GB762915A - Carrier communication system - Google Patents

Abstract

762,915. Multiplex systems. AUTOMATIC ELECTRIC LABORATORIES, Inc. Sept. 13, 1954 [Sept. 28, 1953], No. 26457/54. Class 40 (4). In a carrier current communication system for the transmission of signals in a plurality of contiguous channels of the same nominal width, one more carrier frequency than the number of channels is provided and a switching arrangement connects to the respective modulator and carrier frequency which is optionally either the one at the low frequency or the high frequency end of each channel filter. The audio " tail " in the system shown may be " four-wire" across terminals 3 and 5 or " two-wire " on terminals 5 and in the latter case a resistance hybrid 9 is brought into circuit. Low-pass filters 13 and 15 for the two directions and a V.F. or pilot filter 17 passing 3400-3550 cycles for signalling purposes are assembled in a plug in unit 19 which is identical for all channels. The modulator 21 and demodulator 41 of channel 1 may be fed by either an 8 or 12 Kc/s. carrier and the leads 23 are terminated on jacks 211M and 211D, Fig. 3, respectively. Carrier frequencies 8, 12-24 Kc/s. are also terminated on the jacks and the channel-carrier frequency interconnections are determined by the jumping across the pins of plugs 216A and 216B. Thus, channel send filter 27 selects the upper sideband on the 8 Kc/s. carrier when plug " A " is used and the lower sideband on the 12 Kc/s. carrier when plug " B " is used. Signalling is effected over lead 33 via a signalling oscillator 35 and a modulator 37 and the V.F. signal is combined with the channel signal through a hybrid transformer 25. Groups of four channels are modulated on a 96 Kc/s. carrier in pre-group units and an annulling unit 66 is provided to sharpen the filter cut-offs at the extremities. The combined pre-group unit outputs, after amplification, pass through an E-W station switch which inserts a modulator 99 in the " go " or " return " path in accordance with predetermined setting up arrangements. Pilot signals for automatic gain control and frequency correction are provided by oscillators 110, 112 and the signal passes to line via one of the directional filters 121, 115. Flat gain and slope control are effected in the system regulating unit and further regulation is effected by the V.F. signalling current in regulator 39. The V.F. signals which are selected by a filter 17 and amplified also energize a receive relay 55 to repeat the supervisory signals to the local switchboard over lead 57. All the frequencies required are derived from the outputs of crystal oscillators 165, 169, which are housed in an oven 163.