To: File (c:\hagen\wpfiles\vlbi\vlbistds.wp6)

From: Jon Hagen

Date: 4-19-00 6-16-00, 6-19-00, 8-03-00

Subject: VLBA and VLBI Formats

NRAO Mark I (used 1967-1978): Ampex TM-12, sample rate 0.72 Mbits/sec.

tape time 3.2 minutes

NRAO Mark II used 1971-19798: sample rate 4 MBits/sec

tape time: 190 minutes with Ampex BR660C, 64 minutes with IVC800,

246 minutes with RCA VCT500

Canadian 1971 - ? 8 Mbits/sec, tape time 64 minutes with IVC 800

VLBA, from VLBA Tech Report No. 15 (Rev. A), A.R. Thompson,

March 10, 1993 "An Intro to the VLBA receiving and Recording System"

Four antenna cables allow reception on 2 frequencies, each with 2 polarizations.

Four IF distributor modules provide 8 output spigots for each of these 4 signals to supply the baseband converters. These IF signals are in the range 500-1000 MHz.

There are 8 baseband (ssb) converters. Each converter has a USB output and a LSB output to produce a total of 16 baseband signals with bandwidths switchable over 16MHz, 8MHz, .... 1/8 MHz, and 1/16 Mhz. Each converter has its own LO, tunable over the 500-1000 MHz range.

The maximum total bandwidth is therefore 16 x 16 = 256 MHz.

Two sampler modules, each with 8 samplers, digitize the baseband data signals into either 1-bit or 2-bit representations. The maximum output data rate occurs when all 8 samplers are clocked at 32 MHz with 2-bit digitization: 2 (usb and lsb) x 8 samplers x 32 MHz x 2bit = 1024Mbits/sec.

The formatter takes the 16 digital data streams and produces data streams for the recorder, which has 36 heads: 32 for data and 4 for system use. The maximum recording rate is 8 Mbits/sec per track x 32 tracks = 256 Mbits/sec. TWO recorders are used in parallel for a data recording capacity of 2 x 256 = 512 Mbits/sec. Thus the maximum bandwidth, 256 MHz, can be handled if one-bit sampling is selected. (Note that this 256 MHz is total bandwidth, e.g. 128 MHz on each of two polarizations or 64 MHz on each of two frequencies and two polarizations).

The formatter allows a wide selection of format parameters including length of a frame, length and definition of the header, whether or not data are lost when the header is written, multiplexing or de-multiplexing of data streams onto recording tracks, implementation of longitudinal parity, cross-track parity, a CRCC correcting code, a track (or "barrel ") roll of the data streams relative to the recording tracks, and other features. Std format for VLBA observations is defined in Spec. A56000N003. The Mark III VLBI format is also commonly implemented with the VLBA formatter. The formatter was designed by J. I. Levine of Haystack Observatory.

Usually a single recorder is used, running at 128 Mbits/sec. This limitation is so that the average recording rate is not greater than the playback rate of the correlator (which is 256 Mbits, with one playback recorder per antenna). (Why isn't the usual single recorder used, then, at 256?)

Thus the "usual" operation provides a bandwidth of ½ x 128 = 64 MHz.

The tape transport used for all versions of Mark III and VLBA is Honeywell Model 96. Tape is guided by the rear edge which is biased into the 'precision plate' by the action of the vacuum.

Mark III

Ref: "Mark III VLBI Data Acquisition Terminal"

NASA Instruction manual, Jan. 1982

Table I, page SYSTEM-16

Ampex 797 (old) Ampex 721 (new) 1-inch instrumentation tape

28 tracks according to IRIG 1067-73 standard

(no head shifting, so transverse density is 28 tracks

Longitudinal density 33,333 bits per inch on each track

Max tape speed: 135 inches/sec (page SYSTEM-8) so maximum

recording rate is 135 x 33,333 x 28 = 126 Mbits/sec for formatted data

(4Mpbs x 28 = 112 Mbps at nom. max speed of 135 "/sec).

System uses 14 video converter modules. "Each module may contain internal low pass filters from 0.125 to 4 MHz although typically on the 2 MHz filter is installed". Each converter has both I and Q outputs of 0-2 MHz. These are sampled with 1-bit samplers at the Nyquist rate of 4 MHz. Thus the total raw data rate in bits/second is 14 x 2 x 4MHz = 112 M bits/sec.

How much RF bandwidth? The RF bandwidth of each converter is 4MHz, i.e. +/-2MHz so

the total bandwidth is 14 x 4 = 56 MHz.

Mark IIIA

Ref: Mark IIA/IV/VLBA tape Formats, Recording Modes, and Compatibility

Alan R. Whitney, MIT Haystack :The Mark IIIA, VLBA, and Mark IV VLBI data acquisition systems are all based on the Metrum (formerly Honeywell) Model 96 transport using 1'' wide reel-to-reel tape."

