GB1257058A - - Google Patents

Abstract

1,257,058. Repeater testing. INTERNATIONAL BUSINESS MACHINES CORP. 16 Jan., 1969 [19 Jan., 1968], No. 2602/69. Heading H4R. In a four wire transmission system in which the repeaters RE and RR Fig. 2 are powered over the line via the go and return phantom paths, switches S1 and S2 are provided to loop back the output of the go repeater to the input of the return repeater for D.C. power and signal currents respectively. The switches are controlled, by circuit 15, so that they are closed when power is first applied to a repeater, preventing power being applied to a subsequent repeater, but are opened when the power current is interrupted for a predetermined short period, allowing power to be applied to the next subsequent repeater. During the time the repeater is looped back tests may be carried out on the signal loop. To establish which repeater is being tested pulses are transmitted from the terminal and the time between transmission and return is measured. Fig. 5 shows the control circuit in which power to feed the repeater is developed across Zener diodes Z1 and Z2 and this voltage is also applied via diode D4 to capacitor C1. When the supply has interrupted for more than a predetermined period of time capacitor C1 will be discharged and. when the supply is connected transistor T will initially not conduct, transistor T2 will conduct, SCR1 will fire and loop back the D.C. supply current from M2 on transformer TE2 to P2 on transformer TR2, preventing power being applied to the succeeding repeaters . Transistor T2, being conductive, will, via diode D3, hold transistor T1 non-conductive but capacitor C1 will charge up through diode D4 and resistor R6. In addition transistor T2, via diode D6, will hold transistor T3 non-conducting and will therefore allow signal to pass unattenuated from terminal 20 of the outgoing line via transistors T4 and T5 to terminal 19 of the return line, looping back the signal path. If the supply is interrupted for a time which is less than the discharge time of capacitor C1 then on reconnection transistor T1 will start to take current, due to its positive base bias from C1, T2 will therefore be cut off and SCR1 will remain non-conductive removing the loop back from the power supply feed. In addition the positive voltage on the anode of diode DC will cause transistor T3 to conduct, shunting the collector circuit of transistor T4 and preventing signal loop back from the outgoing amplifier terminal 20 to the incoming amplifier terminal 19. Power supply and signal voltages are therefore fed on to the next repeater in the transmission line. A circuit is described, Fig. 6 (not shown) for supplying a number of interruptions of the power supply to the line during a predetermined interval to enable the automatic switching on of all the repeaters when testing is not required. Also described are arrangements Fig. 7a and 7b (not shown) for determining the repeater-being looped back by feeding a signal to the outgoing line and time the interval before its return either by a counter or a voltage integrator.