The Green Bank Interferometer (GBI)

Black & white photo of the Green Bank Interferometer, looking from the west
The Green Bank Interferometer (GBI) is operated by the National Radio Astronomy Observatory (NRAO) at its Green Bank site in West Virginia. It includes three radio telescopes of 85-foot (26m) diameter, designated 85-1, 85-3, and 85-2 from left to right in the picture at left. (85-1 is also known as the Tatel Telescope.) At present, 85-3 is devoted to continuous monitoring of pulsars; 85-1 and 85-2 form a one-baseline interferometer.

Note: the GBI monitoring program has ceased as of October 6, 2000, due to lack of funding. Anyone interested in using the GBI who may be able to provide operating funds should contact Phil Jewell (

Green Bank 3-element interferometer looking from the west. The 300-ft and 140-ft are at left.


Credits: The Green Bank Interferometer is a facility of the National Science Foundation operated by the National Radio Astronomy Observatory.  From 1978-1996, it was operated in support of USNO and NRL geodetic and astronomy programs; after 1996 in support of NASA High Energy Astrophysics programs.

Technical Data: 2-element interferometer.

  • Baseline: 2400 meters at an azimuth of 62 degrees (E of N).
  • Bands: 8.3 GHz (X-band) and 2.25 GHz (S-band) with 35 MHz bandwidth.
  • Receivers: Cryogenically cooled, dual frequency, dual polarization. Both X and S bands simultaneously observed in both right and left circular polarizations.
  • System temperature: About 35 K in Sband and 45 K in Xband.
  • Sensitivity: RMS noise in a 5-minute scan is about 6 mJy in S-band and 10 mJy in X-band for point sources.
  • Minimum integration time: 30 seconds.
  • Resolution: About 3 arcseconds fringe at X-band and 11 arcseconds at S-band.
Modified on Tuesday, 11-Mar-2003 16:06:09 EST