VLBI on the Green Bank 43-meter (140-foot)

The 140-foot telescope at NRAO-Green Bank uses a VLBA-type data acquisition system for VLBI experiments. The old Mark 3 system is no longer available. Note also that Mark 2 recording is no longer available, either.

Click here for general VLBA information.

Similarities with the VLBA

  • The data acquisition system is very similar to those at all the VLBA stations.
  • There are eight double-sideband baseband converters with bandwidths settable between 62.5 KHz and 16 MHz.
  • The recorder can record up to 14 tape passes.
  • All VLBA and some Mark 3 modes are supported.

    • Differences from the VLBA

  • There is only one tape recorder, so users must allow time in the schedule for tape changes (allow 10-15 minutes).
  • Both thin (18000-ft reels) and thick tapes (9000-ft reels) are supported, but thin tapes are preferred.
  • Quick changes of observing band are not possible, because this requires changing a receiver, typically a 2-4 hour process.
  • The 140-ft does not observe all the bands that the VLBA does. Compare the frequency ranges in the table below with the frequency table in the VLBA Observational Status Summary before selecting bands.

    Scheduling

    Scheduling is normally done in cooperation with the VLBA analysts and operators in Socorro. The system needs two files: a VLBA-type schedule file ("*.crd") file, and a pointing file for the 140-ft. These can be produced with the NRAO "sched" program - see the general VLBA documentation for more information. Or one can use PC-SCHED to produce a ".drg" file, and ask the VLBA analysts to generate the necessary files from that. The files should be put on the machine "aspen.aoc.nrao.edu" in the "vlbiobs" account. The Green Bank contact should be notified when files are ready.

    Observing Bands and LO equations.

    Use Fif from the table for the BBC setting. 
    Wavelength     Observing    L.O. equation     Spectrum     IF BW
   (cm)        band (MHz)      MHz             inverted     MHz
---------  --------------  ------------------ ---------    -----
    90       300 to   350  1005 - Fsky  = Fif   Yes          80
    50       560 to   640  1275 - Fsky  = Fif   Yes          80
    22      1300 to  1360  Fsky - 725   = Fif   No           80
    21      1360 to  1430  Fsky - 725   = Fif   No           80
    18      1600 to  1720  2295 - Fsky  = Fif   Yes         270
     6      4956 to  5013  5775 - Fsky  = Fif   Yes         270
     1.3   22050 to 22350  Fsky - 21425 = Fif   No          270

    More information on receiver setups.

    Green Bank Contact people:

  • Frank Ghigo (email: fghigo; 304-456-2208)
  • Rich Lacasse (email: rlacasse)
  • Dana Balser (email: dbalser)

  • Return to 140-ft home page.
  • Return to Green Bank home page.
  • Go to main NRAO home page.

    • fghigo@nrao.edu last changed this page 24 Nov 1997