Patent GB-864412-A (GB)
Title: Improvements in or relating to telephone systems
Inventor: WATSON FREDERICK CHARLES STRAT
IPC: H04Q1/50
Filed: 1956-07-25
Abstract: 864,412. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd., and BRITISH TELECOMMUNICATIONS RESEARCH Ltd. July 3, 1957 [July 25, 1956], No. 22937/56. Class 40 (4). Signals are transmitted over a bothway interexchange radio link as frequency shifts between a speech carrier frequency and a second frequency. Different pairs of frequencies #1, #2 and f3, f4 are used for the two directions. A loop condition at a calling exchange signals a call to automatic equipment at a second exchange. A leg signal signals a call to a manual board at the second exchange. A call from an ordinary subscriber is signalled on one leg and a call from a coin-collecting box station (C.C.R.) is signalled on the other. In the system described, a unit automatic exchange (U.A.X.) is linked by radio to a main exchange with both manual and automatic facilities. The link is terminated by relay sets RLRS, Figs. 1, 2, and 1RLRS, Figs. 3, 4, in the respective exchanges. Manual hold and trunk offering facilities are described. Call to manual board from ordinary subscriber at U.A.X.-The subscriber gains access to the link by dialling O. In response to battery on the + lead of line BWRS the transmitter TMTR starts on frequency f1, shifts down to f2 and returns to f1. Relay LA comes up in response to the leg signal and B follows. The transmitter TMTR transmits on frequency f1 when lead 10 is grounded over 1a4. Relay DS comes up after a delay and is disconnected by slow-to-operate FS which also operates indicator lamp IP, brings up SC and connects lead 11 to TMTR to drop the frequency to f2 for a period determined by FS, DS. When the frequency f1 is received at the radio link relay set 1RLRS of the main exchange, relay 1RS comes up, connects ground at irs2 and is followed by 1CRS, DRS. Relay 1BRS follows 1CRS, after a delay, and loops the line PEQ to the main exchange and connects the line to the hybrid transformer 1HY. Supervisory lamp 1LP indicates that the radio link relay set 1RLRS is busy. A slugged timing relay AT is energized when 1RS comes up but, in this call, is disconnected before it can pull up. Relay 1SD responds to the frequency shift f1 down to f2 and DU follows slowly, to disconnect AT. Relay DU locks and at du6 breaks the loop on line PEQ thereby releasing the automatic equipment seized when the line was originally looped. Relay AM follows DU slowly enough for the frequency received to revert from f2 to f1 and for 1SD to fall back before AM comes up. Relays SG and 1DD follow AM in sequence the battery energizing 1DD over R6 being extended over the + lead of PEQ to seize the equipment giving access to the manual board. Relay SG locks to 1RS and DB follows 1DD. At this stage the calling subscriber is receiving ringing tone and the operator a lamp signal. When the operator replies, relay 1DD falls back, J comes up and locks to DU, and DB is de-energized. Relay J is followed by 1SC which connects lead 12 to 1TMTR to start transmission on frequency f3. Ground is extended through relay 1D over the - lead of PEQ to the manual board equipment which returns battery on the + lead to bring up 1DD again and to reconnect DB in time to keep it up after de-energization. On receipt of an answer signal of frequency f3, receiver RCVR in the U.A.X. responds and relay RS comes up followed by BRS, CRS with a delay. Relay CRS connects the line BWRS to the hybrid HY and disconnects relays LA, LB, but these are reconnected by CH when the relay set connected to the other end of line BWRS responds to the disconnection of ground from the + lead at crs5 by returning earth on the - lead. The link is now ready for speech. Manual hold.-The operator may ask the caller to clear. The caller can recall the operator until the operator clears. When the caller clears potentials are removed from both the leads of line BWRS and transmission of frequency f1 by TMTR stops. Relays RS, BRS, CRS, CH remain up dependent upon receipt of f3 from the main exchange and the line BWRS remains connected to the hybrid HY. At the main exchange relay set 1RLRS, relay 1RS falls back on cessation of f1. Relays 1DD, 1D, DRS, 1CRS &c. fall back leaving 1BRS, DU, AM, SG held at first to DRS during the delay in release and subsequently to 1MH. Relay 1MH comes up when the manual board returns battery over the + lead in response to disconnection of R6 and battery on clearance. Recall.-If the caller recalls, battery is connected to the + lead as before and, in addition, ground is connected to the - lead. Relay MH comes up and is followed by B which trips MH. Relays LA, LB come up and B locks to LA. Transmitter TMTR transmits frequency f1 again but as LA, LB come up together, DS has no time to operate and there is no frequency shift down to f2. At the main exchange, relay 1RS comes up in response to f1, 1MH falls back and DRS, 1CRS come up as before. Ground is connected through 1D to the - lead of PEQ to give a recall signal to the board. Ground is returned on the + lead to bring up 1DD and the link is again ready for speech. Operator clears.