Patent GB-338971-A (GB)
Title: Improvements in or relating to telephonic and like signal transmission systems
IPC: H04B3/20
Filed: 1929-08-29
Abstract: 338,971. Electrical Research Products, Inc., (Assignees of Malhes, R. C.). June 11, 1929, [Convention date]. Repeating and amplifying systems.-In a two-way transmission system including a line of high attenuation such as a submarine cable, 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 in that direction, the speech currents being delayed so that they cannot arrive before the completion of the necessary circuit changes, which are thereafter maintained by the speech currents themselves. Fig. 2 shows an east terminal repeater station in which the transmitting path TA is normally operative and the receiving path RA is normally disabled, while Fig. 3 shows an intermediate repeater station in which both paths EA, WA are 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 11 a fast.-operating relay 12 and a slow-operating relay 13, which cause an impulse of frequency f, to be sent out over the line TC from a generator 14. The main speech path TA includes a delay circuit 6 which imposes a delay t sufficient to ensure that the circuit changes at each repeater station are completed before the speech currents arrive. A portion of the. courier current is diverted through a delay circuit 19 imposing a delay T-t, where T is the total transmission time of the line, to an amplifier rectifier 20 controlling a relay 21, which opens the circuit which receives incoming courier current from the West terminal station. This condition is maintained by the speech currents after a time t. Mechanical delay devices may be used in place of the delay circuits 6, 19. At the intermediate repeater station the incoming courier current from the section TC2 passes through a delay circuit 51 and then divides, a portion operating relays 44, 50, 58 through an amplifier rectifier 61 to complete the speech path WA and to open the control circuit for West to East transmission, and the remaining portion passing to the section TC1 through a filter circuit 52. This condition of the repeater is maintained by the speech currents which arrive after a time t. The path CA is common to both speech paths EA, WA and includes a band-pass filter 39 and a delay circuit 40. The delay circuits 51, 53 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 53 may be eliminated if the circuit 51 produces a delay T1-T2. The delay circuit 40 imposes a delay T1 sufficient to allow any speech energy ou the section TC1 to be discharged after the courier current reaches the West terminal station. Considering now the East terminal station for West to East transmission, the incoming courier current of frequency f1 passes through a filter circuit 25 to an amplifier rectifier 26 controlling relays 27 - - 30, which disable the transmitting path TA, close the receiving path RA and connect the amplifier rectifier 26 to a band-pass filter 24 to enable the condition to be maintained by the succeeding incoming speech currents. The receiving path RA includes a band-pass filter 8. Specifications 142,115, 206,715 and 338,972 are referred to.