Patent GB-1213630-A (GB)
Title: Improvements in or relating to vehicle monitoring systems
Inventor: PERCIVAL WILLIAM SPENCER
IPC: G01S13/78
Filed: 1966-12-24
Abstract: 1,213,630. Vehicle radar signalling. ELECTRIC & MUSICAL INDUSTRIES Ltd. 22 Dec., 1967 [24 Dec., 1966], No. 57843/66. Heading G4Q. [Also in Division H4] In a land vehicle monitoring system each vehicle carries a radio interrogator/transponder, a vehicle can determine its headway from a transponding vehicle, the interrogator codes its emission in dependence on its path, and a transponder responds selectively to differently coded signals. In the embodiment omnibuses travelling on a special track are restricted to those carrying the interrogator and transponder shown in Fig. 1. A coded pulse train from modulator 3 is transmitted from the interrogator, and if such a signal is received by an aerial 40 from the following omnibus coding circuit 46 affords transmission of a coded signal on a different carrier frequency but only if detector 44 received a correctly coded signal. A signal received by interrogator aerial 11 produces an output from detector 21 only if correctly coded. The output of range unit 19 is compared with the optimum inter-vehicle spacing (i.e. headway) derived from the speed of the omnibus and green, amber and red lights in display 18 are actuated according to whether the actual headway is greater than, near to, or less than, the optimum headway; if the headway continues to decrease when the red light is on, it flashes, and if this is ignored the brakes are applied automatically. Failure detection.-If unit 8 senses lack of   magnetron 4 output, switch 2 changes power to the other modulator 3 and magnetron 4; if the supply 1 fails warning signal 15 is operated. A testing arrangement is provided: a portion of the transmitted signal is leaked from the interrogator to the transponder and vice-versa, the circuit incorporating delay line 17 and gate 24; the delayed test signal from the interrogator causes a reply signal from the "own" transponder, unit 12 comparing the amplified reply signal with the interrogator signal as passed by gate 16 and if the transponder is not functioning satisfactorily the warning signal 15 is actuated. Further failure detection units 29, 30 operate a warning signal 31 if the transmitter or receiver respectively of the transponder fail: signal 31 also causes a transmitter 38 to radiate a signal to cause respective displays 18 of nearby omnibuses to warn of the proximity of a vehicle with a faulty transponder. Coding and traffic arrangements. Fig. 2.-In order to cater for a plurality of traffic lanes, each lane (e.g. main highways ME, MW, sidings SE, SW and lanes PE, PW between stations and public highways) has a separate radar pulse code and a further code is provided for fixed transponders at merge points P 2 , P 3 , P 7 ; the coding is r spaced pulses for the rth. code, the 7-pulse code being for actuating the fixed transponders. The transponders on vehicles operate on the same code as vehicles in the same lane but transmit back to their interrogators only a single pulse following the last code pulse, the interval between the latter and the returned pulse being utilized as a measure of the headway. A track transponder always responds to interrogation by a single pulse after the last code pulse. To warn a vehicle of the necessity to change its radar code when changing lane, and to warn of approach to a merge or diverge point, coded sets of magnets in the tracks are provided: e.g. if approaching diverge point P 1  a blue light is produced in the cab and if proceeding along lane ME a second magnetic code switches off that light, but if the driver wishes to go along siding SE, he biases an appropriate switch so causing the radar code to alternate between those appropriate to ME and SE, and after passing P 1  a magnetic code changes the radar code to SE and switches off the blue light.