GB676792A - Carrier current signalling system - Google Patents

Abstract

676,792. Two-way transmission. DEHN, S. G. (Automatic Electric Laboratories, Inc.). Sept. 13, 1949, No. 23615/49. Class 40 (iv). In a carrier current communication system in which the carrier is used for signalling, a relay 4 for imposing ringing current on a voice frequency line 1, 3 is controlled by the potential across a sharply-tuned resonant circuit. In the embodiment shown, incoming carrier frequency currents from line 41 are applied to the resonant circuit comprising an inductance 85 and condensers 81 and 83 via a high-pass filter 37, lines 43 and 71, transformer 75 and line 35. The potentials across the tuned circuit control a valve 89, the output of which is rectified and fed back to the grid via resistor 113 to reduce the anode current and release the relay 4, which connects a ringing source to the V.F. line and switches in a resistor 67 to maintain the balance of a hybrid transformer 9. Ringing currents from the V.F. line operate a relay 27 which provides a path between a modulator 15 and the line 41 and cuts out a tuned circuit 49 and 57 which normally serves to suppress the carrier. The two-way transmission of speech currents through the single modulator 15 is the same as is described in Specification 672,729.