GBT OPERATIONS PROCEDURES

 Number: OP-08
Title: VLBI procedures Last Revision: 9 Aug 02

General

The following procedures are used to prepare for and complete VLBI observations using the GBT. 

Info 

This procedure consists of tasks to be completed before, during, and after VLBI observing. Use the following guide to determine when tasks should be completed:

The character " ^ " is used below to emphasize spaces between dialog elements.

Observing Preparations

Tapes

    Receiving Tapes

STEP

 ACTION
1 Acquire tapes at least a week before scheduled observing. Contact the VLBA tape librarian at Socorro (vlbatape@aoc.nrao.edu) to request tapes. Proceed to step 2 when tapes arrive.
2 Update web based tracking program:
  • From any web browser go to: http://magnolio.nrao.edu/track/ (login: gbvlba) (track)
  • On the page "Tape Tracking Home Page for GB - Shipping and Receiving", press the Receive a Shipment button.
  • Follow instructions provided on additional pages.
 

 

    Prepassing Tapes

STEP

 ACTION
1 Check recorder power is ON.
2 Clean the tape path and recorder heads with alcohol using wipes and/or Q-tips.
3 Mount and thread tape.
4 Open an xterm window and slogin to vortex as follows:  slogin ^ vortex ^ -l ^ gbvlbi  (vlibN140)
5 Bring up the RSCREEN package:  rs  (RSCREEN window will appear)
6 In RSCREEN window, select the Prepass option (TAPE » PREPASS)
  • Tape will spool to the end (takes about 10 minutes).
  • Carefully unthread tape from heads and tape path.
  • Clean the tape path and recorder heads.
  • Rethread tape and continue PREPASS menu (tape will rewind). 
  • After the tape has re-wound, continue to "Testing Tapes for Flange Forcing". 
    Testing Tapes for Flange Forcing

STEP

 ACTION
1 Complete steps for prepassing the tape. Leave the tape on the drive.
2 Rotate the tape reel on the drives so the GREEN serial number label is at the top. 
3 Place the one inch aluminum block between the flanges so that it rests on the tape.
4 Using the blue 5mil shim, try to slide it between the aluminum block and the flange.
  • If the shim does not or just barely slides between the flange and block, it passed the test.
  • If the shim easily slides between the flange and block, it failed the test. Prepass the tape again and retest for flange forcing.  Repeated failures or other problems indicate a bad tape. Reject it and send it back to Socorro.
5 Remove tape from drive. Mark as prepassed and tested accordingly.

Schedules  

    Downloading Schedule Files

STEP

 ACTION
1 Determine the project name from current GBT schedules. Note for later use.
2 To download schedules from Socorro:
  • Go to web page: www.aoc.nrao.edu/vlba/html/vlbahome/observer.html and select Aspen.
  • In the directory, click on the desired month/year.
  • In the next directory, click on the project name.
  • Downloaded and save the xxxcrd.gb and xxxsch.gb files to the ~gbvlbi/obs directory.
  • Print the schedules. Skip to step 5.
3 To download schedules from NASA:
  • Open an xterm window and login to sadira as shown:  ssh ^ sadira ^ -l ^ gbvlbi  (vlibN140)
  • Change to the "obs" directory:  cd ^ obs
  • Enter:  ftp ^ cddisa.gsfc.nasa.gov
  • At the login enter:  vlbigeo  (@100uasXY)
  • Change directory: cd ^ mmmyy/ (mmm=month, yy=last digits current year)
  • Enter:  get ^ xxx.skd (replace xxx with project name)
  • quit  (follow with Y)
4 Print the schedule files, enter:  a2ps ^ *.gb
5 Review the schedule. Items to note to prepare for VLBI observing include:
  • Start/stop times and dates.
  • Tapes needed and when changes will be required.
  • Receiver, band, center frequency, baseband converters needed, etc.
  • Note the xxxcrd.gb file name for later use in converting this file. (xxx is the project name part of file name).
 
    Converting Schedule File to a GO Table

STEP

 ACTION
1 Open an xterm window and slogin to vortex as follows:  slogin ^ vortex ^ -l ^ gbvlbi  (vlibN140)
2 Change to the "obs" directory:  cd ^ obs
3 Using VI, Pico, XJed, or other editor open the OBSERV.TX file and duplicate the last line. 
  • Modify the line by changing the xxxcrd.gb file name to the current one shown on the schedule (file names must not be greater than 8 characters).
  • Change the start time to the current time.
  • Change the stop time to a few minutes after the scheduled stop time.
  • Save and exit from the editor.
4 Convert the schedule file to a GO table:  vlba2go ^ -f ^ xxxcrd.gb (replace xxx with project name) (creates a table ".obs" file).
5 Copy the file created to the ~gbtops/vlbi directory:  cp ^ xxx.obs ^ ~gbtops/vlbi (replace xxx with project name)
6 Print a copy of the file for reference during observing:  print ^ xxx.obs
7 Exit vortex.

