Patent GB-499832-A (GB)
Title: Improvements relating to telephone systems
IPC: H04M3/40
Filed: 1937-07-29
Abstract: 499,832. Exchange systems. SIEMENS BROS. & CO., Ltd., and HUMPHRIES, H. E., and HENSLER, B. A. July 29, 1937, No. 21004. [Class 40 (iv)] In a system in which junctions or trunk lines of different classes as regards transmission losses and of different types, e.g. repeatered or not, two-wire or four-wire, are used for tandem connections, modification of the speaking circuit in terminal equipment associated with one line is effected by a relay, individual to the equipment, operated and held over a through wire from corresponding equipment associated with the other line in response to a class or type signal applied thereat. The terminal equipment may be permanently associated with the line or may be reached over non-numerical or numerical switches used in setting up the connection in which case it also receives a class or type signal from equipment individual to the line. In the arrangements described, the through connection comprises an extra pair of wires which are used for transmitting the signals and also, when such connection is on a four-wire basis, for speech. A repeater for use with a two- or four-wire connection is also described, the four wires being used in parallel pairs for four-wire working. Manual system, Figs. 1, 2 and 3. The terminal arrangements for incoming and outgoing lines are shown in Figs. 1 and 3 respectively, the manual board being represented by Fig. 2. If one or both of the incoming and outgoing lines are not repeatered at the exchange the through connection comprises a two-wire circuit +, -, the additional pair N +, N - being used only for signalling and control purposes, but if both lines are repeatered at the exchange, the additional pair is also used for speech, through transmission being on a four wire-basis. An exchange repeater for connection between a two-wire line and either a two- or four-wire line is described in a subsequent paragraph. The pairs at each terminal have resistance pads NP, LP and also compensating and terminating resistances YV.. YZ which can be cut in and out of circuit for purposes that will appear later, the central portion of the through connection being isolated by condensers Q to confine the D.C. class and type signals, speech being excluded from the signalling equipment by chokes R, RA. The signalling arrangements shown at the top of Figs. 1 and 3 comprise a number of alternative connections made over strappings CN1-CN9 in accordance with the class or type of incoming and outgoing line, the N wires being crossed in the connecting circuit so that for example. a ground signal in Fig. 1 operates a relay in Fig. 3, and vice-versa. Terminal equipment permanently associated with a line may have only the relevant permanent connections. Class 1 or high grade lines always have an amplifier at the exchange and strappings CN1, 2 and 3 are connected for such lines. Class 2 or intermediate grade lines have strappings CN1, 2 and 4, connected if they have an amplifier at the exchange and CN6, 7 and 8 if not. Class 3 or low grade lines have strapping CN2, 4 and 5 connected if they have an amplifier at the exchange and CN7, 8 and 9 if not. Various relays of which only contacts are shown are described in Specification 499,821. Relay SA (not shown) is operated at an early stage on all calls except when signalling is used, and relay D (not shown) is the reply relay. From the above it will be seen that for a Class 1 line, pad control relay PC(i) is connected to N- and four- or two-wire discriminating relay FW has both winding in series connected to N+. Pad control relay PC(i) will operate to cut out the pads at its own terminal if the N+ wire at the other terminal is connected directly to ground by strapping CN9, that is at a Class 3 terminal. Relay FW will only operate over windings (i) to make the connection a four-wire one if the N- wire at the other terminal is connected to battery over PC(i) or over PCA that is at the terminal of a Class 1 line or of Class 2 or 3 with an amplifier at the exchange. Relay FW in switching through the N wires, disconnects a balancing resistance YV (pad NP may be part of the balance) and at the same time removes a terminating guard-resistance YW of the connecting portion of the N wires. If the FW relay at one terminal is operated the conditions are such that the FW relay at the other terminal is also operated. If Fig. 1 were a Class 2 or Class 3 line provided with an amplifier at the exchange, auxiliary pad-control relay PCA would pull up to operate pad control relay only if the other terminal, Fig. 3, has ground connected direct or over resistance YA on the low resistance winding of FW, that is if it is Class 3 with an amplifier or Class 2 or 3 without one. At terminals of Class 2 or 3 lines without amplifiers, PCA pulls up in any case over a local circuit and PC cuts out the pads. If voice-frequency signalling is used, the circuit of PC or PCA is not completed until D operates on reply, the pads are therefore retained during the setting up of the connection to prevent undue shunting of the voice-frequency receiver connected at SFR. Relay AS is one operated by the operator's speak-key and CT (not shown) is operated when certain tone signals are to be transmitted, e.g. from wires BTW by the operation of TN (not shown). Relays AX, AY (not shown) are relays operated when the circuit is in use except during voicefrequency signaling when signals received at SFR are repeated in D.C. form over BTQ, a terminating resistance YY being connected up at this time. Another terminating resistance is disconnected by S, SP (not shown) when the line is in use. Two-way repeater, Fig. 4, for connection between a two-wire circuit and a two- or fourwire circuit. The two-wire line is connected to terminals LA, LB and the usual balancing network to terminals BLA, BLB, and if the repeater is to work into another two-wire line, e.g. the lines +, -, Fig. 1, this is connected to terminals TA, TB and terminals TNA, TNB are connected to a balancing network. If however it is to work into a four-wire line, the terminals TNA, TNB are connected to a pair of speech wires, e.g. N+, N-, Fig. ], and similar connections are made to another repeater over +, -, N +, N-, Fig. 3. The four-wire circuit is not the usual one having two wires for each direction. The output of valve VN is transmitted over two parallel circuits TB, TNA and TA, TNB which provide no input for the opposite valve VO of the same repeater but provide an additive input to the valve VO of the other repeater. Equalizers OEQ, NEQ and volume control potentiometers are provided in the valve input circuits and monitoring connections are taken off at MTL, MTC, MTT. Application to call distributing system, including call-box discrimination, Figs. 5 to 7. Incoming lines which may be Class 2 or 3 without repeaters at the exchange are connected over line switches, Fig. 5, and distributers, Fig. 6, to operators' connecting circuits, Fig. 7, including outgoing selectors having access to lines of any class. Terminal TM is disconnected or grounded over CN10 for a Class 2 ordinary or call-box line respectively, and is connected to high or low resistance battery over CN11 or CN12 for corresponding Class 3 lines. Relays Hand B (not shown) are the usual switching and release relays and HA, BA are relays which slowly follow the H and B relays, so that a momentary circuit is set up from TM over CO(i) to PC(i) which gives a Class 3 signal over wire N-. If PC is unoperated the signal on N- over resistance YT is a Class 2 signal since YT is made equal to the resistances of YA and choke RA, Fig. 1. When PC is operated to connect up YS in parallel with YT the resistance approximates to that from ground over choke RA, Fig. 1, which is the Class 3 signal. If, in the case of a delayed call, the operator sets up a connection hack to the calling party over wires RCW the necessary signals are received over the N wires of the revertive connection. In the case of a call-box line, CO is operated over (i) in the circuit described above when strapping CN12 is made (Class 3) or over (ii) and strapping CN10 (Class 2) when HA operates. CO connects tone from COT to the operator who removes it by grounding the + wire to operate TC.