GB811224A - - Google Patents

Abstract

811,224. Radio signalling. PHILIPS ELECTRICAL INDUSTRIES Ltd. Jan. 30, 1956 [Jan. 29, 1955], No. 2915/56. Class 40 (5). A radio system comprises a main station and substations in which when a substation calls the main station a control signal higher than the normal audio band is sent which causes the main station to transmit a blocking signal to the other stations, these substations being subsequently unblocked by a releasing signal transmitted by the main station. In the main station, Fig. 1, transmitter 1 and receiver 2 operating on different carrier frequencies are connected to aerial 4 by switch 3. The receiver output is applied via low-pass filter 9 to hybrid circuit 6. balanced by balancing impedance 5, the transmitter and receiver thereby being connected to telephone instrument 8. A filter 9 cuts off a control signal located above the speech-frequency band, which is applied to control signal receiver 10, and thereby to switch 11 and blocking signal generator 12. Switch 11 energizes the transmitter 1 and generator 12 and thus the transmitter radiates a blocking signal. The keying generator 13 is connected to switchboard 7 keying the transmitter and switches on the releasing signal generator 14 when exchanging device 7 is at the rest position. In the substation, Fig. 2, the transmitter 15 and receiver 16 are connected by relay 17 and 18 to aerial 19. The output of receiver 16 is connected to a switch 20, blocking or releasing the substation on receipt of the appropriate signal. When released the output of receiver 16 is connected through loud-speaker 21 and telephone receiver 22. When switch 23 is closed, the switch 20 energizes control signal generator 24 modulating transmitter 15 and relay 18 operates. A wavechange switch 25 connected to the switch 20 blocks the receiver until receipt of the releasing signal of that station, if it is switched manually to a second main station. To prevent misuse a retarding relay 26 energized by switch 23 connected. to switching device 20 disables the transmitter if 23 remains closed for a predetermined time. Specification 720,699 is referred to.