System Pre-Checks

    DAR & Recorder

STEP

 ACTION
1 Check DAR and Recorder power are ON. If not, turn power on and complete step 2.
2
  • Slogin to vortex as follows:  slogin ^ vortex ^ -l ^ gbvlbi  (vlibN140)
  • Launch RSCREENS window, enter:  rs
  • Go to the setall screen (MCB » SETALL). Selecting this option sets all interface address blocks.
  • Go to the send screen (PARM » RECPARM » SEND). Selecting this options reads/sets tape recorder parameters.
    Site Time

STEP

 ACTION
1 Compare the IRIG (site time) module (located under 20meter OCT in OVLBI) to GPS (on cart in OVLBI). Both should be on the same second. Also check that year, month, and day is correct. 
2 From Cleo launch the Site Time application.
  • Check that Site1hz to TAC is less than a few 1000 ns. If not, call John Ford or Frank Ghigo.
  • Check that Site1hz to GBT_VLBA (VLBI Formatter) is less than a few 1000 ns. If not, push the reset button on the DAR's Station Time module. Recheck values.
  • Compare Cleo UTC time with IRIG (site time display module in electronics equipment room). Both should be on the same second.
3 Check/set the VLBA Station Clock. 
  • Launch an RSCREENS window (see DAR & Recorder, step 2).
  • Go to the clock screen (OBS » CLOCK). Check the year, day, hour, minute, and second (they should agree exactly with the IRIG and GPS). Use the CLOCK screen options to adjust the VLBA Station Clock if necessary.
4 Compare site time with US Naval Observatory master clock. Phone: 1-200-762-1401/1069
    NetVLB Demons

STEP

 ACTION
1 Confirm on-line demons are running:
  • In an xterm window log in to vortex:  ssh vortex
  • Enter:  ps ^ -ef ^ | ^ grep ^ netvlb (if running, a time stamp and netvlb should be displayed)
NOTE TaskMaster can also be used to confirm the netvlb demon is running.

Setting Up to Observe

    System Setup & Monitoring Screens

STEP

 ACTION
1 Launch the following Cleo devices if not already up:
  • Antenna
  • LO1
  • IF Rack
  • Converter Rack
  • Switch Signal Selector
  • Receiver (check schedule for which one)
  • Scan Coordinator
2 Run the observing setup script:  
  • Open an xterm window and change to the vlbi directory:  cd ^ vlbi
  • Run script:  glish ^ -l ^ xxx.g (replace xxx with script name for this run).
  • Exit the window once the setup is complete.
3 Confirm antenna and electronic devices are set properly for this observing run (see available setup instructions).
4 Reboot the VLBA station computer (vlbagb; near tape recorder). In the Vxworks window enter:  reboot
5 At Ops console, start the RSCREENS window unless already up.
6 At Ops console, start the GBT VLBI Link window. In a new xterm window enter:  slogin ^ vortex ^ -l ^ gbvlbi  (vlibN140) then enter: GV (launches the GBT VLBI Link window). This window must be kept running during observing.
7 In RSCREENS, go to the clock screen (OBS » CLOCK). Reconfirm correct year, day, hour, minute, and second (they should agree exactly with the IRIG and GPS). Use the CLOCK screen options to adjust the VLBA Station Clock if necessary.
    Recording System

STEP

 ACTION
1 Check DAR power supplies (near top of rack). Voltages nominal (5v and 15v).
2 Check timing module indicator lights:  Xmt Actv (Green light on);  Msg Actv (Green light on).
3 Clean the tape path and recorder heads with alcohol using wipes and/or Q-tips.
4 Get a tape. Fill in the label with project code and current date/time. Place a red dot on the label.
5 Mount and thread the tape.
6 From an RSCREENS window, Go to the MOUNT menu (TAPE » MOUNT) and execute the MOUNT option (recorder will read label number then move to position).
NOTE If using Recorder 2, you will have to manually enter the tape's serial number and confirm it in the DAS menu.

