GB500588A - Improvements in or relating to radio apparatus for detecting aircraft - Google Patents

Abstract

500,588. Indicating proximity of aircraft. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., and PLAISTOWE, D. L. Aug. 13, 1937, No. 22355. [Class 37] [Also in Group XL] In a radio system for detecting aircraft comprising a television indicator, a short-wave transmitter and a plurality of short-wave receivers distributed over the detection area and connected to the television indicator by transmission lines, the transmitted waves are modulated with impulses of a frequency corelated with the scanning line frequency of the indicator, and the signals from one or more of the receivers are applied as picture signals to the television indicator. The deflection plates 4, 5 of the cathode-ray tube 1 are supplied with a frame frequency of 50 cycles and a line frequency of 10,000 cycles from the time-base circuits 7, 8 which may be driven from the master source 6.- The output from the line - time-base circuit 8 is fed to the network 9 designed to produce short rectilinear synchronising pulses of, line frequency which modulate a short wave transmitter 11 in the modulator 10 such that the modulation impulses are of longer time length than the synchronising impulses. Radiation from the transmitting aerial 12 is picked up by the distributed receivers 13-16 and applied to the control grid of the cathode-ray tube 1 through transmission lines 17-20, switches 22-25, and the mixer stage 21. In the absence of any reflector in the vicinity of the receivers a black bar is seen down one edge of the television " raster " (assuming the framing direction to be vertical) due to the elongated pulses transmitted. If an aircraft is near one of the receivers, that receiver picks up an indirect wave reflected from the aircraft which is out of phase with respect to the direct wave and an additional black bar, which moves with the aircraft, is seen on the " raster." By opening all the switches 22-25 and closing them one at a time the direction of the aircraft can be determined.