Quick BCPM instructions

Adapated and updated from the GBT BCPM page by Ingrid Stairs, Frank Ghigo and Glen Langston.

Logging In
IF/LO
Observing
Miscellaneous including Sample Time Table
Troubleshooting

Logging In

Ssh as yourself to a computer that is known to the bcpm (eg, vortex or sadira).
Ssh from vortex/sadira to bcpm2 as bcpm2 (get password from Operator).
Optional. In general you do NOT need to do this -- writing to the pulsar area is standard practice:
1. Choose option "l" to start the normal Unix login.
2. "cd dat"
3. List "hardware.conf". If you want to add a new 'tape' data area on vortex, follow the next step. Otherwise make sure the "tape" line points to the desired data area.
4. If adding a new data directory: Edit "hardware.conf" and scroll to the bottom of the file. Change the "tape" line to read "tape /home/vortex/your_login/bcpm2/scratch 1 1 1" using the bjacoby and istairs lines as guides. You must have a world-writeable directory on the main GB system called /home/vraid2/scratch/your_login/bcpm2/ for this to work. Do not make a subdirectory called "scratch"; "scratch" is used as a temporary filename.
5. "cd .."
Select or type "ui" to start the User Interface, then hit "return" on "bcpm2" when prompted for a username. The usual BCPM windows will appear.

IF/LO Setup

Choose the right IF input! In the blue command-line window, type "setif 1" for 600/800/Lband, "setif 2" for 340/450/S-band and "setif 3" for 85-3.

The BCPM is connected to Converter Modules 4 and 8 (IF 1), Converter Modules 12 and 16 (IF 2) and 85-3 610 MHz (IF 3). These days (2006), we are pretty much always on "setif 1".

Astrid or config_tool will set up the entire GBT IF chain for the BCPM, using the following equations for setting up the Converter rack LO2 frequency. The BCPM input IF center frequency (F_{BCPM_Center}) is 400 MHz, so the Converter Module LO2 frequency (F_LO2) is set by the following equation:

F_LO2 = 10500 + F_{Optical_Receiever_Center} - F_{BCPM_Center} MHz

Different Receivers have different Optical Receiver output center frequencies (F_{Optical_Receiver_Center}).
For the S band system, the LO1 Sky frequency corresponds to 6000 MHz IF frequency:

F_{LO2_S} = 10500 + 6000 - 400 = 16100 MHz
For L band, the LO1 Sky frequency corresponds to 3000 MHz IF frequency: F_{LO2_L} = 10500 + 3000 - 400 = 13100 MHz
For Prime Focus 1, the LO1 Sky frequency corresponds to 1080 MHz IF frequency: F_{LO2_PF1} = 10500 + 1080 - 400 = 11180 MHz

Observing

A typical sequence is: Monitor scan, cal scan, data scan. Here are procedures for running each of these by hand.

Monitor Scan:

Type "monitor" in the blue tui window.

Answer the questions as prompted. Normal operation involves sampling power (not voltages), summing the polarizations, and using either 1.0 MHz/72 usec mode or 0.5 MHz/72 usec mode.

When on source or very close to it, hit "balance" on the IF Rack, making sure you are talking to the correct set of Optical Drivers (1/2, 3/4 for 600/800L-band; 5/6 and 7/8 for 340/450/S-band). Astrid blocks may already be set up to do this for you

(First obs at the frequency only) Check the powers and attenuators in the Convertor Rack (Rack A for PF, L-band; Rack B for S-band; always Convertor Modules 4/8 for the BCPM). The power levels should read about 0.1 (upper) and 0.15--0.2 (lower).

By now the BCPM should be displaying changing levels. If not (ie the I/O rate is 0 MB/sec), see Troubleshooting. In the blue command-line interface window, type "setpower". This will work well for the 0.5 MHz/72 usec mode. For the 1.0 MHz/72 usec mode, it's best to go to the convertor rack and subtract 1 dB of attentuation from each polarization after doing setpower.
Once happy with the power levels on the BCPM, type "abort" in the blue tui window.

