United States National Radio Quiet Zone

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The United States National Radio Quiet Zone is a large area of land surrounding the National Radio Astronomy Observatory (NRAO) near Green Bank, West Virginia. It is a rectangle of land approximately 13,000 square miles in size and straddles the border of Virginia and West Virginia; it was picked because it has a unique topography that screens out most incoming radio signals, allowing the Green Bank telescopes to receive signals that are otherwise too quiet to be heard over the normal radio background.

This was established by the Federal Communications Commission in 1958 to protect the facilities' radio telescopes from harmful interference. Omnidirectional and high-power transmissions are frowned upon, and fixed radio links are often built as tight-beam directional links in order to avoid overloading the signal amplifiers in the telescope systems.

The National Radio Quiet Zone also protects the antennas and receivers of the US Navy Security Group Activity based at Sugar Grove, West Virginia. NSGA Sugar Grove has long been the home of electronic intelligence gathering systems, and is today said to be a key station in the ECHELON system operation by the NSA.

Not all radio transmissions are prohibited, but station owners must typically coordinate their operations with representatives of the NRAO. Most radio transmitters within the area are licensed, and exceptions are usually determined on a case-by-case basis, with preference given to public safety concerns.