GB842315A - - Google Patents

Abstract

842,315. Radio signalling. TELEFUNKEN G.m.b.H. June 21, 1956 [June 21, 1955], No. 19321/56. Class 40(5). A radio communication selective calling system comprises a main station and substations in which a substation receives call signals in a first code system and transmits call signals representing a desired connection with another station in a second code system; the main station transmits a group of tones simultaneously characterizing the substation called, the substation sequentially retransmitting tones different from the main station transmission thereby effecting the desired connection with the main station. All the tones are generated at the main station, the call signal operating resonant relays at the substation, and series resonant circuits selecting the different frequency combinations for retransmission as a call signal from the substation. At the substation the low frequency output of a known receiver is applied to terminals 1 and 2, parallel resonant relays 3-7, and series resonant circuits 8-12 separating the signal frequencies transmitted from the main. station being connected as shown, the resonant frequencies of set 3-7 and set 8-12 being in mutually non-interfering ranges. In the tapped leads of circuits 8-12 are relay contacts 13<SP>1</SP>-17<SP>1</SP> of relays 13-17 through which the transmitted signal frequencies can be applied, individually or in groups to the modulator of the transmittor by terminal 18. When a substation calls another substation, a call signal sent from the substation to the main station causes interruption of the "free" signal normally sent from the main station, which immediately transmits a modulated carrier to provide calling frequencies for the calling substations. The substation transmits a characteristic responding signal comprising a sequence of industrial frequency combinations derived from frequencies sent by the main station, and set up at the substation by stepping switches 21 appropriately connected to provide the required frequencies. In position 1 of switch 21 relays 13 and 16 operate to close contacts 13<SP>1</SP> and 16<SP>1</SP> and the two frequencies derived from circuits 8 and 11 are applied to the transmitter, each successive movement of switch 21 selecting and similarly applying two frequencies to the modulators which together all constitute characteristic code. Delay-operating relay 23 operates simultaneously with slow releasing relays 13 to 17 to produce a signal of a given length on each operation of switch 21. The main station sends a modulated signal requesting the substation to identify the station being called. The calling station dials the number operating selector 21 and through relay 22 operating in a similar manner to relay 23, a carrier modulator with successive frequency combinations is transmitted. The main station then transmits a code signal to call up the required station via its resonance relays and thereafter a speech channel is set up. Specification 838,013 is referred to.