Patent GB-1175130-A (GB)
Title: Radio Communication System
IPC: H04W72/02
Filed: 1967-12-08
Abstract: 1,175,130. Multiplex radio signalling; interconnection system. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 8 Dec., 1967 [13 Dec., 1966], No. 55982/67. Headings H4K and H4L. The invention provides a system for intercommunication between radio transceivers without the use of a central station and using a common frequency band which is divided into two frequency ranges, a plurality of carrier frequencies being fixed in each range. The transmitter of each transceiver can be adjusted to any of these carrier frequencies and with each of these carrier frequencies there is associated unambiguously a carrier frequency in the other frequency range which is used by the corresponding receiver. As described there are twenty carrier frequencies spaced by 25 Kc./s. in each range and the spacing between the transmitting and corresponding receiver carrier frequencies is always 7À5 Mc./s. The transceiver, Fig. 1, includes a store 1 in which its own address signal is stored in binary code and an adjustable store 2 in which the address of the wanted station is stored. In the calling position the address signals are modulated on a subcarrier at 4 and supplied via changeover switch 5 to the P.M. transmitter 6. In the speech position of switch 5, signals from microphone 8 are amplified at 7 and supplied to the transmitter. Incoming signals are received at 9, demodulated at 10 and in the stand-by position of switch 11 are supplied to a subcarrier demodulator 12 whose output is regenerated at 13 and supplied to an address store 14. Circuits 15 and 16 which identify the station's own address and the address of a called station respectively are connected to store 14. In the speech position of switch 11, received signals are amplified at 17 and supplied to telephone 18. Standby position.-The transmitter is switched off and tuned to the reply band and the receiver is switched on and tuned to the call band, a multi-channel generator 20 controlled by a stepping oscillator 21 stepping the transmitter and receiver through the respective frequency bands. If the station's address signal is received it is recognized at 15 and through logic circuitry 23, Fig. 3 (not shown), the receiver is locked on to the relevant call channel and the transmitter locked on to the corresponding reply channel. The transmitter sends its own address and the switches 5, 11 are changed over for speech communication. To call a station.-The tuning is stepped as before and a free-channel detector 19 finds a free channel (by the noise level from the discriminator 10) and the transmitting and receiving bands are then interchanged by a device 22 so that the transmitter is tuned to the call band and the receiver to the reply band. After this changeover the detector 19 checks that the reply channel is also free. If it is not free the receiver is tuned back to the call band and the searching process repeated. Otherwise the transmitter is switched on and the address of the desired station (from store 2) is transmitted. The called station replies with its own address signal which is received at 9, stored at 14 and identified at 16 as that transmitted from store 2, after which switches 5 and 11 are turned to the "speech" position.