Tropospheric scatter

(communications) Scatter propagation of radio waves caused by irregularities in the refractive index of air in the troposphere; used for long-distance communications, with the aid of relay facilities, 180-300 miles (300-500 kilometers) apart. Also known as troposcatter.

A term applied to propagation of radio waves caused by irregularities in the refractive index of air. The phenomenon is predominant in the lower atmosphere; little or no scattering of importance occurs above the troposphere. Tropospheric scatter propagation provides very useful communication services but also causes harmful interference. For example, it limits the geographic separation required for frequency assignments to services such as television and frequency-modulation broadcasting, very-high-frequency omnidirectional ranges (VOR), and microwave relays. It is used extensively throughout most of the world for long-distance point-to-point services, particularly where high information capacity and high reliability are required. Typical tropospheric scatter relay facilities are commonly 200–300 mi (320–480 km) apart. Some single hops in excess of 500 mi (800 km) are in regular use. High-capacity circuits carry 200–300 voice circuits simultaneously.

Tropospheric and line of sight communications

Boswell Bay, Alaska White Alice Site, Tropospheric scatter antenna and feeder.

Tropospheric scatter (or troposcatter) is the scattering of distant TV and FM radio stations by the troposphere so that they travel farther than the line of sight. This effect sometimes allows reception of stations up to a hundred miles away.

The phenomenon has been used to build communication links in a number of parts of the world. Large billboard antennas focus a high power radio beam at the troposphere mid-way between the transmitter and receiver. A certain proportion of the signal is refracted and received at a similar antenna at the receiving station.

One such link operated between the North of Scotland, at Mormond Hill and the Shetland Isles.

US Army TRC-170 Tropo Scatter Microwave System

The U.S. Army uses tactical tropospheric scatter systems developed by Raytheon for long haul communications. The systems come in two configurations, the original "heavy tropo", and a newer "light tropo" configuration exist. The systems provide four multiplexed group channels and trunk encryption, and 16 or 32 local analog phone extensions.

The U.S. Marine Corps also uses the same device, albeit an older version.

See also

• Radio propagation
• Microwave
• ACE High - Cold war era NATO European troposcatter network
• White Alice Communications System - Cold war era Alaskan tropospheric communications link
• List of White Alice Communications System sites
• TV-FM DX

External links

• DART-T
• Russian tropospheric relay communication network
• FS-1037C definition of tropospheric scatter
• Troposcatter communication network maps

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