Patent GB-396116-A (GB)
Title: Improvements in or relating to electric signalling systems
IPC: H04B3/20
Filed: 1932-02-03
Abstract: 396,116. Two-waytransmission. ELECTRICAL RESEARCH PRODUCTS, Inc., 195, Broadway, New York, U.S.A.- (Assignees of Horton, A. W. ; 160, Prospect Street, East Orange, New Jersey, U.S.A.) Feb. 3, 1932, No. 3251. Convention date, Feb. 11, 1931. [Class 40 (iv).] In a two-way system having directional switching apparatus, noise incoming from a transmission line is attenuated except when speech comes over the line, the noise attenuator being disabled by such speech currents. The noise attenuators may also serve to reduce clicks due to switching, and noise-echoes. In the system shown in Figs. 1 and 2, a station A is connected by transmitting and receiving circuits TC, RC, to a station B at the terminal of cable CL. At station A, switches 100, 101 which may be controlled by relays or plugs and jacks, connect the circuits to lines L1, L2 or by a hybrid coil to a two-way line LL, pads 104, 105 being included in the hybrid coil circuits to reduce the energy level since high levels produce singing. A noise attenuator 89, 90 is inserted in the receiving circuit at stations A or B or both. The transmitting circuit is normally disabled at contacts of relays 22, 30 at stations A and B, while the receiving path is, including the attenuators, normally operative. Speech currents over TC pass volume control 10 to a conditioning circuit comprising delay circuit 11, rectifier AD and relay 22, relay 58 being also operated to disable the receiving path. At station B, the speech currents find amplifiers 14, 15 paralysed by grid-bias battery 23, but a by-pass over 66 operates amplifier 65 and rectifiers 67, 52 of which 67 counteracts the bias of battery 23 and 51 applies a paralysing grid bias to amplifiers 38, 39 in the receiving path. Anode current from battery 83 over relay 70 commences to flow in amplifiers 14, 15, the relay pulls up and removes the shortcircuit around relays 30, 48, 71 of which 30 completes the transmitting path, 48 opens a first point in the receiving path and 71, after a delay, operates 49 and 50 to open further points in the receiving path. When speech over TC ceases, the circuits at station A restore in the ordinary way, paralysing bias is again applied to amplifiers 14, 15 so that anode current ceases and relay 70 restores slowly to permit complete passage of speech. Relays 30, 48 fall back and 71 slowly releases to permit dissipation of cable discharge over contacts of 48 into equalizer 35 before relays 49 and 50 complete the receiving circuit. On receipt of speech from the cable, rectifier 93 operates relay 91 to remove the noise attenuator 89, and rectifier 69 disables amplifier 65 to prevent operation of the control devices 67, 52 from the transmitting path. At station A, rectifier 62 operates relay 63 to prevent operation of disabling relay 58, and rectifier 61 operates relay 92 to remove noise-attenuator 90. In the symmetrical circuit shown in Fig. 3, a noise attenuator 113, 114 is inserted in each path. Speech from L3 to L4 operates relay 123 to prevent operation of path-disabling relay 121 and attenuator-disabling relay 115 by speech in the opposite direction. Relays 116 and 122 are operated to disable the attenuator in the speaking path and disable the other path respectively. Simultaneous speech in both directions operates relays 123, 124 and the attenuators are not disabled but attenuate the echo. Direct speech is also attenuated and will cause the speaking parties to pause.