VLBI System Documentation

Mark IV Field System

VLBA Hardware Setup

J. C. Webber, W. E. Himwich

Interferometrics, Inc. and NVI, Inc./GSFC

Operations Manual

NASA/Goddard Space Flight Center Version 8.2

Space Geodesy Project September 1, 1993

• 1.0 Introduction
• 2.0 I/O Connections
• 3.0 Powering Up
• 4.0 Computer Communications
• 4.1 Establish MCB Communications
• 4.2 Set Field System Time
• 5.0 Setting the Formatter Clock
• 6.0 I.F. Distributor
• 7.0 Baseband Converters
• 8.0 Formatter
• 9.0 Recorder
• 10.0 Data Quality Analyzer
• 11.0 Track Assignments

This manual describes general setup for VLBA equipment. Portions of the manual are extracted from the preliminary version of the VLBA Data Acquisition Terminal: Operating manual written by John Webber. Refer to the Interferometrics technical manuals (white notebooks) for detailed documentation, specifications, and drawings for each module.

Refer to the companion Field System manuals in this volume for system setup and system tests: Mark III Hardware Setup and System Setup and Tests. The Mark III manual covers the Mark III modules and I/O connections. The system manual is applicable to either Mark III or VLBA equipment.

There are two racks of VLBA equipment. The recorder rack is often referred to as REC (for RECorder rack) and the electronics rack is often referred to as DAR (Data Acquisition Rack).

The I/O connections to be made to the DAR and REC are the following.

5 MHz:

The maser 5 MHz reference at nominal +13 dBm is required and must be connected to the 5 MHz input on the rear panel of the DAR.

1 pps:

The 1-second tick from the maser or GPS receiver or what have you is connected to the rear panel of the DAR. The station timing module accepts either a rising or falling edge as the reference, and the cable should be connected to the + or - input BNC, respectively. In order to synch the station timing module, hold the switch in long enough for one pulse to pass through; then check for synchronization using an oscilloscope connected to the known 1 pps and to the Station Sync front panel output on the 32 MHz synthesizer module. The SYNC output pulse should also be present, and it must lag the other front panel output by 36220 nsec.

IF inputs:

The four IF inputs A, B, C, and D should be connected on the rear of the DAR. There should be no signals below 500 MHz or above 1 GHz in order to prevent spurious mixing products from appearing in the system.

Interconnection between racks:

The two 40-pin and one 20-pin cables should connect the formatter and recorder via the panel connectors. In order for the bit synchronizers to work in drives with the Mark III bit synchronizers, the X21 output from the DAR must be connected to the REC. This is not necessary for the new monitor board. There are 5 MHz and 1 pps outputs provided from the DAR for the REC, but these are not strictly necessary in the field; they are intended primarily to aid synchronization of tapes at the correlator. Finally, the MCB cable from the computer should go either to either the DAR or the REC and then via jumper to the next rack. If you have any more equipment on the MCB, it goes in the daisy chain as well. Strictly speaking, the MCB should be terminated, but it seems to work just fine with no termination in the short runs usually used.

Power up the DAR with the front panel switches on the power supplies. The power supplies are located at the top of the rack.

After power up, you should also reset the 1 pps (see previous page), then reboot the formatter CPU (see the formatter section of this manual).

The power switch for the REC is on the front panel. You should reboot the recorder's CPU (see the recorder section of this manual).

The Field System computer controls all communications with the VLBA rack and recorder. When the equipment is powered on, the modules come up in a known default state with "reasonable" values. Initialization of the communications in not normally required.

4.1 Establish MCB Communications

The communications with the MCB (monitor and control bus) can be tested by attempting to communicate with some of the modules using the Field System. Refer to how to start the Field System in the Operators' Reference manual. Send a command to read back a baseband converter, bbc01, to see if communications are working. If no response is received, check the following:

- The ribbon cable between the computer and the DAR or REC must be connected. One end is connected to the rear of the electronics rack and the other end is connected to the MCB interface box.

- The MCB interface box must be installed properly. The output cable goes to the equipment; the input cable comes from one of the ports on the Digiboard mux panel.

- The port on the mux panel must correspond to the device name given in the dev.ctl control file.

- The mcbad.ctl control file must be set up properly with addresses for the modules you have at the station.

4.2 Set Field System Time

Once the Field System is running, set the formatter clock to U.T. using the program fmset (see next section). Then set the Field System time using program setcl. The program first reads the formatter clock to obtain the correct time. The computer clock is not actually changed, rather the Field System maintains an offset between the formatter clock and the computer clock. The time that is logged for commands and responses and monit's time reflect the Field System's clock as it was last synchronized with the formatter clock.

