Interference Protection

Quick Links: NRQZ Applicants; GBT RFI GUI

Radio Frequency Interference Protection

Astronomers measure signals in terms of Janskies – 10-26 Watts/meter2/Hertz, and the GBT often measures signals of milli- or even micro-Janskies. That’s a decimal point with 32 zeros after it:

0.00000000000000000000000000000001 W/m2/Hz !!

This is much less than, say, the energy of a single snowflake landing on the ground.  Another possible way to look at this is that if you were to take your cell phone to Mars, its energy as seen here on earth would be much, much greater than the energies frequently measured by the GBT.  This is why it is incredibly important for the science we do that we are protected by two separate regulations which protect the GBT and the other site instruments from locally produced radio frequency interference.  The Green Bank Interference Protection Group is responsible for minimizing radio frequency interference to astronomical observations from equipment and activities at the Observatory, in the West Virginia Radio Astronomy Zone (WVRAZ), and in the National Radio Quiet Zone (NRQZ).

The National Radio Astronomy Zone

The National Radio Quiet Zone (NRQZ) was established by the Federal Communications Commission (FCC) in Docket No. 11745 (November 19, 1958) and by the Interdepartment Radio Advisory Committee (IRAC) in Document 3867/2 (March 26, 1958) to minimize possible harmful interference to the National Radio Astronomy Observatory (NRAO) in Green Bank, WV and the radio receiving facilities for the United States Navy in Sugar Grove, WV. The NRQZ is bounded by NAD-83 meridians of longitude at 78d 29m 59.0s W and 80d 29m 59.2s W and latitudes of 37d 30m 0.4s N and 39d 15m 0.4s N, and encloses a land area of approximately 13,000 square miles near the state border between Virginia and West Virginia.

Further information on the NRQZ can be found here.

West Virginia Radio Astronomy Zone

The West Virginia Radio Astronomy Zoning Act (§37A-1-2 of the West Virginia Code) makes it illegal operate, or cause to be operated, any electrical equipment which causes harmful interference with the reception of radio waves.   The protection extends at varying levels up to a 10 miles radius from the telescopes on site.

Further information in the WVRAZ, as well as site regulations on RFI, can be found here.

The Site

The Green Bank Observatory site is broken into two protections zones, one for the laboratory, housing, and visitor facilities (Zone 2), and one for the Radio Astronomical Instruments themselves (Zone 1 aka the Radio Astronomy Instrument Zone) , and the interference protection policies for the site are separated according to the zone. More details on the site zoning and regulations can be found here.

RFI Monitoring

While there is currently no RFI monitoring antenna on site, the GBT is used periodically to monitor the sky at different frequencies to look for interference. The monitoring scans are available both online and through a site-based gui. The gui allows for significantly more data to be displayed and uploaded, while the web-based system provides a quick and easy look into the GBT’s RFI environment for everyone.