GB1507050A - Interrogator/transponder systems - Google Patents

Abstract

1507050 Road-traffic signalling-apparatus PLESSEY CO Ltd 21 March 1975 [2 April 1974] 14625/75 Heading G4Q [Also in Division H4] In an interrogator-responder system for vehicle detection and traffic signal control, a signal radiated from an interrogator serial 6 in or by a roadway, traffic lane &c. is used to operate a vehicle borne transponder transmitter 2 which thereafter radiates predetermined coded data signals. The interrogator includes a receiving aerial 7 having operatively associated with it a code recognition unit 13 responsive only to predetermined coded data signals indentifying particular vehicles, this unit being coupled to traffic signal control arrangements, e.g. at 14, 15, 16. The interrogator also includes vehicle detector arrangements 8 responsive to signal changes resultant upon the passage of any vehicle over or by the receiving aerial and arrangements coupled (at 11) to register such passage. The predetermined coded data signals are radiated from the vehicle transponder at a frequency derived from the frequency of the signal radiated from the interrogator aerial. The traffic signal control arrangements may be traffic lights which clear a route for buses, fire engines &c. The coded signals in the described embodiment are phase modulated on to a carrier at half the frequency of the transmitted interrogator signals and are detected by a demodulator 8, which receives the transmitted signal via a frequency divider 9, as reference. The detector responds to slow phase variation to provide an output at 11 indicating vehicle passage, and to rapid variation to provide the actual vehicle code on line 12. In the vehicle transponder (Fig. 2) the received signal is detected by a receiver loop and passes via an interface unit 18 to provide pulses at frequency f each of which actuates a counter 19 (supplied from a battery 40). Pulses at frequencies f/ 2 ,f/ 32 ,f/ 64 ,f/ 128 are taken from the counter and applied to a logic circuit 29 which produces bursts of pulses at frequency f/ 2 in code combinations determined by the other counter outputs. These bursts are transmitted via amplifier 35 and transmitter loop 3. If the vehicle is stationary over an interrogator loop, a reset logic system 41, 42 is activated by the repeated reception of interrogator signals to reset the counter.