Chain the S-Band Transmitter.

Kurt Kabelac at the Ithaca Lab is machining the prototype shield box for the ALFA fiber optic transmitters.

William Iguina is within two or three days of finishing the control unit for the solid state amplifiers that are to replace the old IPA (driver amplifier) in the 430 MHz Transmitter. This chassis will also contain three large electrolytic capacitors to allow pulsed operation of the amplifiers.

Prepared a talk to give on Monday to the group of visiting EE faculty members and students coming from the University of Colorado with Prof. Zoya Popovic.

To: Edgar Castro

From: Jon Hagen

Date: Mar 15 , 2004

Subject: Weeks of Mar. 1 and Mar. 8, 2004

Finished the control box for the new IPA (driver amplifier) for the 430 transmitter. Bench tested one of the solid state amplifier modules, which worked as specificied. Mounted both amplifier modules, control unit, power supply, and blower in a rack cabinet.

Designed a power combiner for these amplifiers, a circular branch line coupler and sent the drawings to the Ithaca lab for fabrication. However, first tests indicate that a single amplifier module will be sufficient to drive the two klystrons in the final amplifier.

Received the completed prototype shielded box from Ithaca. Installed the fiber optic transmitter. Bill Sisk tested the unit and found it totally RF tight. Meanwhile, we are building a new RF tight enclosure around the ALFA converter box. This should prove successfull, in which case the individual shields for the fiber optic transmitters would be used for a 'phase 2' upgrade.

Prepared a 7-question written test which can be administered to candidates for the RFI engineering position.

To: Edgar Castro

From: Jon Hagen

Date: Mar 26, 2004

Subject: Weeks of Mar. 15 and Mar. 22, 2004

The new IPA (driver amplifier) for the 430 transmitter has been in operation for two weeks with no problems. When the upcoming multi-day run is finished, we will move the old IPA to the warehouse.. We will also check the tuning of the klystrons, now that the wide-band IPA is in use.

Fabrication of the circular branch line coupler was completed in Ithaca and that unit is in shipment.

This unit will allow us to use both solid state driver modules at once, to provide adequate drive when the klystrons are tuned for maximum bandwidth rather man maximum gain.

The old oil-filled klystron test stand was removed from the transmitter room and stored in the transmitter warehouse. This unit had not been used in many years. The newly freed space can be used for the ALFA testing.

All the water cooling hoses on the 430 MHz transmitter are being replaced. The forty year old hoses have finally become brittle.

We are having an outside company scan all the S-band transmitter schematic diagrams in order to maintain and update this documentation in the computer. The cost is modest: forty-five cents per drawing.

Assisted in designing a outer shielding box for the ALFA post-amp/mixer chassis. The finished unit was then tested in a noisy environment and the increased shielding proved adequate.

Wrote a memo for Bill Sisk to help resolve a question concerning spectral analysis data processing.

Designed a VSWR meter which will be installed in the console of the 430 MHz transmitter to provide a continuous read-out of the reflected power in the 1500 ft waveguide run.

To: Edgar Castro

From: Jon Hagen

Date: April 2, 2004

Subject: Week of March 29, 2004 (4 days, Monday was a vacation day).

The circular branch line coupler arrived from Ithaca. Initial testing showed that the center conductor was shorted to ground. We opened the unit and enlarged the clearance around the center pins of the coaxial connectors (a dimension I'd failed to call out on the drawings). The unit then performed as expected.

We hope to get at least one more solid state IPA from SRI, to keep as a spare. The old IPA will be moved to the warehouse.

Expanded the spectral analysis memo I wrote last week and sent copies to Phil, Desh, and Bill Sisk, and made a PDF version to put on the web.

We realized that the now-surplus SETI trailer is extremely well shielded and could be used to replace our old shielded room. We can move this trailer to the area between the 430 MHz transmitter cooling pad and the a.c. power distribution pad, with its entrance end connected to the lab wall where Jose Vives currently sits. The trailer is narrow enough that the cable trench and cable trays would not have to be touched. This would provide a shielded room two to three times the size of the old shielded enclosure and would finally clear the entrance to both overhead doors of the transmitter room. The old shielded room would removed, leaving the large corner room available to provide more bench space.

