GB596676A - Improvements in or relating to electric pulse signalling systems - Google Patents

Abstract

596,676. Multiplex pulse signalling. STANDARD TELEPHONES & CABLES, Ltd., CHATTERJEA, P. K., and AMBROSE, D. M. May 12, 1945, No. 11987. [Class 40 (v)] Calling, dialling, supervisory &c. signals are transmitted in a pulse communication system by time modulating the pulses with a periodic wave having a frequency related to the pulse recurrence frequency by a ratio expressible by small integers and of phase related in definite manner to that of the pulse train. As described, a multichannel transmitter, Fig. 1, comprises a master saw-tooth generator 1, with a repetition frequency of 10,000 c.p.s., which is connected to four channel pulse generators and pulse-phase modulators 2 ... 5 and a synchronizing pulse generator 6. The pulse outputs are mixed, amplified and shaped in unit 7 and applied to the communication medium 8. Modulating signals such as speech are applied from terminals 9... 12 through switches 13 ... 16 respectively to the modulators 2 ... 5 respectively which may be of the type described in Specification 596,658. The master generator 1 is also connected to a frequency divider 17 with an output of 5000 c.p.s. which is passed through low-pass filter 18, the sine wave output of which is fed through a phasing network 19 to the lower contacts of switches 13 ... 16. Operation of these switches to their lower contacts for calling purposes disconnects the corresponding signal source 9, 10, 11 or 12 and substitutes the 5000 c.p.s. sine wave from unit 19. At the receiver, Fig. 2 (not shown), a low-pass filter following the demodulator rejects the calling frequency and passes the speech while a band-pass filter and a tuned detector operate a relay and bell or other signal when the calling frequency is received. Alternatively and preferably the calling frequency wave is of rectangular form and its requirements as to frequency and phase are discussed in the Specification. In some systems it is preferred to provide individual phasing networks such as 19 for each channel.