Cal Scans and Data Scans:

Type "takedata" in the blue tui window.
The bcpm will use whatever mode it was in in the last monitor scan.
Answer the questions as prompted. Note that RA, Dec and name do not have to be 100% accurate as they are just for header information -- as long as you can reconstruct what source you were looking at, "16:20:00 -26:00:00" is just fine.
Choose writing to tape in both cases.
Set the file length to something sensible (e.g., 60 seconds for cal scans, 300 seconds for data scans).
Answer Y to "Ready to roll" when you are in fact ready to roll, and the BCPM will go on taking data until told to stop. Note that this means you will have to stop the cal scans yourself after about a minute or so, though more cal data doesn't hurt.
To stop and keep all sampled data, type "stop" in the blue tui window. To stop and lose whatever data has not yet been written out (not recommended unless you've screwed up!), type "abort" in the blue tui window.
After the scan finishes, wait for the BCPM to say "Idle" before proceeding to the next scan.

After observing:

Quit the BCPM gui.

Miscellaneous

Table of Sample Times in Microseconds

Channel BW (MHz)	x1	x2	x4	x8
1.74	21	42	84	168
1.4	25	50	100	200
1.0	36	72	144
0.7	50	100	200
0.5	72	144
0.35	72	144
0.25	72	144

NB not all modes work!! Those in boldface have been known to work (at least with summed polarizations) at some point in the past. Those in red italics are known not to work.

Troubleshooting

BCPM does not go through the "init" sequence when its Manager is turned on in Astrid/Device Explorer. BCPM and Astrid are still not fully compatible, so this is mostly DevExplorer legacy information. One thing to be aware of is that the BCPM gui must first be running in order for the manager to be happy. Try turning the manager off, starting the BCPM gui, and then turning the manager on again in the DevExplorer Manager menu. If this doesn't work, the manager is probably dead. Try the following recipe:
- Ssh to vortex as monctrl (get password from Operator)
- "Taskmaster vortex status" (BCPM manager is task 9.)
- "Taskmaster vortex stop 9"
- "Taskmaster vortex status" (Wait till task 9 is stopped, max 1 minute.)
- "Taskmaster vortex start 9"
- "Taskmaster vortex status" (Task 9 should have started again.)
- Turn BCPM manager on (or off, then on) in DevExplorer
If Task 9 doesn't stop or restart, or there are continuing Cleo error messages about the BCPM manager, the problem may be a dead process. Try doing "ps" (as monctrl on vortex) looking for bcpm and killing the process. Then go through the Taskmaster process again. If none of this works, call Mark Clark or Amy Shelton!
Blue "tui" window disappears when monitor is started. Bring up tui again (type "tui" or "ui" on command line), then do "powerdown" followed by "init" in the tui window. This should restor functionality.
Levels are always 0 and setpower does nothing. Make sure you have chosen the correct input with the "setif" command. Remember: 1 for 600/800/Lband, 2 for 340/450/Sband, 3 for 85-3.
BCPM I/O rate is 0 MB/sec and the level monitor display is frozen. The BCPM scan is dead. This type of thing can happen for various reasons:
- The IF Rack was balanced (and levels changed a lot) while the BCPM was running.
- That BW/Tsamp mode simply doesn't work.
- The BCPM has decided it is unhappy and doesn't want to take data any more. Yes, this happens.
Suggestions:
- Kill the scan, balance the IF Rack, and restart the scan. If this is a normally functioning mode, it will probably come back to life.
- If the mode often works but is sometimes flaky (eg, 1.4 MHz BW, 50 usec sampling), try switching to another BW/Tsamp and running a monitor scan, then coming back to the mode you want. Alternatively, try cycling between summing and not summing the polarizations.
- Occasionally a normally functioning mode will simply stop working for a while. The only thing I can suggest under those circumstances is to run in a different mode!
No file named "scratch" is being written to the /home/vraid2/scratch/your_login/bcpm2/ area even though the BCPM has been taking data for more than one file length. Things to check:
- Make sure you have selected "Tape" instead of "Disk" in the GO BCPM panel. If it's "Disk", the BCPM will stop taking data after one file length. Select "Tape" and start again.
- Make sure you edited hardware.conf before starting up the BCPM gui. Otherwise, it will be writing to the area that was previously indicated. Check the other person's directory!
- Make sure you did not create a subdirectory named "scratch". If you did, remove it and everything should eventually be all right.
The levels drift very low or very high soon after the start of your scan. Your source is probably rising or setting, so the spillover is changing. Attenuators need to be changed somewhere. The IF rack is probably the best place; don't hit "Balance" but instead add or subtract dBs manually.

Ingrid Stairs

Last modified: Mon Jul 31 16:32:30 PDT 2006