Patent GB-565639-A (GB)
Title: Improvements in telephone or like systems
IPC: H04Q3/00
Filed: 1943-05-15
Abstract: 565,639. Exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., GILLINGS. C., and BEALE, C. E. May 15, 1943, No. 7770. [Class 40 (iv)] In a system employing voice-frequency signalling between manual positions, all the signals after the seizure signal comprise a constant length prefix of combined frequencies followed by a suffix which is characteristic of the signal. The arrangement is suitable for working over an international trunk IT, Fig. 3a, between networks CCIF, BPO, one of which uses v.f. signalling involving combined frequency prefixes, while the other uses v.f. signalling with single frequencies only. The relay sets IRS, BRS1, BRS2, ORS associated with the v.f. receivers VFR1 ... 4 on either side of the positions IP1, IP2 are arranged to split the line whenever a supervisory signal is received in order to prevent interference between signals on the various line sections. The both-way relay set BRS1 or BRS2 shown in Figs. 1-4 is provided with outgoing and incoming jacks OGJ, ICJ and operates on a sleeve-controlled basis. Each signal is sent during a cycle of a rotary switch TS which may make several cycles when the signal is one that is repeated. The trunk normally terminates in a resistance pad YF ... YJ which is cut out by sleeve relay DR when a talking condition exists. When the trunk is seized, sleeve relay S connects up CX which starts the switch TS, and relay SS is operative in positions 1-5 to send a signal of frequency X. Relay CZ then pulls up, releasing CX, and the switch continues to its home position. At the incoming end, the responding relay XR connects up IR, which locks and lights the calling lamp ICL. When the call is answered, sleeve relay S connects up IS. Either operator can recall by means of her ringing key which brings up RR, thereby causing the switch TS to send a prefix comprising frequencies X and Y for 280 ms. followed after 30 ms. by a suffix of frequency X for 550 ms. Relay SS in this case is operative in positions 1-41, and high resistance relay SZ energizes in position 14 in series with the switch magnet and immediately short-circuits itself in order to provide the space between the prefix and suffix. At the receiving end where relays XR, YR respond to frequencies X, Y, the prefix energizes PS, which converts the line termination into one of infinite attenuation and holds until the arrival of the suffix, which energizes FR to light the supervisory lamp. The signal is repeated as long as the ringing key is actuated and the lamp therefore flashes. It should be noted that at the outgoing end SZ energizes momentarily in positions 46 and 48 of the switch TS and the interval between repetitions is 260 ms. This does not occur when the signal is sent from the incoming end since IS is up and the interval is therefore reduced to 200 ms. When either operator clears, the relapse of S, DR connects up RC to initiate a clearing signal which comprises the same prefix followed by a suffix of frequency Y for 70 ms. and is sent as before under the control of SS, SZ. The interval between repetitions is 740 ms. at the outgoing end and 680 ms. at the incoming end. At the receiving end, PS responds to the prefix as before and the suffix energizes YS, whereupon DC pulls up, locks and lights the supervisory lamp. When the other operator clears in response to this signal, RC energizes immediately YR falls back after the completion of a received signal and initiates an acknowledgment signal of similar character, which is not repeated, however, since SH, RC are released by FZ which pulls up on the relapse of SS and falls back releasing DC when TS reaches its home position. At the end from which the clearing signal is sent, the acknowledgment is received when TS is beyond position 18 and causes the operation of PS, YS, DC, FZ and the last relay disconnects SH, RC as soon as the signal is complete. A clearing signal before the call has been answered dims the calling lamp and is immediately acknowledged. The shorter interval between repetitions of the clearing signal from the incoming end ensures that should the operators clear simultaneously the second cycle from that end will be effective. The v.f. signals may modulate a carrier, in which case the trunk might involve either a wire or radio link.