GB299916A - Improvements in telephone and like signalling systems - Google Patents

Abstract

299,916. Standard Telephones & Cables, Ltd., (Western Electric Co., Inc.). Aug. 5, 1927. Inverting and transposing frequencies of telephone currents; twoway repeating systems.-In a fourwire repeating circuit, a single oneway device such as a scrambler is connected up for transmission in both directions by speech-controlled relays. In the arrangement shown, speech incoming from the circuit 26 (connected for example to a radio receiver) passes through an amplifier to the scrambler 22 and thence through further amplifiers to the line L. A delay network 28 prevents the speech from reaching the hybrid coil until the echo suppressing relay 15 has pulled up. Singing of the radio side is prevented by the back contact of relay 30 and of the other side by that of relay 31. Speech in the other direction energizes relays 16, 30, 31, 32 and passes through the scrambler 22 and amplifier 23 to the circuit 25 connected for example to a radio transmitter. Delay networks 19, 100 prevent these currents from passing to circuit 9 before relay 16 pulls up, and relay 32 prevents the radio side from singing. Construction of scrambler. Speech incoming from 26 is divided by filters F<A> - - F<D> into sub-bands which are modulated to bring them to a common frequency level in modulators M<A> - - MD. The resulting subbands are then led through key switches which change the relative positions of the sub-bands in any desired manner to de-modulators DM<A> - - DM<D> which convert them into four sub-bands having the same frequency limits as the original sub-bands with or without inversion of the frequencies within the sub-band. It will be seen that these scrambled currents can be converted into intelligible speech by passing through a scrambler of identical construction but with the key switches set in a complementary manner as indicated by the dotted lines.