Antenna farm

Lore & Background

The history of the term "antenna farm" is uncertain, but it dates to at least the 1950s. For AM broadcasting stations, multiple mast radiators may all be part of a single station's antenna system, while for VHF and UHF the site may be under joint management. A single tower with many separate antennas is often called a "candelabra tower".

Commercial antenna farms are managed by radio stations, television stations, satellite teleports, or military organizations and are mostly very secure facilities with access limited to broadcast engineers, RF engineers, or maintenance technicians. This is for physical security and safety, as there may be a radiation hazard unless stations are powered-down. Where terrain and road access allows, mountaintop sites are attractive for non-AM broadcast stations because they increase height above average terrain, allowing greater reach by avoiding obstructions and increasing the radio horizon. Satellite antenna farms are usually located at remote locations, far from urban development, high-rise buildings, and airplane flight paths.

In the United States, most metropolitan areas have at least one antenna farm. Some cities instead combine many stations onto one tower, often through diplexers into just one or two antennas, such as atop the Empire State Building in New York or the Sutro Tower of San Francisco. Probably the most famous broadcast antenna farm was the World Trade Center Tower One, on which many New York City television and several FM stations had their antennas; all were lost when the Twin Towers collapsed after the September 11 attacks in 2001.

Reader's Guide

Antenna farms have been a significant feature of broadcast and telecommunications infrastructure, enabling multiple stations to share a common location for efficiency and coverage. The practice of co-locating antennas on mountaintops or tall towers maximizes signal reach by improving line of sight and height above average terrain. This arrangement also allows stations to have backup facilities co-located on each other's towers for redundancy.

Antenna farms have often been the source of complaints from local neighborhoods, particularly when a new tower is added. This has been increasingly so for TV stations pursuing construction of new digital television antennas. Because many existing towers are already full or were built before the expectation of DTV, stations have faced the expense of constructing new towers. One such situation occurred in Colorado in the late 1990s and early to mid-2000s, where Denver TV stations needed extra space on Lookout Mountain. Residents and the city of Golden filed legal objections, including challenging the FCC's authority to override local zoning permits. Despite alternatives, a new "supertower" was forced on Lookout Mountain by the U.S. Congress, and the site began operating in spring 2008.

The requirements for an antenna farm include clear line of sight (especially for microwave dishes), freedom from radio interference such as marine radar, higher ground elevation to maximize coverage, distance from high-rise structures and other obstructions, and a minimum distance of 20 miles from airports. Staff typically include RF engineers, broadcast engineers, air conditioning engineers, electrical engineers, maintenance technicians, telecommunications facility managers, and security guards.

Did You Know?

• The term 'antenna farm' dates to at least the 1950s, though its exact origin is uncertain.
• Any area with more than three antennas can be referred to as an antenna farm in telecom circles.
• The World Trade Center Tower One was a famous broadcast antenna farm; its antennas were lost when the towers collapsed on September 11, 2001.
• Antenna farms must be at least 20 miles away from airports to avoid disruption.