-If there is no recall and the operator clears, battery is removed from the + lead of PEQ and relay 1MH goes back followed by 1BRS, DU, AM, SG, J and SC and transmission of f3 ceases. In the circuit RLRS at the subsidiary exchange, RS goes back and is followed by BRS, CRS, CH as the circuit returns to normal. Call from coin-collecting box station.-The subscriber dials O to gain access to the link as before. In response to ground on the - lead of BWRS, the transmitter TMTR starts on frequency #2 and shifts down to #1. Relay LB comes up in response to the leg signal and CB follows before B. The operating delay of DS is lengthened by capacitor C5 so that the frequency shift f1 to f2, controlled by FS, takes place before SC comes up to start the transmitter. The frequency shifts back to f1 when DS eventually comes up. Relay RDS comes up and locks to CB and relays FS, DS fall back in sequence. In the main exchange, frequency f2 brings up 1RS which is followed by 1CRS, DRS, 1BRS to loop the line PEQ and to connect the line to the hybrid HY. Relay SU responds to the shift f2 to f1 but soon relapses. Relays RU, DU follow slowly, RU interchanging relays ID, 1DD between the two leads of line PEQ without changing the potentials applicable to the leads. The loop on PEQ is broken at du6 to release the automatic equipment and relays AM, SG come up, ground being connected through 1DD to the - lead of PEQ to signal the manual board. Relays 1DD, DB come up but go back when the operator replies and disconnects battery from the - lead but J comes up in the delay period of DB. Battery is connected over j1 and 1D to the + lead of PEQ to signal the manual board which responds by returning battery over the - lead to bring up 1DD again. Relay 1SC which follows J starts transmission of f3 from 1TMTR. The link is ready for speech when the circuit RLRS responds to f3 substantially as in a call from an ordinary subscriber. In this call, however, the relay set connected to the other end of line BWRS is signalled over the - lead when LB and battery are disconnected by CRS. Battery is returned over the + lead to bring up CH over its lower winding. Manual hold facilities are described. Call to automatic equipment.-When the radio link circuit RLRS is seized from the ninth level of a first digit selector, the line BWRS is looped and relays LA, LB come up together. Relays CD, CDR, DD, SC and P come up in sequence, the transmitter starts on frequency f1 and relay A is substituted for LA, LB in the line BWRS. Relay SW extends the line BWRS to the hybrid HY. At the main exchange relay 1RS responds to f1 and is followed by 1CRS, DRS, 1BRS to loop the line PEQ and seize the automatic equipment as before. As there is no shift to f2, relay AT is allowed to operate after a delay and brings up SG. Relay SG replaces the seizing loop through R4 by a loop through relays 1D, 1DD in which only 1DD comes up. The second digit is dialled and relay A in relay set RLRS repeats each impulse as a frequency shift from f1 to f2 to #1. At the main exchange the impulses are repeated by 1SD which transmits them over PEQ to the automatic equipment. Relay 1CD brings up CA, ATR. Relay 1SC connects lead 12 to the transmitter 1TMTR which transmits frequency f3. After dialling, the appropriate tone is returned over the radio link. On reply, battery reversal brings up 1D, 1FS, DT and the signal is transmitted over the radio link as a shift down from frequency f3 to f4 as lead 13 is connected to the transmitter 1TMTR. The signal ends when DT trips 1FS and the circuit is ready for speech. If the called party clears, 1D falls back and 1FS drops the frequency of 1TMTR from f3 to f4 during the delay on release of DT. At the calling exchange SD responds to f4 and DJ comes up for a time to reverse battery on line BWRS. When the calling party clears A falls back and the frequency of TMTR drops from f1 to f2 and transmission stops. At the main exchange, 1SD responds to the shift f1-f2 and breaks the loop in PEQ to release the automatic equipment. When the transmission stops the circuit returns to normal. Call from main exchange to U.A.X.-When line PEQ is looped, relays 1A, 1B, 1BB, RBB, ISC come up in sequence and transmitter 1TMTR transmits on frequency f3. At U.A.X., RS responds to f3 and is followed in sequence by BRS, BA, BB, RBA, SC, P and SW. Frequency f1 is transmitted back by TMTR when SC comes up and the line BWRS is looped by P to seize the equipment available over the line. Relay SW connects the line BWRS to the hybrid HY and 1L comes up in the direct-current loop. The main exchange circuit 1RLRS is built up as before on receipt of f1 and dial tone is returned from U.A.X. over the link. On dialling, relay A falls back and the frequency of 1TMTR shifts from f3 down to f4 for the " break " period of each impulse. At the U.A.X. relay SD comes up during each impulse of f4