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The United States National Radio Quiet Zone is a large area of land centered between the National Radio Astronomy Observatory at Green Bank, West Virginia and the Sugar Grove Research Facility at Sugar Grove, West Virginia. The Radio Quiet Zone is a rectangle of land approximately 13,000 square miles (34,000 km2) in size that straddles the border area of Virginia and West Virginia. It includes all land with latitudes between 37° 30′ 0.4″ N and 39° 15′ 0.4″ N and longitudes between 78° 29′ 59.0″ W and 80° 29′ 59.2″ W.
The National Radio Quiet Zone protects the telescopes of the NRAO facility and the antennas and receivers of the U.S. Navy Information Operations Command (NIOC) at Sugar Grove, West Virginia. The NIOC at Sugar Grove has long been the location of electronic intelligence-gathering systems, and is today said to be a key station in the ECHELON system operated by the National Security Agency (NSA).
The Quiet Zone was created by the Federal Communications Commission (FCC) in 1958 to protect the radio telescopes at Green Bank and Sugar Grove from harmful interference. Restrictions on transmission are tightest within ten miles of these sites, where most omnidirectional and high-power transmissions are prohibited.
Not all radio transmissions are prohibited in the Radio Quiet Zone. For example Citizen's Band radios, police and ambulance radios, and fire department radios are used there. However, large transmitter owners must typically coordinate their operations with representatives of the NRAO, which oversees the NRQZ in agreement with the Sugar Grove facility. The only broadcast radio stations in the inner core of the Quiet Zone are part of the Allegheny Mountain Radio network—with just one station in the AM band, and several low-power FM stations. Exceptions to the Radio Quiet Zone restrictions are usually determined on a case-by-case basis, with preference given to public safety concerns, such as remote alarm systems, repeaters for first responders, and NOAA Weather Radio. Due to the restrictions, the area has attracted people who believe they suffer from electromagnetic hypersensitivity.
Most broadcast transmitters in the Quiet Zone are forced to operate at reduced power and use highly directional antennas. This makes cable and satellite all but essential for acceptable television in much of the region.
Chapter 37A of the West Virginia Code strictly regulates radio transmitters within 10 miles of the Green Bank NRAO facility. Staff of the NRAO routinely patrol radio transmissions within a 20-mile radius of the Green Bank Telescope.