Patent GB-850698-A (GB)
Title: Improvements in and relating to radio signalling systems
Inventor: SPENCER HERBERT CYRIL
IPC: H04W48/16
Filed: 1957-11-21
Abstract: 850,698. Radio signalling. UNITED KING- DOM ATOMIC ENERGY AUTHORITY. Nov. 14, 1958 [Dec. 3, 1957], No. 36365/57. Class 40(5). In a system for enabling radio telephone communication to be effected between a telephone exchange and any one of a plurality of subscriberstations, wherein each subscriber station includes means for cyclically scanning a plurality of radio channels of different wave-lengths, the number of channels being less than the number of subscriber-stations, the telephone exchange is provided with means whereby a calling signal individual to a selected one of the subscriber-stations can be transmitted in a selected one of the radio channels, and each subscriber-station includes means responsive to the reception of its calling signal in any one of the channels to arrest the cyclic scanning of the channels in the channel in which the calling signal is received. In the embodiment described ten subscriber-stations in conjunction with one telephone exchange are provided with three radio channels of different frequencies. The exchange has an associated radio station with three transmitters and three receivers respectively tuned to the three frequencies. Each subscriber station has an individual code in the form of three tones of different frequencies which can be transmitted from the exchange in anyone of the channels to call the subscriber-station, and which can be transmitted from the subscriber-station to the exchange for identifying the subscriber-station. Figs. 2 to 5 show part of the equipment at the exchange including terminations, above the broken line 108, for four of the subscribers which each include a set of three relays such as AKA, BKA, CKA, for subscriber No. 1 for giving access to the channels A, B, and C respectively. A further relay set within a broken line 109 controls the radio apparatus at the exchange, and a relay set below the line 108 and outside the rectangle 109 is the channel A exchange control relay set, there being a similar set for each of the other channels. Calling subscriber-station from exchange assuming that the No. 1 subscriber is called, an earth is placed on wire P1 and if all the channels are free the relays AKA, BKA, CKA, are in the conditions shown and relay AKA will be energized and extends the speech connections -(1), +(1), from the exchange final selector to the Channel A exchange control set, and is followed by relay AGA. Terminals V, W, X, Y, and Z, are connected to five tone generators respectively, and contacts AKA6, AKA1, AKA8, connect terminals V, W, X, to a common lead 110 connected to changeover relay contacts OTA1. Operation of relay AGA closes a link in a chain AGA1, BGA1, CGA1, which gives a "busy" indication when all channels are in use, and is followed by relays OG and JG. The other subscribers' terminations are transferred to the channel B access relays BKB, BKC &c., and the speech wires +(1), -(1) are connected across the relay winding RGA via the split secondary winding W1 of transformer T1 A circuit is prepared for relay DR, and relay D is connected across a split secondary winding W2 of transformer Tl. The ringing current in wires +(1), -(1), will energize relay RGA but at this stage its contacts RGA1 are isolated by relay contacts DQ3. Relays D and RA become energized from the two-wire junction 111 followed by relays DR, RB, and RC. Contact RB2 connects the H.T. supply to the transmitter for channel A (not shown) and RB3 connects a relay FSA to a terminal FS. Relay DR is held and is followed by relay OTA, thus applying the selected tones from the lead 110 to the primary winding of transformer T1 The tones are applied via the twowire junction 111 and transformer T2 to the transmitter in channel A. At the called subscriberstation, Figs. 7 and 8, a scanning oscillator (part of which is shown at 115) causes the receiver to scan cyclically the channels A, B, C, by means of three oscillators which are switched on and off in a recurring sequence and produce the receiver intermediate frequency when mixed with the three carrier oscillations respectively. Threee triodes 13, 29, 49, are associated with the three oscillators, and are normally conducting but each is made non-conducting when its associated oscillator is switched on. The resulting anode pulse when a triode becomes non-conducting triggers a corresponding gas filled triode CCTA, CCTB, or CCTC. Striking of the triodes is normally prevented by relay contacts CP2, TR4, CA1, CB1, CC1, and RS2, but when the correct calling tones are received filters (not shown) pass the tones to energize relays VR, WR, and XR which are followed by relay TR. Assuming that the tones are received on channel A, valve 13 is non- conducting. Relay TR prepares a circuit for relay CP and is followed by relay CA, which is energized via CCTA, and by relay RS. The triodes 29 and 49 are disconnected, the transmitter