Tape drive info from"Hinteregger, Rogers, Cappallo, Webber, Petrachenko, and Allen,

"A high data rate recorder for astronomy, IEEE transactions on magnetics, may 91" (included as appendix 4 in VLBA Tech. Report No. 15 (RevA), "intro to VLBA... by A.R. Thompson:

"The first version of the wide-band VLBI recorder became operation in '79 and is known as Mark III. Nom. maximum of 112 Mbits/sec (224 at the non-used double speed mode) but requires large amounts of tape because it used fixed heads to record 28 ea. 635- m-
wide tracks across inch-wide tape, each with a longitudinal density of 1.31 fr/um or 33.3 kfrpi.

A higher density 1985 version, Mark IIIA, involved a "density upgrade" moveable head kit for the Mark III recorders. Area density of recording increased by more than an order of magnitude by reducing the track width from 635 to 38 um. Modern video tape and narrow-track head stacks and head stack positioning systems developed by Haystack are used. Mark IIIA machines record a total of 336 tracks, 28 at a time in 12 passes, each lasting 800 sec. Thus one 2750-m tape lasts 160 min which recording at 56 MHz bandwidth (112 Mbits/sec at one bit per sample) and holds about 1012 bits. There are presently (1991) over 30 machines worldwide. Mark IIIA is just Mark III with the narrow-track moveable head stacks.

For the VLBA a new version has been developed. The same head stacks and positioners are used but with new electronics and provision for the support of four 36-head stacks. The same head stacks are used for read or write, and the tape is bulk erased between recordings. The VLBA recorders have been tested using a longitudinal density of 2.25 fr/um (58.15 kfrpi). 448 data tracks plus 56 system tracks are recorded in 14 passes, each lasting 50 mi, for a total record time (at 128 Mbits/sec) of 12 hours on a 14-inch diameter reel of 1-inch wide 12um thick D1 equivalent tape.

"Mark III record lengths are 5 msec (20,000 bits). In the mark II system, which uses video recorders, the data are recorded with a self-clocking code, while in the Mark III system, which use instrumentation recorders, the data transitions themselves serve as the clock". (from Thompson, Moran, & Swenson).

Mark IV

Ref: Mark IIA/IV/VLBA tape Formats, Recording Modes, and Compatibility

Alan R. Whitney, MIT Haystack: Also Rev 1.6 of "Mark IV Tape Format, Recording Modes and Compatibility, Alan R. Whitney, MIT Haystack Observatory, 4 June 1995.

The Mark IIIA, VLBA, and Mark IV VLBI data acquisition systems are all based on the Metrum (formerly Honeywell) Model 96 transport using 1'' wide reel-to-reel tape."

"The mark IV is an upgrade to the original Mark IIIA system and was designed primarily for two purposes, 1) expansion of maximum data rate from 224 Mb/sec (double speed) to 1024 Mb/sec and 2) full compatibility with all VLBA channel-bandwidth and data-multiplex modes. For this purpose,

an entirely new formatter was designed for the Mark IV system, and modifications were made to BBCs and the tape transport.

The Mark IV system can record up to 64 simultaneous tracks (expandable to 128 tracks) at a max data rate of 16 Mb/sec/track (18 Mb/sec/track with parity) for a maximum total data rate of 1024 Mb/sec (expandable to 2048 Mb/sec by added another par of head stacks). In the Mark IV system, as in the VLBA system (but unlike the Mark IIIA system), data from a single video converter channel may be distributed to multiple tracks; conversely data from several channels may also be multiplexed onto a single track. Therefore, in order to completely understand the Mark IV tape format, we must understand both the format along a single track (longitudinal track format) and the format laterally across the simultaneously-written tracks (transverse track format).

The Mark IV uses two head stacks of 32 tracks each, for a max of 64 simultaneously.-written tracks on a tape. Data is written to these 64 tracks through a 64x64 cross-point switch which can be arbitrarily reconfigured according to 16 independent user-definable maps.

The Mark IV systems utilizes the Metrum Model 96 transport which has been heavily customized with headstacks, headstack-positioning capabilities and data electronics. Although the basic tape-moving part of the transport is nearly origninal, sig. mods have been made in the tape-path mechanical components in order to meet the req of the Mark IV system.

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Notes on what Arecibo is supposed to receive from Signatron

from meeting notes by Andy, 7-13-98 at Haystack (Andy, dan Smythe, Roger Cappallo)

Haystack terminology for Signatron system going to AO: "VLBA-4 and NOT a Mark 4 system. A VLBA-4 system is an upgraded VLBA recorder (1024 Mbps, expandable to 2048 Mbps,vs. 256 Mbps for VLBA) coupled to a Mark-4 formatter. Conversely, what Haystack calls a Mark 4 system contains an upgraded Mark-3 recorder. Design work was not complete for the Mark IV decoder; Dan Smythe thought that Haystack could loan us a Mark III decoder until the Mark IV decoder is available. (jbh: what's this, for testing?)