To: Edgar Castro

From: Jon Hagen

Date: April 19, 2004

Subject: Weeks of April 5, 2004 and April 12, 2004.

A failed test bulb in the S-band Transmitter's arc detector left us with no spares. Continental Electronics had none in stock, but we manager to buy bulbs from an alternate supplier (at 1/3 the price) and now have the arc detectors on both klystrons working again. We are waiting for information from CPI (Varian) as to whether we can modify the arc detector circuits to use ac coupling, so they won't be as critical to align and maintain.

After Lynn Baker and Mike Nolan did the survey work to locate the focal point for the ALFA receiver, Phil Perillat and I marked the rotary floor for the cut out and the position of the mounting wedge.

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Gathered together the original schematics for the motor control of the platform-mounted 430 MHz waveguide power divider. Redesigned this control system to clean it up and to use a conventional motor rather than the old Slo-Syn stepping motor.

Failed to locate any supplier of 1 3/4" cooling hose to replace the failing 20-year old hoses on the 430 MHz transmitter. Ordered copper pipe which we will use to sleeve the present nipples, to use them with 2" hose.

To: Edgar Castro

From: Jon Hagen

Date: April 30, 2004

Subject: Weeks of April 19, 2004 and April 26, 2004 (including 4 days of vacation)

The installation of the ALFA receiver has affected the dynamics of the rotary floor drive system. This system has long been in need of review and documentation. I drew a schematic to understand and document the way the Kollmorgen torque bias card manages to coordinate the torques of the two drive motors, which are individually set up as velocity servos, though obliged to move at the same rate. We should consider installing an analog monitoring jack in the control room where we could sense the velocity of the floor. The control system sends back position and velocity information only once per second .

Had a teleconference with Ross Wilcox and Jim Topping at CPI (Varian) regarding the arc detector circuits used in our S-band transmitter. My questions were: 1. Can the arc detector amplifier chain be a.c. coupled, or is there some kind of klystron window glow that requires d.c. coupling? and 2. If Varian requires that the tubes be operated with arc detectors, why doesn't Varian market suitable detectors or at least provide an application note for their design? I wasn't able to get definite answers to either question. They acknowledged that they have a highly refined arc detector, designed by Jim, but would have to consult with their legal department before divulging this design to us. (We might expect they would also contact their sales department). They did promise, however to send me information on the photo-diode used in their circuit.

Repairs have been made to the shipping crate for the non-working S-band klystron so that it can be sent back to CPI.

We received the copper tubing needed to enlarge the pipe nipples so that we can use new 2" diameter cooling hoses with our 430MHz klystrons. One of the 4-inch hoses in the S-band transmitter also worked its way loose. It was reconnected and the system refilled without further problems, but we are getting quotations to replace these large, ten-year-old 'Brew-Master' hoses.

To: Edgar Castro

From: Jon Hagen

Date: June 18, 2004

Subject: Week ending June 18, 2004

The RF attenuator failed in the exciter of the S-band transmitter, causing the loss of the first of three runs. A new attenuator is on order. Meanwhile, we have jumped around the failed component and are controlling the level (to within 1 dB) by adjusting the level of the synthesizer.

The 430 transmitter failed to come up due to a short in the interlock chain (inadvertently created when

cables were re-dressed after cleaning out cables used with the old IPA). During troubleshooting, we found that the coil of the large contactor for the magnet power supplies is powered by a line diverted from the interlock chain. We will install an auxiliary relay to avoid overloading the interlock chain, which passes through many low current devices. We have now received all the parts needed to replace all the cooling hoses on the 430 transmitter.

The SETI trailer has been cleaned out to become our new shielded room. The shielded racks (all aluminum!) have been removed and the computer floor is being taken up. A new floor, work benches, and a split air conditioner will be installed. Junk has been removed from the ATR shack and it is now in good order.

