GB651520A - Improvements in or relating to signalling systems - Google Patents

Abstract

651,520. Secret transmission. WESTERN ELECTRIC CO., Inc. Jan. 16, 1948, No. 1396. Convention date, June 19, 1946. [Class 40 (iv)] In a signal transmission system the instantaneous amplitude of a complex wave is continuously transmitted as a plurality of signal voltages of fixed magnitude each of which represents a different portion of the maximum signal amplitude and the portions are related in the binary scale. The signal from a microphone 10 after amplification in equipment 12 is applied to selective relays 14, 16 . . . 24, which unoperated have no output but in response to signals of more than a predetermined value produce at each of their output terminals a potential of that same predetermined value. The operating or output potentials of the selective relays 14-24 are related according to the binary scale and since the lower terminals of the relays 16-24 are connected to the output from the preceding relay the plurality of output potentials are always representative of the instantaneous signal amplitude. A diode 94, Fig. 2, is rendered conductive if the applied signal strength exceeds the opposing potential of a battery 98 so that the P.D. across the resistance 100 is increased and the anode potential of triode 104 is raised. The anode potential is limited to the required value (82 volts for relay 14) by diode 116 in conjunction with a battery 112 and is maintained at a predetermined potential (50 volts) in the absence of an operating signal by a diode 114 the anode of which is connected to a 50 volt tap on the battery 112. The selective relays 16, 18-24 function in an identical manner but the potentials of the incorporated batteries are different so that voltages of 16, 8, 4, 2 and 1 are produced. Since the voltage outputs 16, 8, &c. are relative to the outputs of the preceding stage it is necessary to incorporate a " digit grounder " circuit 26-36 in each relay which causes a predetermined voltage with respect to earth to appear at the output terminal of each operated relay irrespective of which of the preceding selective relays are functioning. The outputs from the associated relay 16 and the preceding relay 14 are connected to the grids of pentodes 136 and 138 respectively and the potentials with respect to earth of the upper ends of resistors 156 and 140 are averaged by a centre tap 50 of a high resistance potentiometer comprising resistor 148 and 162 to produce a potential of 8 volts at terminals 40. Potentials of 4, 2, 1, and ¢ volts are produced at terminals 42, 44, 46 and 48 respectively, by the operation of the relay, which may be transmitted by line or radio to D.C. amplifier limiters 50-60 each of which in response to a signal produces an output of 32 volts. Attenuators 64, 68-80, produce outputs related in the binary scale which are continuously added across load resistor 63 to reconstruct continuously the complex wave. Reference is made to the system described in Specification 630,094.