Running the Observation

STEP

 ACTION
NOTE All steps must be completed with antenna on source before the scheduled start time of the first source.
1 Ensure all required antenna drives are activated and ready.
2 Initiate GBT Observe unless already up, enter:  GO  (GO will proceed to launch)
  • On the GO main screen: Enter the project and PI name. Select Continuum mode, Track procedure, and enter center frequency value.
  • Bring up the Tables screen and load the scheduled observing file (normally in the ~gbtops/vlbi/ directory). Select all lines in the file.
3 Press the RUN button to begin slewing to/tracking the first source.
4 Check/set IF levels:
  • Go to the IF Rack and balance the IFs.
  • Go to the RSCREENS window and bring up two IF screens: (MODULE » IFDIST).  Set one as IF1, the other as IF2.  Note on schedule which channels will be used (usually either A/C, or B/D).
  • VLBA IF power levels ( range between 10,000-20,000). Adjust via the Converter Rack (attenuators) if necessary. 

Note: IFDIST channels connect to the GBT converter rack as follows:

  • IFDIST 1 channel 1 is VLBA_DAR:A (usually RCP, from Converter Rack A)
  • IFDIST 1 channel 2 is VLBA_DAR:B (usually RCP, from Converter Rack B)
  • IFDIST 2 channel 1 is VLBA_DAR:C (usually LCP, from Converter Rack A)
  • IFDIST 2 channel 2 is VLBA_DAR:D (usually LCP, from Converter Rack B)
  • Rack A, converter modules 1 and 5 support 600- 800 MHz, L-band, and Ku band.
  • Rack B, converter modules 9 and 13, support S and X-band receivers.
NOTE Observing/recording will begin automatically based on the observing schedule
5 Periodically during observing:

Ensure antenna is on source per schedule.

Use RSCREENS to:

  • View Data Acquisition Summary information (OBS » DAS)
  • Check for formatter errors (FORMAT » FORMATTER)
  • Check for problem messages (OBS » CHECKALL)
  • Check for flagged errors (OBS » FLAG)

Use the VLBI GBT Link window to:

  • Monitor GBT-VLBA Status information.
  • Ensure tape is spinning when required and footage is correct (compare to schedule).
  • Monitor weather data being recorded.
6 As needed during observing:

Update observing log to reflect:

  • Unusual weather (snow, heavy rain, high winds). Other parameters are automatically logged.
  • Interruptions to observing.
  • Problems.
  • Other comments deemed necessary by the operator. 

Change tape reels when/if required (see step 7).

7 To change tapes:
  • If tape didn't automatically unload, in RSCREENS go to the MOTION window (TAPE » MOTION) to unload it. Follow screen prompts and remove reel when done.
  • To load a new tape, clean the recorder heads then mount/thread the new tape. Go to the MOUNT menu (TAPE » MOUNT) and execute the MOUNT option (recorder will read bar code then move to position). If possible, label and attach red dot before mounting. 

Post Observation Tasks

Sending Tape Reels to Socorro

STEP

 ACTION
1 Ensure tapes have a red dot on their labels and that the labels include:
  • Site (GB)
  • Project code
  • Recorder number
  • Time mounted
  • Time un-mounted
2 Deliver tape(s) to Mailroom:
  • Check tape serial number is on bar code label on outside of shipping case.
  • Drop tapes off in the mail room and advise the receptionist. They will provide you FedEx airbill numbers.
3 Update web based tracking program:
  • From any web browser go to: http://magnolia.nra.edu/track . (gbvlba/track)
  • On the "Tape Tracking Home Page for GB" page, enter Socorro in the or Correlator box. Press the Make a Shipment button.
  • On the "Make a Shipment from GB" page ensure the destination box shows SOC and the shipper is FEDEX. In the dialog box enter the airbill (Waybill) number, project, and tape numbers according to instructions on the page. An example entry is shown below. Press the Submit Shipment button when ready.

  • On the "Shipment Summary for GB" page, review your entries for accuracy. Use the browsers Back button should corrections be needed. Press the Record Shipment button when ready. 
  • The web based tracking program is now updated.

Note: Additional information is provided on the web page.

Sending Data Log Files to Socorro

STEP

 ACTION
1 Open an xterm window and slogin to arcturus:  slogin ^ arcturus ^ -l ^ gbvlbi  (vlibN140)
2 Change to the GB data directory:  cd ^ mdata/GB
3 Copy the files:  scp ^ xxx.dat ^ vlbaops@jansky:/export/home/jansky/mdata/GB (substitute xxx.dat with correct filename).
4 Exit arcturus.

Sending Ops Log Comments to Socorro

STEP

 ACTION
1 Prepare an E-mail containing operations log comments and tape numbers.
2 Send the message to the following NRAO addressees:  vlbaops, jromney, cwalker, jwurnig, cbignell, and fghigo. 

Prepared by: Dave Rose

Last modified on 9Aug02