AN/TRC-97

Lore & Background

The AN/TRC-97 project was initiated in 1962 as an ultra high frequency tropospheric scatter communication system to support the Marine Tactical Data System. A preproduction model was delivered to Marine Corps Base Quantico in late 1964 and underwent testing and evaluation until June 1967. In service, it provided data, voice, and text communications between Tactical Air Operations Centers, Tactical Air Command Centers, and MIM-23 Hawk missile batteries. During the Vietnam War, communist forces targeted the system's antennas, but marines found they could substitute them with 5-gallon coffee cans and still communicate over 50 miles.

The system could be connected to one of three mobile antennas: the MRT-2 parabolic tropospheric antenna (15 feet across, covering up to 160 km), a feed horn type mounted on a 30-foot pole, or a set of 8-foot parabolic dishes on 15-foot poles. Antennas were transported on trailers and manually erected. The system was powered by a 3-cylinder diesel or later a turbine generator.

A typical crew consisted of two or three wideband technicians and one power production technician. Two units could be used back to back for relay capability at the baseband level. The system could be remotely monitored from up to 2 miles away using the BZ109 test and monitor set.

Three propagation modes were available: tropospheric scatter, obstacle gain diffraction, and line-of-sight. Tropospheric scatter and obstacle gain diffraction typically used the 1 kW klystron, while line-of-sight used the 1W traveling wave tube, later replaced by a solid-state 1W amplifier.

The receiver could pick up signals as low as -105 dBm; the modified TRC-97A could receive signals as low as -102 dBm. It used tunnel diodes to amplify low signals. The radio set was housed in a van approximately 5 feet and loaded onto an M1028 pickup truck, with a trailer hauling antennas and generator.

Reader's Guide

The AN/TRC-97 was initially developed for the Marine Corps and later adopted by the Air Force, which added an additional 12 multiplex channels in a module called the baby mux, creating the TRC-97A. The Air Force used the system for 20 years into the 1980s. It was employed by several units, including the 601st Tactical Control Wing in Germany, the 606th Tactical Control Squadron in Basdahl, Germany, and the 602nd Tactical Control Squadron in Turkheim, Germany, which closed in 1985. The 728th Tactical Control Squadron at Duke Field, Florida, also used it.

In the 1970s, several TRC-97s were turned over to Air National Guard bases. The 5th Tactical Control Group at Clark Air Force Base in the Philippines used the system extensively for communication links between radar sites and aircraft bases during the Vietnam War. The 5th Combat Communications Group at Robins AFB, Georgia, was also a major user. The TRC-97 was superseded by the more modern, less maintenance-intensive digital AN/TRC-170.

Did You Know?

• Its receiver used tunnel diodes, which rely on quantum mechanics theory, to amplify very faint signals.