Largest radio quiet zone

The largest radio quiet zone is the Karoo Central Astronomy Advantage Area, which covers an area of around 106,306 km2 (41,044 square miles) in South Africa. It surrounds the planned location of the South African component of the Square Kilometer Array, a massive radio telescope which will pull together data from massive dish complexes in South Africa and Australia. The Karoo Central Astronomy Advantage Area was established by the Astronomy Geographic Advantage Act, which was passed by the South African parliament on 17 June 2007, and the regulations restricting radio transmissions will come fully into effect in December 2021.

Radio quiet zones are areas where there is a legally enforced ban on commercial radio transmissions. These bans typically restrict the use of radio and television transmitters, ham radio equipment, mobile phones and other devices that can interfere with the operation of radio telescopes or sensitive communications equipment. Most have an inner and outer area, with general restrictions applying to the outer area, while the inner area is covered by an even stricter set of covenants, barring things like domestic wi-fi and microwave ovens. At Karoo, this area is called the Karoo Core Astronomy Advantage Area and covers around 134 km2 (51 square miles).

Beyond the Central area, where active restrictions are applied to radio transmissions, there is a larger "co-ordination area", where activities that might cause problems for the SKA have to be reviewed to assess the risk.

Prior to the creation of the Karoo Central Astronomy Advantage Area, the largest radio quiet zone was the United States National Radio Quiet Zone, which covers an area of around 13,000 square miles (33,670 km^2) in West Virginia and Virginia. This was established in 1958 to protect the Green Bank Observatory.