A Sample Feature From Aviation News

King of the Collectors by Dr Alfred Price

In the early 1960s the US Army began using aircraft to intercept enemy radio transmissions and locate enemy transmitters in South Vietnam. At the end of the decade the 224th Aviation Battalion (Radio Research), the unit involved with this work, operated a fleet of nearly 100 aircraft.

Packed with electronics, the latest RC-12Q retains an aerial array connected with the Guardrail Common Sensor and incorporates a large dorsal fairing for the satellite relay equipment. This enables data to be sent to and from ground stations anywhere in the world. (Photo, via author).

In the early 1960s the US Army began using aircraft to intercept enemy radio transmissions and locate enemy transmitters in South Vietnam. At the end of the decade the 224th Aviation Battalion (Radio Research), the unit involved with this work, operated a fleet of nearly 100 aircraft.

De Havilland Canada RU-6A Beaver of the US Army’s 224th Aviation Battalion (Radio Research) in Vietnam. These aircraft located enemy wireless transmitters in the south of the country, by homing on their signals. Note the long vertical receiving aerial mounted on the leading edge of each outer wing. (Photo, via author).

The separate emitter location task was carried out by single-engined de Havilland RU-6A Beaver and twin-engined Beech RU-8D Seminole aircraft. Their rudimentary direction finding systems made location a labour intensive process. If the radio operator in the rear cabin picked up an enemy HF [Morse] signal, he directed the pilot to turn until the aircraft’s wing mounted vertical dipole aerials gave a null signal indicating that the ’plane was flying directly towards or directly away from the transmitter. The co-pilot noted the bearing; the ’plane then made a 90° turn and flew for one minute, then the co-pilot took a second bearing on the transmitter. If the cut of the bearings was narrow, it meant the transmitter was some distance away. If it was wide, it meant the transmitter was nearby. If they appeared to diverge, if meant that on the first bearing the aircraft had been flying away from the transmitter. The ’plane then homed on the signals until the radio operator got a null signal on his non-directional aerial, which indicated that the aircraft was over the transmitter. The pilot then turned the ’plane on its wing, the co-pilot looked down and marked the location on the map.

Guardrail’s ground-based Integrated Processing Facility uses commercial installations linked via fibre-optic network.

This method of location took several minutes and required the aircraft to fly directly over the enemy transmitter, which was feasible only in areas where no enemy air defences were present. Moreover, the process required a continuous enemy transmission lasting between three and five minutes. In practise that required a rather incompetent enemy radio operator, and those did not survive long.

. . . For the full article see the November issue.