The History of Cable Nets in Communications

When we talk about cable nets, we normally think about large span roof structures. However, there is a class of cable net structures that have been largely ignored by the structural engineering community but have provided significant service in the area of research, forecasting, defense communication and public broadcasting. These cable nets provide the primary radiation source for the generation of radio waves over a wide range of broadcast bands. Very low frequency arrays may span over 300 m (980 ft) between towers and may be as tall as 350 m (1150 ft). Some horizontally polarized arrays span between mountain tops that are miles apart. These giant antennas are used to communicate with submarines at very low frequencies. Despite the use of satellite communications in military applications, the VLF antenna is still part of the Navy's communication system. Other cable net antenna arrays broadcast in the shortwave band and have served to provide uncensored news and information to people in countries who otherwise would only hear the "party line". Such broadcast arrays in Europe operated by Radio Liberty and Radio Free Europe played an important role in ending the Cold War. Similar antenna systems are in use today by the US International Broadcasting Bureau and the BBC, and provide worldwide coverage. Many other countries have similar system in their broadcasting system. Shortwave radio broadcasting is still the most efficient and least costly means of reaching a wide audience. Other uses of cable net antenna systems have more clandestine uses. These systems have been used for direction finding and over the horizon radar. Direction finding arrays are typically circular arrays for omni directional interception. Depending on the application, these arrays can have a diameter as large as 350 m (1150 ft) suspended from 40-m (130 ft) towers. Using the ionosphere and special computational techniques, shortwave antenna systems can pin point radio transmissions over 3000 km away. Over-the-horizon radar systems typically use vertically suspended cable net arrays. These systems can detect targets as far as 3500 km away in one "hop". OTH is also being used to monitor ocean-surface winds and current over data-sparse areas that would otherwise require thousands of widely dispersed instruments.