Patent GB-533371-A (GB)
Title: Improvements in or relating to teleprinter exchange systems
IPC: H04L12/04
Filed: 1939-08-11
Abstract: 533,371. Telegraph exchange systems. STANDARD TELEPHONES & CABLES, Ltd., HARTLEY, G. C., and HYDE, G. A. M. Aug. 11, 1939, No. 23280. [Class 40 (iii)] Relates to teleprinter exchange systems having repeaters at the exchange. (1) In systems comprising single-current and double-current lines, a two-way repeater in the connecting circuit which converts single-current signals into doublecurrent signals has its circuits altered when connection is made with a double-current line, so that such double-current signals are not repeated thereby but are transmitted directly through the connecting circuit to the other line ; (2) In systems using double-current working, an operator's monitoring teleprinter can be connected to the connecting circuit in such a way as to record signals sent to, as well as those received from, a line, this being effected by providing means in the circuit of the line for repeating back into the connecting circuit signals received over the connecting circuit. The invention is applicable to automatic systems but is described as applied to a manual system, Fig. 1 showing a sub-station and terminal equipment of a singlecurrent line, Fig. 2 the cord circuit equipment, and Fig. 3 the terminal equipment of a longdistance line. Interconnection of two lines using singlecurrent working. A sub-station calls by depressing key CK, Fig. 1, which causes relay L to light lamp CLL. The insertion of the answering plug AP closes a circuit for the repeater relay TR over the tip of the plug and line 2, and at the same time a circuit is closed from the armature tr1, over contacts of monitoring keys, contacts fs2, bs5, resistance R1, relay BF, line 1, motor relay MS and teleprinter magnet TPM to earth. Relay MS starts the teleprinter motor. By depressing monitoring key A or B (the contacts of which are shown in various parts of Fig. 2), the operator connects up her printer PTMI or PTM2 to the circuit controlled by armature tr1 (traced above), so that the calling party can record in the operator's printer the number of the wanted line. A record of this number is made at the calling station, since armature tr1 also repeats it over line 1 to the sub-station printer magnet TPM, Fig. 1. The operator inserts the calling plug in the jack of the wanted line, and if this line is one using single-current working, the sleeve relay FS is not energized, and the relay TR is connected to the line 2 of both calling and called stations. Signals sent by either party are thus repeated by armature tr1 to the other party over line 1, and also, as long as the monitoring key is depressed, to the operator's printer PTM1 or PTM2. Clearing and supervisory signals. When the operator inserts the answering plug, the potential across resistance R1 energizes relay BL to light lamp BSL. The depression of either monitoring key removes a short circuit around relay BC, which short-circuits BL to extinguish lamp BSL. The calling party gives a clearing signal by opening contact CLK which releases relay BC ; when contact CLK is restored relay BL lights the lamp BSL. The sub-station can call in the operator by closing contact RK thereby reducing the line resistance sufficiently to energize relay BF which connects lamp BSL to an interrupter. The lamp FSL is controlled similarly by the relays FC, FL, FF. Connection from single-current line to line using double-durrent working, Fig. 3. The sleeve of the jack of such a line is earthed through a relay SL, so that when the calling plug is inserted, relay FS energizes and alters the circuits of the cord. (The line shown in Fig. 3 is assumed to be one over which signalling takes place by voice-frequency currents and signals received over the line are converted into doublecurrent signals, by means not shown, to operate polarized relays B, SS. Similarly signals to be transmitted over the line are double-current signals from contacts a1 of relay A, which are converted by means not shown into voicefrequency signals). Signals from the calling line are repeated by relay TR over contact tr1, contacts bs2, bs3, ring of plug to relay A, Fig. 3, which repeats them to the called line. Signals from the called line are repeated by relay B, Fig. 3, over the tip of the calling plug, contacts fs1, fs2 (in their operated position), ring of answering plug, and line 1 to calling station. A branch from this circuit over contact bs4 leads to the operator's printer if either monitoring key is depressed. Connection between two double-current lines. In this event relays BS, FS are both energized, and relay TR and its armature tr1 are completely disconnected at bs1, fs1, bs7, fs7. Signals from the calling line are repeated by relay B over the tip of the answering plug, contacts bs1, bs2 (in their operated position), key PFK, ring of calling plug, to relay A of the called line, which repeats them as voice-current signals to the called line, and also as double-current signals over the tip of the calling plug and contacts fs1, fs2, bs4, fs4, to the operator's printer. Signals from the called line are repeated over a similar circuit over contacts fs1, fs2, bs5, fs5, monitoring keys, contacts fs6, bs6, the ring of the answering plug to relay A of the calling line. A branch from this circuit over contacts bs4, fs4 (in their operated position) leads to the operator's printer. In order to prevent signals from the calling line repeated back into the connecting circuit by relay A of the called line from being returned into the calling line, relays SA, SS, Fig. 3, are associated with relays A, B, relay SS causing the slow-release relay SA to disconnect relay A from the jack while the relay B is receiving signals. Specifications 429,095, 498,416 and 531,902 are referred to.