Patent GB-436624-A (GB)
Title: Improvements in and relating to telegraphic trunk switching systems
IPC: H04M11/06
Filed: 1935-02-11
Abstract: 436,624. Exchange systems. SIEMENS & HALSKE AKT.-GES., Siemensstadt, Berlin. Feb. 11, 1935, No. 4370. Convention date, Feb. 9, 1934. [Class 40 (iv)] In a system in which telegraphic connections are set up partly over a telephone system and partly over a purely telegraphic system and in which telegraphy, is transmitted over the telephone system by voice frequency signals, clearing indicators are provided at a junction point (exchange) between the telephone and telegraph systems and the indicator for the telephone portion of a connection is operated by a signal automatically transmitted when the telephone subscriber initiates the release of the telephonic portion of the connection. The invention is described with reference to telegraphic connections set up by telephone subscribers having teleprinter facilities, the telephone system comprising automatic or manual exchanges, and the clearing signal consisting of a pulse of alternating current of the frequency used for telegraphy, or for a supervisory telephonic signal, or otherwise, transmitted from the telephone exchange or from the telephone sub-station. Automatic telephone connection to the junction point ; clearing signal transmitted from exchange, Figs. 1 and 2. The telephone connection is set up over switches VW, GW and repeater Ue1 to a trunk FFL leading to the junction point, Fig. 2, where the connection is manually extended over a cord circuit to the telegraphic trunk TFL, leading to a telegraph exchange. The cord circuit comprises means, US1700, for converting audio-frequency to D.C. telegraphy and means, US350, for receiving the clearing signal which in this case is of different frequency from the telegraphy. The D.C. telegraphy may be again converted at UT into sub-audio or other signals for transmission over the telegraphic trunk. The telephone connection is set up in known manner except that an impulse repeater Z is interposed in the subscriber's line circuit and serves also to apply the clearing signal when the calling loop is opened at the end of a transmission. When a call is initiated, relay A at the repeater operates X, and V1 which is slow-to-release and is followed by another slow relay V2 to close an outgoing loop to start the line switch VW. The digit is now dialled, the relapse of A on the first break releasing X to make a circuit for an impulse controlling relay IH which is quick to operate but has a release period of 60 milliseconds, and operating slow releasing relay B which short-circuits transformer Ub in the outgoing loop. When the impulse ceases the re-operation of X energizes I which breaks the outgoing loop and holds itself dependent on IH which relapses after 60 milli-seconds so that the break impulse repeated by I is independent of the make periods of the incoming impulses. A register-controller may replace the relay repeating set. When the call has been extended to the incoming repeater UF, Fig. 2, at the junction point, lamp ALF lights and an operator attends to the call using a set FA associated with the repeater or by plugging in and using a set associated with the cord. On plugging in, sleeve relay C2 prepares circuits for the clearing lamps SL1, SL2, the connection being extended over jack TKL and the telegraphic trunk TFL, whereupon Y2 operates W2 and holds itself. The telephone subscriber is signalled automatically or by the operator to prepare for teleprinting by throwing switch U and replacing his receiver. On termination of a transmission, the clearing signal on the telegraphic side is given by a long minus which releases Y2 to light lamp SL2. On the telephone side, the subscriber opens switch U to break his loop and release A, whereupon X, VI, V2 fall back in turn and during the release period of V2, 350 cycle A.C. is transmitted over transformer Ub and operates Y1 in the cord circuit at the junction point. W1 pulls up, locks, and lights lamp SL1. At the automatic telephone exchange, V2 maintains a holding loops until it terminates the clearing signal, whereupon the switches are released in the usual manner. If it is desired that the release signal should also pass to a distant telegraphic exchange, a long pulse of the telegraphic frequency is transmitted from the telephone exchange in which case the apparatus US350, Fig. 2, is dispensed with and relay Y 1 is operated from the transmitting channel in the cord circuit in a similar manner to Y2. Clearing signal transmitted from sub-station, Fig. 4. After connection has been established as previously described, the subscriber throws switch U to operate HU which connects up the teleprinter apparatus. The A.C. source comprises a valve oscillator connected to line over transformer Ue, signalling being effected by contacts sk which short-circuits a winding of transformer SU. Opening of the short-circuit when switching in is prevented by switch contact u3. Incoming signals over Ue are transmitted over transformer EU to receiving apparatus EV, EM. The subscriber initiates release by restoring key U so that HU falls back slowly. During the release period of HU, the short-circuit over key SK is open and an additional tuning condenser C2 is connected in the oscillator so that a pulse of a frequency different from that used for telegraphy is sent out and lights lamp SL1, Fig. 2, as previously described. Manual telephone exchange system, Fig. 3, in conjunction with Fig. 2. Relay AR lights calling lamp AL which is extinguished by TR when the operator answers, sleeve relay S being short-circuited by AR and TR. The operator sets up the connection to the exchange at the junction point in the usual manner and the subscriber connects up his teleprinter over switch U. On termination of the transmission, restoration of U opens the calling loop and the relapse of AR permits S to pull up over TR. Relay S operates SH and a slow operating relay VH which opens the circuit of SH so that during the operating period of VH, SH connects an A.C. release signal to the line with results at the junction exchange as previously described. Supervisory lamp SL3, Fig. 3, also lights up to signal the local operator.