Patent GB-348545-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1930-02-12
Abstract: 348,545. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. and SKILLMAN, T. S., Columbia House. Aldwych, London. Feb. 12, 1930, No. 4740. [Class 40 (iv).] In two-way working over inter-exchange junctions, calls in one direction are set up by a single coded impulse of alternating current for each digit and, in the other direction, by alternating current impulses in response to dialling. Coded impulses may be used in both directions, but this is not described in detail. In the system described, calling and supervisory signals in both directions comprise coded impulses of alternating current, calls from exchange A to exchange B being set up by keyboard operator AOP, Fig. 1, coded impulses of frequencies W .. Z being sent over the junction to operate relays BAW .. BDZ, Fig. 2, which energize direct current relays BEW .. BHZ to repeat the digits over leads 66 to registering and controlling mechanism (not shown). Calls from B to A are set up by operator BOP by dialled impulses which are repeated over the junction in the form of alternating current impulses of frequency W which are repeated at exchange A by relays AAW, AEW to impulse relay 31 for setting automatic switches directly or through a register-controller. Arrangements are provided for dealing with simultaneous seizure of the junction from both ends and preventing simultaneous transmission of signals in opposite directions. Special repeating coils A9, B9 for the signals are also described. Call from exchange A to exchange B. When the operator plugs jack 14 sleeve relay 10 opens the circuit of relay 13 to prevent a call in the opposite direction from being effective, energizes A3, A6, 22 and slow-to-pull-up relays 21, 25. Relay 21 operates 24 which connects voice-frequencies W, Z to transformer 29 and operates A8 so that a calling signal of these frequencies is sent over the junction during the release period of 22. At exchange B, relays BAW, BDZ, BEW, BHZ pull up and normally operated relay B3 falls back. Relay 53 now energizes, connects the junction to registering and controlling mechanism at BAE for extending the connection, and places busy tone on position BOP. Relays B6, B1 also pull up, and B6, 53 are held by B1. When the call signal ceases, B3 re-energizes and grounds lead 64 to prepare equipment BAE, and when BAE is ready to receive impulses it returns ground over 65 to energize slow-to-release relay 42 and slow-to-operate relay 51 which releases 42, so that 40 is transiently operated to energize B8 and connect voice-frequencies WY over transformer 69 to the junction. Relay 52 also pulls up. At exchange A, relays AAW, ACY, AEW, AGY respond so that A3 falls back and releases A6 which opens a loop across the tip and ring conductors and lights the supervisory lamp. The operator throws sending key 15, presses out the number on key-strip 19, and the resultant pulses of various combinations of frequencies W .. Z are clipped by relays 18, 17. The voicefrequency relays BAW .. BDZ at exchange B respond and the resulting operations of relays BEW .. BHZ ground leads 66 to the registering and controlling equipment. As soon as the number has been registered, a relay (not shown) connects ground from 63 to operate 49 which locks to the contact of B1 and releases 52. When the connection has been extended to the wanted line, and the called party replies, battery connected to the a wire operates 47 so that 46, 45, 42, 41, B8 pull up in turn and frequencies W, X are sent over the junction during the release period of 43 which had previously been energized. At exchange A, the W, X relays respond, normally operated relay A4 relapses, A6 energizes, extinguishes the supervisory lamp, and operates A3 which holds A6. Release. When the called party replaces his receiver, 47, 46, 45 fall back and 40 pulls up to connect frequencies WY to the junction during the release period of 42. A3, A6 fall back and the supervisory lamp glows. When the operater withdraws 10, 21 release and 27 connects up a long pulse of frequencies WY during the successive release periods 26, 28. Relay 25 falls back when 28 releases. At exchange B, all relays relapse except normally operated B2, B3, B5. Relay 21 cannot reoperate until 27 releases after sending out the release signal. Wanted party busy ; call offered by an operator at exchange B. Busy flash intermittently releases 47, 46 and therefore intermittently energizes 45 which operates 42 and releases 43 so that pulses of frequency WX are connected up by 41 during the release of 43 and pulses of WY are connected up by 40 during the release of 42 when 45 is deenergized. Slow-to -operate relay 45 compensates for the delay by 46. These pulses flash the supervisory lamp at exchange A as will be understood from a previous paragraph. The operator at A may call the operator at B by sending out ringing current to operate 12 which energizes 23 to connect a pulse XZ to the junction whereby the X, Z relays at exchange B respond to release B5. Relay 48 brings in over 67 an auxiliary operator who has braking-in facilities. Call from exchange B to exchange A. When operator at BOP plugs jack 61, relays, 60, 59, 47, 46 pull up and a pulse WX is sent out by 45, 42, 41 as previously described to release A4 and operate A6 which, by operating A3, locks up. Relay 13 connects the junction to automatic equipment AAE. When A4 relapses, A7 pulls up and energizes 31 which prepares the repeater AAE. The operator throws key 54, and impulses from dial 62 are followed by relay 47, which repeats the impulses to 38, 39. Relay 38 remains energized during the trains and 39 connects pulses of frequency W to the junction. Relay B8, operated in series with 39, is arranged to operate quicker than 39 so that the first pulse is not clipped. At exchange A relay AEW repeats the impulses to 31. Frequencies other than W operate A5 which holds 31 so that combinations containing W do not affect 31. When the called party replies, answering supervisory relay 30 operates and connects ground to 21 which operates 24 and releases 22 which had previously been operated by A6. As 25 is not now operated, 24 sends out a pulse WX and normally operated relay B2 relapses. Relay B6 energizes B1, locks and connects retard B7 to relay 57 which extinguishes the supervisory lamp. When the party at exchange A hangs up the receiver, relay 21 falls back, releases 26 and operates 27 to send a pulse WY which releases B1, B6 so that the supervisory lamp lights up and the operator withdraws and releases 47, 46. The consequent relapse of 45 sends back a long pulse WY during the release period of both 44, 42, relay 44 having been operated since 53 is not operated during the call. At exchange A, all relays except A4 relapse. Wanted party busy. Intermittent operation of answering relay 30 is repeated to relay 21 which causes pulses of frequencies WX, WY to be sent back to flash the supervisory lamp at B. Junction seized at both ends. The direction in which the seizure is to be effective depends on whether relay 10 or A6 operates first. If the operator at A is successful, 10 prevents the operation of 13 and the resulting calling signal WZ releases B3 which operates 53 to disconnect the operator at B who will receive busy tone. Relays 46,47 will have been energized but the sending out of a signal WY is prevented since relay 40 is shortcircuited by relay 50. This relay is subsequently rendered ineffective by relay 51. If A6 pulls up first the operator at B is successful, the operator at A being cut off by relay 13. Preventing simultaneous transmission of signals in opposite directions. Premature release. Any signal from A to B operates B4 which prevents 45 from changing its condition so that signalling from B to A cannot take place. Similarly, any signal from B to A operates A1 which prevents 21 from changing its condition. The release signal is, however, sufficiently long to override any other signal and consequently release of apparatus at one exchange when the operator at the other exchange releases prematurely, is ensured. Repeating coils A9, B9 for voice frequency currents. The coil A9 is designed to reduce the sensitivity of the alternating current relays AAW .. ADZ to currents coming from exchange A and to compensate for changes of impedance in the terminal circuit at A due to change over from the operator's circuit to the repeater AAE.