and receiver are switched to channel A, H.T. is supplied to the transmitter whereby it radiates a carrier oscillation and. relay CP is energized. A circuit is prepared for relay RG. A conductor 116 is earthed to shift the transmitter frequency off its normal channel A value to provide an answering signal, and the subscriber's telephone is connected to a transformer T3 to modulate the carrier oscillations. Reception of the subscriber-station's carrier at the exchange energizes a relay RSA which at this instant has no function. The frequency-shifted carrier operates a relay FSA to reverse the battery connections to the two-wire junction 111, and release relay D which causes energization of relay DQ which is held, and prepares a loop to wires +(1), -(1). Relay OTA is released and stops the transmission of the tone combination to the subscriber station. At the subscriber-station, when the incoming tones cease, relays VR, WR, and XR release, followed by relay TR. At the exchange the relay RGA continues to operate intermittently in response to the ringing current and is followed by relay OTA whereby the tone combination is transmitted intermittently and causes intermittent operation of VR, WR, and XR, and RG 1 , at the subscriber-station. Ringing current is supplied continuously between terminals 119, 120, and the relay RG, Fig. 7 causes intermittent application of ringing current to the subscribers' instrument. When the called subscriber lifts his handset relay L is energized and followed by relay HL which closes an alternative circuit for the relay CA in the scanning oscillator. Contacts HL4 shift the transmitter frequency back to normal to indicate to the exchange that the subscriber has removed his handset. At the exchange the relay FSA releases and restores the normal connections of relay RA to the two-line junction 111, causing relay D to be energized to connect a loop across the wires +(1), -(1), and trip the ringing supply circuit to provide a "called subscriber answered" signal. Thus the communication circuits are set up. Termination of call. Assuming that the called subscriber replaces his handset first, the relay L releases followed by HL which shifts the carrier frequency once more. At the exchange relay FSA is energized on the occurrence of the frequency shift and reverses the connections of the relay RA to the two-wire junction 111 which releases relay D. Contacts D2 disconnect the loop from the wires +(1), -(1), to give a "called subscriber cleared" signal. When the calling subscriber replaces his handset the earth is removed from the wire P(1) and releases relay AKA which disconnects the wires +(1), -(1), from the channel A exchange control relay set. Relay AGA is released and opens the link in the "busy indication" chain AGA1, BGA1, CGA1, and restores the subscriber terminations P(1) &c. to their associated channel A access relays. Relay OG is released and releases relays DQ and DR, disconnects the loop including relay D from 111, and disconnects the battery from relay JG which continues to hold over an alternative circuit including OG4 and the upper half of relay RA. The current flowing is not enough to hold RA which releases, followed by relays RB, RC and FSA. The H.T. supply is removed from the transmitter and normal connection of relay RA is restored whereby relay JG releases. At the subscriber-station relay RS releases when the incoming carrier stops, followed by relays CP and CA. The subscriber's instrument is disconnected from the speaking circuit and the frequency shift removed. Contacts CA2, CA6, restore the H.T. supply to the valves 29, 49, and CA4 switches off the transmitter. If the calling subscriber replaces his handset first the earth is removed from P(1) as before, AKA is released followed by AGA, which opens the link AGA1, and OG is released, followed by DQ, DR, and JG, which connects relay LA to the two-wire junction 111. RA releases, followed by RB, and RC is de-energized. At the calling subscriber station RS releases when the incoming carrier stops, followed by CP and the subscriber's instrument is disconnected. The relay CA holds and the transmitter continues to radiate. At the exchange slow-release relay RC releases and connects the frequency shift terminal FS to the relay FSB. Relay IC is energized and connects a loop across 111 and energizes the transmitter through contacts IC3. Contacts IC5 prepare an impulse shunt circuit. At the calling subscriber station relay RS operates again in response to the incoming carrier followed by OT and slow-tooperate relay DS and contacts OT1 connect terminals VT, WT, and XT. to the transmitter. A tone generator (not shown) applies tones individual to the subscriber station to the terminals. At the exchange, relay LA is energized and closes a circuit for relay LB which through contacts LB1 connects a loop across the + and - wires extending to the channel A control relay set, and prepares a circuit for relays OTA, DSA, and TRA. The tones received from the subscriber station operate relays VX, WX, XX