After setting the formatter time, you must set the Field System time by issuing the SNAP command sy=setcl offset. Refer to the manual on setcl and the description of the time.ctl control file in the Control Files manual for a detailed explanation.

The formatter clock must be set to UT using the station reference clock. The formatter's internal timekeeping must be brought into synchronism with the station reference clock.

In order to insure that the formatter is set up properly, do things in this order:

1. Synchronize the station timing module in the rear of the rack by holding in the pushbutton for longer than 1 second. This synchronizes the formatter to 1 pps.

2. RESET the formatter from the red front-panel pushbutton. This reboots the formatter's CPU.

3. Set the date and UT in the formatter clock using the fmset program. The Field System must be running and communications with the DAR must be established (see previous section). To run fmset, type Alt-T if you have the standard window menus set-up, or open a new window and at the shell prompt type fmset. The display shows the formatter time, the Field System time, and computer time. Simple instructions for changing the time are included on the screen. Refer to the fmset manual for more explanation.

4. Once the date and time have been set in the formatter clock, you should double check the seconds. If your rack displays the least-significant seconds digit, you can compare it to your station clock. The display should change synchronously with the station clock. If your rack does not have the seconds display, you will only be able to compare the fmset display to your station clock.

There are two I.F. distributors in a standard VLBA rack. They are referred to as IF distributors 1 and 2. Each distributor has two IF input channels. Channels A and B are on IF distributor 1 and channels C and D are on IF distributor 2.

Normal setup for IF distributor channels for S/X geodetic stations is:

Channel A X-band IF signals that have been upconverted.

Channel C X-band IF signals that have not been upconverted. This corresponds roughly to Mark III IF3, the upper part of the wider band now being used at X-band.

Channel B S-band

There is a separate command for each IF distributor module since they can be set up independently. Normally the attenuators should be set to 0 so that they can be used for total power radiometry. The following commands would set up the modules:

ifdab=0,0,nor,nor

ifdcd=0,0,nor,nor

There are 14 baseband converters in VLBA racks set up for geodetic experiments. Both the LO frequency for baseband conversion and the IF input source are specified when you command the BBC.

An example for a geodetic setup is the following. To set up BBC number 1 for X-band upconverted (IF channel A) input:

bbc01=612.89,a,2,2

This command also sets up the BBC for 2 MHz bandwidth on both USB and LSB.

The formatter is set up with the form Field System command. Example:

form=c,4

Refer to John Webber's memos and other technical memos about the recorder in the manufacturer's technical manuals provided with the recorder.

The initial Field System implementation of recorder commands for the VLBA makes heavy use of existing code as far as possible. This means that we take advantage of almost none of the programming done to make the recorder controller smarter. Later versions of the Field System will make use of the better control.

There are two basic Field System commands that control the recorder: rec and tape. Examples of the use of each command follow.

Use the rec command to control the various actions of the recorder such as loading and unloading tapes or going to a new footage count. The command

rec=load

would load a freshly-mounted tape into the vacuum columns. If you need to spin the tape to a new footage count for the next observation, use the command:

rec=2550

If you had a power failure and need to set the footage counter approximately correctly, the recorder can determine this for you. Use the following commands to move the recorder forward a few feet and set the footage:

st=for,120,off

(run for a few seconds)

et

rec=feet

The recorder will determine the supply and takeup reel packs and set the footage counter.

The tape command is similar to the Mark III command. In particular the monitored footage count appears in the same location within the response which provides compatibility with programs that read log files at the correlator. You can turn on the low tape sensor with the command tape=low.

The data quality analyzer (DQA) is a formatter sub-module. It extracts phase calibration signals, measures parity error rates, and measures re-synch rates.

You can use the dqa command to measure and record phase cal amplitude and phase. The formatter must be set up and the appropriate groups enabled. Then issue these sample commands:

repro=byp,1,2

dqa=1

dqa

The response will display the phase cal amplitude and phase for tracks 1 and 2. Refer to the SNAP Commands manual for a description of the response. Refer to the dqaodd and dqaeven procedures in the Standard Procedures manual.

The tables in this section list the connections between BBC video outputs, formatter tracks, formatter A/D tracks, formatter pins, and recorder tracks. These tables are for the Interferometrics rack sampler wiring. The NRAO VLBA racks have different wiring.

The standard Mark III track assignments are found in tables in the System Setup manual.

Note that throughout the Field System SNAP commands, Mark III track numbers are used for both Mark III and VLBA control.

