Patent GB-173284-A (GB)
Title: Ringing arrangement for carrier wave signalling system
IPC: H04J1/14
Filed: 1920-09-16
Abstract: 173,284. Western Electric Co., Ltd., (Western Electric Co., Inc.). Sept. 16, 1920. Manual exchange systems and apparatus; repeating and amplifying systems.-Relates to means for transmitting call, supervisory or like signals in a multiplex system, in which a number of ordinary telephone lines are associated with a common high-frequency line, between two stations, each ordinary line at one station being assigned a carrier frequency for communication with a corresponding line at the other station. Relays are so arranged that ringing current from any ordinary line cuts out the associated speaking circuits, and low-frequency ringing current in the ordinary lines is translated into modulation of somewhat higher frequency in the high-frequency line, and vice versa. The common highfrequency line ML is coupled to a series of receiving sets at RF1, RF2, &c., each set having a distinctive carrier frequency, and to a series of corresponding transmitting sets at TF1, TF2, &c. a bridge with artificial line MN being provided to prevent interference between the reception and transmission of carrier waves. A bridge with artificial line N1 fulfils a similar function for low frequency currents over the ordinary line L1. Outgoing speaking current from the line L1 passes via the circuit TL, to the modulator M1, which is preferably of the kind described in Specification 130,219, [Class 40 (v), Wireless signalling &c.]. High frequency current is supplied from the circuit 12, and carrier-waves are only transmitted during actual modulation. The filter TF, preferably of the kind described in Specification 142,115, is designed to pass a band of frequencies lying in the neighbourhood of the assigned carrier-frequency. An amplifier TA1 preferably of the duplex type, and a second filter TF1, are provided. Inc ming speech-modulated carrier waves of the appropriate frequency from the line ML pass through the filter RF, and a demodulator D, which is preferably of the kind described in Specification 130,432, [Class 40 (v), Wireless signalling &c.], and is supplied with high-frequency oscillations from the local circuit 13'. The demodulated or speaking current passes to the line L, by way of the amplifier RA1 and filter RF1<SP>1>, the latter being adapted to pass all voice frequencies. Outgoing ringing current of, say, 16 cycles per second from the line L, is translated into a modulating current of, say, 133 cycles by the action of the ringing-responsive relay 13, which by de-energizing the slow-acting relay 14 energizes the relay 15 and so cuts in a ringing source RS, which may be of the type shown in Fig. 2, and is common to all lines such as L1. At the same time the 133-cycle current is excluded from the line L1 by the breaking of contact at 31, 32 and false operation of the relays 17 and 19, 20, is prevented by the breaking of contact at 33 and at 34. Incoming ringing-oscillations from the line ML modulated at 133 cycles actuate the tuned relay 17, a 133-cycle rejector circuit 21, 22, 23 being provided in shunt. The relay 17 by de-energizing the slow-acting relay 18 energizes the relays 19, 24, of which the former connects the line L1 to a ringing source at 16 cycles while the latter, by energizing the relay 20, short-circuits the transmitting-transformer 11 and cuts out the relay 13 to prevent its being falsely operated. The relay 24 is of the slow-release type in order to prevent false actuation of the relay 13 by capacity discharge from the line.