GB1418325A - Method of distinguishing traffic radio areas - Google Patents

Abstract

1418325 Radio signalling BLAUPUNKT-WERKE GmbH 17 Aug 1973 [19 Aug 1972] 39057/73 Heading H4L A radio transmitter transmits information, e.g. traffic news on a subcarrier of above audiofrequency, which in turn modulates a main carrier, the subcarrier being amplitude modulated with a frequency outside the audio range which is indicative of the transmitter. As described the transmitter is included in a system in which a plurality of such transmitters are each allotted to a particular traffic area identified by a sub-audible frequency which modulates the subcarrier. The lowest frequency of the range of sub-audio frequencies is a message identification signal indicating the beginning and end of traffic information. At a co-operating receiver, the subcarrier is selected and supplied to a recognition circuit 1, which controls a selfseeking tuner and indicates that a traffic signal is being received, and is demodulated, the resulting sub-audio frequency f K being supplied via a Schmitt trigger 2 which converts it into a rectangular wave, to a monostable 3 which converts it into pulses of constant duration. These pulses are integrated at 4 so that a voltage U K proportional to the frequency f K is supplied via switch S to an indicating device 5 which includes a scale 7 composed of luminous elements 6. This scale carries markings for the traffic radio areas in addition to a normal frequency scale. Thus if the voltage U K is applied. instead of a tuning voltage U Abst of an electronically tuned receiver, the element 6 corresponding to the frequency f K of a traffic area will light up. Push buttons 8 may be operated so that only transmitters in particular areas will be received. The message identification signal is selected by a filter 9 and may be arranged to switch on and off a recording device.