United States national radio quiet zone
The National Radio Quiet Zone (NRQZ) is a large area of land in the United States designated as a radio quiet zone, in which radio transmissions are heavily restricted by law to facilitate scientific research and military intelligence, a radio quiet zone. It is located in the states of West Virginia, Virginia, and a small part of Maryland.
The Quiet Zone is an approximate rectangle of land, 107.0 miles (172.2 km) on the north edge, 109.6 miles (176.4 km) on the south edge and 120.9 miles (194.6 km) on the east and west edges, comprising approximately 13,000 square miles (34,000 km2). It straddles the borders of Virginia and West Virginia, and also includes a sliver of Maryland. The NRQZ is centered between the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia, and Sugar Grove Station in Sugar Grove, 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.
Most broadcast transmitters in the core of 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. Restrictions on transmissions are tightest within ten miles of the NRAO and Sugar Grove facilities, where most omnidirectional and high-power transmissions are prohibited.
Not all radio transmissions are prohibited in the core of the Radio Quiet Zone. For example, emergency service (police, fire, and ambulance) radios and Citizen's Band radio are permitted. However, large transmitter owners must typically coordinate their operations with the NRAO. The only broadcast radio stations are part of the Allegheny Mountain Radio network—with just one station in the AM band, and several low-power FM stations. Exceptions to restrictions are usually determined on a case-by-case basis, with preference given to public safety concerns, such as remote alarm systems, repeaters for emergency services, and NOAA Weather Radio.
...
Wikipedia