A radio quiet zone is an area where radio transmissions are restricted in order to protect a radio telescope[1] or a communications station[2] from radio frequency interference. The Radio Regulations of the International Telecommunication Union (ITU) define interference as being detrimental to radio astronomy if it increases measurement uncertainty by 10%. In particular, the applicable regulation is known as ITU-R Recommendation RA.769, "Protection criteria used for radio astronomical measurements".[3] Equipment that can cause interference includes mobile phones, television transmitters, and CB radios, as well as other electrical equipment.[1]
Quiet zones are located in areas that are sparsely populated, and may be enforced by government legislation.[1] A radio quiet zone is often divided into two zones: an exclusion zone where all radio emissions are prohibited, and a larger coordination zone of up to 100 km2 where the power levels of radio transmissions are suitably limited so as not to interfere with the radio telescope.[3]
Formal radio quiet zones exist around many observatories,[4] including the Murchison Radio-astronomy Observatory in Australia,[1] the National Radio Astronomy Observatory and the Sugar Grove Station in West Virginia, United States (the United States National Radio Quiet Zone),[2] the Itapetinga Radio Observatory in Brazil,[5] and MeerKAT in South Africa as examples.
The ITU has recommended designating two locations in outer space as radio quiet zones: the shielded zone on the Moon's far side, and the Sun-Earth Lagrangian point L2.[6]