The Mark 5 VLBI equipment arrived - without a shred of documentation (no surprise). Tapasi has several memos from a summer workshop what explain, more or less, how this equipment is to be mated to our VLBA-4 terminal.

As of Friday afternoon, we are still troubleshooting a failure in the 430 MHz CRR1 receiver, needed for runs tonight and the next two nights, and trying to cool down the S-band Low receiver (which is needed tonight and for the next six nights). Apparently the refrigerator in the S-band receiver has a bent displacer cylinder, which our technicians been able to make work - until now. We have been handicapped today by having Ganesh and Ernesto out sick.

To: Edgar Castro

From: Jon Hagen

Date: July 2, 2004

Subject: Week ending July 2, 2004

A new RF attenuator was installed in the exciter of the S-band transmitter, replacing the unit that failed three weeks ago.

All the cooling hoses in the 430 MHz transmitter, except those on the dummy and waster loads, have now been replaced. These last hoses should be changed in another week. We are installing the oil lines to the outdoor oil cooler.

The S-band cooling hoses were replaced in the cable machine. These hoses, like the 430 hoses, had become brittle and stiff. The UPS for the S-band dome control unit was replaced.

The Mark 5 VLBI equipment has been mounted in a rack and is ready for testing.

The warehouse for the 430 MHz klystrons has been put in good order. The klystrons have been arranged for removal in the order we expect to use them. They are on vac-ion pumps and the vacuums will be monitored.

Jorge Rodriguez is putting more order in the Vertex pointing system PLC software - adding variable names, and figuring out program flow and control algorithms. This work must be done prior to a changeover to a new control computer of whatever architecture we finally select.

To: Edgar Castro

From: Jon Hagen

Date: July 16, 2004

Subject: Weeks ending July 9 and July 16, 2004

Klystron B, in the 430MHz transmitter, failed dramatically, leaving a belt of charred paint in the area of the output cavity. The crowbar had fired and the vac-ion current for this tube soared. The transmitter was brought up slowly, to recondition the tube, but the vacuum did not improve. We presume that the charring occurred during this time. (The burned paint is on a metal shroud, about an inch from the actual klystron body, so the body must have become extremly hot ). The companion tube had been on its last legs for several months, so both tubes were replaced. The replacements are L5773, the 'new' higher efficiency klystrons. As the new tubes were being conditioned with high voltage, several rectifier stacks failed. These were repaired. At least one long-defective stack was also repaired, as the beam voltage ripple is now much less than it has been. We should implement a monitor for the beam ripple so that any rectifier failure is immediately obvious.

The azimuth encoder failed and was replaced. This is generally a job that takes several hours. It seems feasible and worthwhile to install back-up encoders. These would be constantly monitored, both to ensure that they are working and to measure their offsets from the working encoders. When an encoder fails, we would be able to switch immediately to the back-up encoder by a simple computer command from the control room.

To: Edgar Castro

From: Jon Hagen

Date: Aug 2, 2004

Subject: Week ending July 30, 2004

The last of the cooling hoses were replaced in the 430 MHz transmitter and tested for leaks. Several defective interlock switches were also repaired. The transmitter failed on it's the next run, but not because of anything disturbed during these repairs; the floating deck of the beam modulator stuck "on" due to the failure of a 4-400 vacuum tube.

We have received high voltage insulating structural members with which to rebuild the bleeder resistor tower. Over the years the old tower has been progressively damaged by corona, arcing, occasionally catching on fire. We have also received digital water temperature and oil temperature displays which will be installed on the on the console of the 430MHz transmitter.

I gave Sixto a 'final' version of the floor plan for the remodeling of the Electronics Area in Building 1.

The azimuth encoder failed and was replaced. This is generally a job that takes several hours. It seems feasible and worthwhile to install back-up encoders. These would be constantly monitored, both to ensure that they are working and to measure their offsets from the working encoders. When an encoder fails, we would be able to switch immediately to the back-up encoder by a simple computer command from the control room.