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Summary: A technically orientated instructional film featuring the Rebecca Mark IV device, an airborne transceiver used with Eureka, a ground based transponder for aircraft navigation purposes.
Description: The Rebecca Mark IV was extensively developed during and after the war for use by the airborne forces, supply drops to partisans, the location of ditched aircraft crew, the indentification of adjacent aircraft, blind bombing, to facilitate aerodrome control and as a blind landing aid. The device is demonstrated in this film onboard an Avro Lincoln (serial number RE250). The signal transmitted by Rebecca interrogates the Eureka unit which responds by returning the signal on a different frequency. Rebecca receives this signal by two directional yagi antennas (port and starboard) and is viewed on a cathode ray tube (CRT) display providing the pilot with distance and azimuth information relative to Eureka. The CRT display also provides a graphical presentation of dots to port and dashes to starboard relative to the flight line to guide the pilot of the aircraft. The aircraft’s location could be determined if two or more Eureka beacons were available (triangulation).
The commentary recalls over footage of the device how the prototype Rebecca Mark I was built in 1941 by the Telecommunications Research Establishment, and the Mark IV operating in the 170 to 240 MHz band was an early post war development. It replaced all previous versions and with a total weight of 45 lbs comprised four main units: detachable receiving and transmitting aerials, transmitter & receiver units, control unit, and indicator unit. A remote control facility was available and was fitted to all Royal Air Force and Naval aircraft. The film then illustrates each unit in turn and gives basic operator instructions, aided by animated schematic block diagrams, interspersed with film shots of how the units are connected together, and the progress of the signals to the CRT display.