Sampler Outputs to Formatter A/D Numbers (Interferometrics racks)
VLBA mode			MK3 mode		FRM
BBC	SSB	BIT	BBC	SSB	A/D
1	U	S	1	U	3
1	U	M	2	U	2
1	L	S	3	U	1
1	L	M	4	U	0
3	U	S	9	U	11
3	U	M	10	U	10
3	L	S	11	U	9
3	L	M	--	-	8
2	U	S	1	L	7
2	U	M	2	L	6
2	L	S	3	L	5
2	L	M	4	L	4
4	U	S	9	L	15
4	U	M	10	L	14
4	L	S	11	L	13
4	L	M	--	-	12
5	U	S	5	U	19
5	U	M	6	U	18
5	L	S	7	U	17
5	L	M	8	U	16
7	U	S	12	U	27
7	U	M	13	U	26
7	L	S	14	U	25
7	L	M	--	-	24
6	U	S	5	L	23
6	U	M	6	L	22
6	L	S	7	L	21
6	L	M	8	L	20
8	U	S	12	L	31
8	U	M	13	L	30
8	L	S	14	L	29
8	L	M	--	-	28

BBC Outputs to FRM and REC Tracks -- Mode A -- (Interferometrics racks)
BBC		REC track	MK3 track	FRM track	A/D #	FRM pins
1	U	4	1	17	3	J02	5,6
1	L	18	15	24	7	J02	19,20
2	U	5	2	1	2	J01	5,6
2	L	19	16	8	6	J01	19,20
3	U	6	3	18	1	J02	7,8
3	L	20	17	25	5	J02	21,22
4	U	7	4	2	0	J01	7,8
4	L	21	18	9	4	J01	21,22
5	U	8	5	19	19	J02	9,10
5	L	22	19	26	23	J02	23,24
6	U	9	6	3	18	J01	9,10
6	L	23	20	10	22	J01	23,24
7	U	10	7	20	17	J02	11,12
7	L	24	21	27	21	J02	25,26
8	U	11	8	4	16	J01	11,12
8	L	25	22	11	20	J01	25,26
9	U	12	9	21	11	J02	13,14
9	L	26	23	28	15	J02	27,28
10	U	13	10	5	10	J01	13,14
10	L	27	24	12	14	J01	27,28
11	U	14	11	22	9	J02	15,16
11	L	28	25	29	13	J02	29,30
12	U	15	12	6	27	J01	15,16
12	L	29	26	13	31	J01	29,30
13	U	16	13	23	26	J02	17,18
13	L	30	27	30	30	J02	31,32
14	U	17	14	7	25	J01	17,18
14	L	31	28	14	29	J01	31,32

BBC Outputs to FRM and REC Tracks -- Mode B -- (Interferometrics racks)
BBC		REC track	MK3 track	FRM track	A/D #	FRM pins
1	U	4,5	1,2	17,1	3	J01,J02	5,6
1	L	18,19	15,16	24,8	7	J01,J02	19,20
3	U	6,7	3,4	18,2	1	J01,J02	7,8
3	L	20,21	17,18	25,9	5	J01,J02	21,22
5	U	8,9	5,6	19,3	19	J01,J02	9,10
5	L	22,23	19,20	26,10	23	J01,J02	23,24
7	U	10,11	7,8	20,4	17	J01,J02	11,12
7	L	24,25	21,22	27,11	21	J01,J02	25,26
9	U	12,13	9,10	21,5	11	J01,J02	13,14
9	L	26,27	23,24	28,12	15	J01,J02	27,28
11	U	14,15	11,12	22,6	9	J01,J02	15,16
11	L	28,29	25,26	29,13	13	J01,J02	29,30
13	U	16,17	13,14	23,7	26	J01,J02	17,18
13	L	30,31	27,28	30,14	30	J01,J02	31,32

BBC Outputs to FRM and REC Tracks -- Mode C -- (Interferometrics racks)
BBC		REC track	MK3 track	FRM track	A/D #	FRM pins
1	U	18,19	15,16	24,8	3	J01,J02	19,20
2	U	4,5	1,2	17,1	2	J01,J02	5,6
3	U	20,21	17,18	25,9	1	J01,J02	21,22
4	U	6,7	3,4	18,2	0	J01,J02	7,8
5	U	22,23	19,20	26,10	19	J01,J02	23,24
6	U	8,9	5,6	19,3	18	J01,J02	9,10
7	U	24,25	21,22	27,11	17	J01,J02	25,26
8	U	10,11	7,8	20,4	16	J01,J02	11,12
9	U	26,27	23,24	28,12	11	J01,J02	27,28
10	U	12,13	9,10	21,5	10	J01,J02	13,14
11	U	28,29	25,26	29,13	9	J01,J02	29,30
12	U	14,15	11,12	22,6	27	J01,J02	15,16
13	U	30,31	27,28	30,14	26	J01,J02	31,32
14	U	16,17	13,14	23,7	25	J01,J02	17,18