Patent GB-338972-A (GB)
Title: Improvements in or relating to telephonic and like signal transmission systems
IPC: H04B3/20
Filed: 1929-08-29
Abstract: 338,972. Electrical Research Products, Inc., (Assignees of Mathes, R. C.). June 11, 1929, [Convention date]. Repeating and amplifying systems.-In a two-way transmission system, including a very long line or a line of very high attenuation, speech currents at the terminal repeater station cause a courier impulse of alternating current to be sent over the line to condition the repeaters for the transmission of speech currents in that direction, and the speech currents are delayed for a time sufficient to enable the control to be effected at the distant terminal station before they are actually applied to the line. The necessary circuit changes are then maintained by the speech currents themselves. Fig. 2 shows an East terminal repeater station in which the transmitting path TA is normally disabled and the receiving path RA is normally operative, while Fig. 3 shows an intermediate repeater station in which both paths EA, WA are normally disabled. An alternative form of terminal repeater station is also described in which the transmitting path is normally operative and the. receiving path is normally disabled. A distinctive courier frequency outside the speech band is allotted for each direction of transmission. Assuming East to West transmission, speech currents arriving over the line TL control through an amplifier rectifier 38 a relav 39 which completes the transmitting path TA and two relays 40, 41, fastoperating and slow-operating respectively, which cause an impulse of frequency f2 to be sent out over the line TC from a generator 43 by way of a filter circuit 55 and an amplifier 56. The speech path TA includes a delay circuit 30 which imposes a delay t sufficient for the operation of the relay 39, a delay circuit 31 which imposes a delay T equal to the total transmission time of the line TC and a band-pass filter 32. A portion of the courier current, and after a time t a portion of the speech currents, pass into an amplifier rectifier 47 to control a relay 48 which disables the receiving path RA. At the intermediate repeater station, the incoming courier current from the section TC2 passes through filter circuits 60, 73 and then divides, a portion passing to the section TC1 through a filter 74 and an amplifier 75 and the remaining portion operating relays 66, 72, 83, through a delay circuit 80 and an amplifier repeater 81 to complete the speech path WA, further disable the other speech path EA and open the control circuit for West to East transmission. The delay circuits SO, 85 are designed to compensate for the unequal transmission times of the sections TC1, TC2; if these times are T1, T2. the former being the greater, the circuit 85 may be eliminated if the circuit 80 produces a delay T1-T2. Considering now the East terminal station for West to East transmission, the incoming courier current of frequency f, operatesrelays 51, 52, 53 through an amplifier rectifier 50 to disable the transmitting path TA and the control circuit associated therewith, this condition being maintained by the succeeding incoming speech currents. Specifications 142,115, 206,715, and 338,971 are referred to.