GB1385850A - Receiver for a selective paging system - Google Patents

Abstract

1385850 Selective signalling PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 30 Oct 1973 [2 Nov 1972] 50318/73 Heading G4H [Also in Division H4] A receiver for a selective paging system includes a local clock signal generator which is automatically switched to supply an input to an acoustic warning device on receipt of the correct address signal for that receiver. By this means a separate tone oscillator is dispensed with, with consequent saving in weight. As shown, the transmitter 1 is provided with an address generator 3 by which the digits of a desired decimal number may be successively generated in binary form under the control of a clock pulse generator 4. The resulting signal frequency-modulates via modulator 5 a carrier wave generated at 6. The signal is of the type in which binary 1 has a high value in the first half of the bit period and a low value in the second half and binary 0 is the inverse thereof. At the receiver the received signal is frequency-changed at 8 and supplied via filter 9 and limiter 10 to a detector 12 and a phase discriminator 11. Phase discriminator 11 forms part of a phase-lock loop comprising clock pulse regenerator 14, filter 16 and divider 15. The clock pulses from divider 15 are supplied to synchronous detector 12 and the resulting address code is supplied to an address comparator 17 which on receipt of the correct address, as stored at 19, supplies a control signal at 18. This causes switch 22 to break and switch 21 to make to apply the output of the clock pulse regenerator 14 to the acoustic reproduction device 20. Switches 21, 22 may be electronic switches.