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American airborne radar detector type RT34/ASP-13, 1939-45. The equipment used a directional aerial in the rear fin for both transmission and reception, the main lobe of transmission being such that there was half field strength at plus or minus 45 degrees vertically and 30 degrees horizontally. This cone of coverage was tilted slightly upwards, to provide warning of aircraft diving from steep angles. When an aircraft came within this cone of coverage, pulses sent out from the transmitter were received back in the receiver section of the equipment, and used to operate two warning devices, a red lamp and a bell, situated in the pilot's cockpit. The complete equipment consisted of a transmitter-receiver unit, control box, aerial assembly, associated cabling, and the two warning indicators. The only units which need be accessible during flight are the two warning devices and the control unit, the transmitter-receiver adjustments being pre-set before flight. Leading particulars were as follows :—Frequency: 415 Mc /s. Range: 200 to 800 yards (limited by gate) Power supply: 27 .5volts (25-284), 3.5amps. Receiver IF: 30 Mc /s. Transmitter prf: 300-450 p.p.s Pulse width: 0.4 microsecond Peak pulse power: 200 watts Aerial system: Comprises a folded dipole with one director and one reflector Altitude limits: 2,600 feet. to 50,000 feet approx. Angular coverage: -I- or — 45 degrees vertical + or 30 degrees horizontal (for half field strength)

American airborne radar detector, type RT34/APS-13

Radio Communication

1939-1945

GL Mk.1 radar transmitter. When used in its operational role, the console was housed in a small rotational cabin, mounted on a turntable, or a mobile chassis, with the aerial system above on a framework which could be raised or lowered and dismantled for travelling. Power supplies, telephones, and input / output information lines were fed into the cabin via a system of slip-rings and the cabin rotated by a traversing control column. Synchros carried high-speed and low-speed range and bearing data to a predictor which, after processing the information, inserting various corrections, and calculating a fuze setting, produced polar co-ordinates for laying a battery of guns. The GL Mk.1 transmitter was designed to radiate a pulse of 1.5-3 microseconds duration at a recurrence frequency of 800-2000Hz, the radio frequency being 55-85MHz and the pulse having a peak power of the order of 50kW. The timing of the pulses was controlled by the modulator unit which was situated, with a spare, in the upper left-hand compartment. In this unit, a variable-frequency blocking oscillator and associated shaping circuits generated pulses which, after amplification, passed to the radio-frequency oscillators as positive pulses super-imposed on the steady negative 100-volt grid bias. The grid bias of the oscillator valves was thus reduced nearly to zero for a few microseconds every time the pulse was generated. The oscillator valves were a pair of VT58 valves connected in a push-pull tuned-grid tuned-anode circuit in which lecher lines were employed instead of lumped inductance and capacitance. A low impedance line connected the cathode circuit of the oscillators to the grids of the neutralised triode amplifiers, the anode circuit of which was also tuned by the lecher lines and tapped to feed the aerial. A bank of lamps was provided to simulate the aerial load for tunning purposes and the power output was measured by comparing the brightness with that of a standard lamp supplied from the mains through a variable resistance calibrated in watts. A cathode ray monitor was fitted at the left-hand side in order to check the pulse shape and facilitate tuning. It was fed from tapping points on the high frequency (hf) choke in the aerial coupling system while the time-base deflection voltage was derived from the modulator unit.

GL Mk.1 radar transmitter, 1939

Radio Communication

1939