Original PO to Signatron Order Number A81403, req. no. 3273,

Account code U22 8381 5020 000 010, dated 28 May 98

$465,523.00 for materials for shipping point "as per attached"

1.	One VLBA Data Aquisition Rack wired for 8 baseband converters

2.	8 VLBA baseband converters (T122)

3.	1 5MHz Distributor (L121)

4.	1 32 MHz Distributor (L122) (used just for the 1pps circuitry - the "32 synth" is now included in the formatter.

5.	2 IF distributors (T121)

6.	1 Output rate distributor (D122)

Mark IV Decoder

9.	1 Mark IV formatter assembly 4711

10.	1 P105 power supply module

11.	2 P103 power supply modules

12.	2 P101 power supply modules

13.	1 VLBA Tape Recording System VLBA4-0010

plus 1 complete set of Electrical Schematics, Wiring Diagrams, and parts layout drawings for both the DAR and Tape Recording system.

Note that item 13 is listed as a "VLBA Tape Recording System" and not as an "upgraded VLBA Tape Recorder" and that item 9 is listed as a "VLBA formatter assembly" and not as a

"Mark IV" formatter. Note that no decoder module is listed.

Guarantee : "Signatron's standard 1-year guarantee" which is probably similar to the Interferometrics guarantee: 1-year against manufacturing defects (including firmware?) . As for the recorder, it carries the balance of Metrum's 1-year guarantee which began when the recorder was shipped to Interferometrics.

Purchase Order Change Notice, Aug. 27, '98 to PO A81403 or May 28, 98

Addition of items 1-12 attached, $4744 additional, bringing total to $470,267.00.

These 12 items (first 12 of 14; 13 and 14 are two power supplies) are to upgrade the race from 8 BBC capacity to 14 BBC capacity.

1. add an additional VLA bin

2. Add associated brackets, connectors, and blank panels

3 Add low profile cooling fan array

4 add power wiring to additional bbc locations

5 add coax connections from 5 MHz dis to additional bbc locations

6 add coax connections from 32 MHz dis to additional bbc locations

7 add connections to formatter from additional bbc locations

8 reconfig. coax wiring and new coax connections for IF distrib's to new bbc locations.

9 No item 9!

10. Add monitor control mux connections to new bbc locations

11. "An additional 5 MHz dist. must be added or the existing dist. has to be modified to add more buffer amp sections for the 6 additional bbc's."

12 "An additional 32 MHz dist. (1pps buffer sections only) must be added or the existing dist. has to be modified to add more buffer amp sections for the 6 additional bbc's."

List of deliverables in the VLBA-4 System:

2 six-ft racks (racks included in order)

Additional Purchase Order for dry air kit

PO A91282, 26 May 1999,

DRy Air Kit Addition 1ea. $4780.00

The original P.O. includes a payment schedule (prepared by Signatron). The final payment of 10% is after completion of acceptance testing. Signatron's original proposal (chosen by NAIC over proposals from Interferometrics and Allied Signal) states "Signatron Technology uses a Russian-developed software package for DAR System control and acceptance testing. We also use an NRAO software package (BBCTEST) for testing the baseband converters. In the past we have also used Ver 8.1 of the VLBA field system for test and control. " The Interferometrics proposal included "zero-baseline testing" wherein a tape is written and processed on a VLBI correlator.

Note that none of these purchase orders are contracts that include required delivery dates. Nor do they specify acceptance test procedures .

Change to VLBA-4

Paul Lane (Signatron) wrote Edgar Castro on 2 June 98, thanking AO for the award of the VLBA P.O. He said that he had been discussing the award with Haystack staff members and that they felt AO might be better served with a VLBA/4 DAR rack as other observatories involved with VLBI/VLBA will be switching to the MARK-4 formatters in the coming years. (The original style VLBA formatter would be replaced with a MARK 4 style Formatter. An additional module, a TTY Distributor "is also required". Hee offers this upgrade at no additional cost and awaits a decision from AO.

After a conference call, Signatron wrote a detail letter to Edgar on 9 July '98 detailing the upgrade. A decoder (2-rack readback) would be required (design is 95% complete at Haystack) but the added cost of the decoder will be offset by the elimination of the 2 sampler modules and the output rate synthesizer module.

Then Andy had a meeting at Haystack with Dan Smythe and Roger Cappallo on July 11, '98 to discuss the upgrade idea.

Seems an email approval must have been sent by Edgar to Paul Lane. Our VLBI terminal is therefore to be a "VLBA-4": an ungraded VLBA recorder and a Mark IV DAR.