GB1038672A - Improvements in electrical signalling systems - Google Patents

Abstract

1,038,672. Testing repeaters. BRITISH TELECOMMUNICATIONS RESEARCH Ltd. May 11, 1964 [May 15, 1963], No. 19344/63. Headings H4L and H4R. In a signalling system, Fig. 2, which is particularly suitable for pulse transmission, having separate send and receive paths employing a plurality of repeating stations SRI to SRN and RRI to RRN, which are fed with D.C. power in series from a terminal station T, when the system is not energized the send and receive paths are connected together at each repeater station by relay contacts AL, and each repeater station includes a device responsive to a momentary increase in feed current whereby the connection between the send and receive paths at the corresponding repeater station is broken and power is supplied to the succeeding repeater station. At the terminal station T a rotary switch S connects up in turn Zener diodes MR21 to MR25 as voltage limiters and in each position a switch MS is operated to connect timing equipment MS to control the constant current generator CG to increase the feed current for a short time to energize the corresponding repeater station. The Zener diodes may be replaced by a chain of diodes with the switch S connecting in turn to different junctions in the diode chain. During the operation of energizing the repeater stations a test signal is applied to the send path which will be returned to the terminal station via the successive loops, the receiver operating an alarm if the response is unsatisfactory. Alternate repeater stations may be arranged to switch automatically a predetermined time after current is supplied to them. In a repeater station, Fig. 1 (not shown), the sending repeater is powered from across the Zener diodes MR1 ... MRX and the series circuit from the terminal station initially also includes resistor RI, the receive repeater being similarly connected across Zener diodes in the return line. When the station is powered initially the voltage drop across resistor RI and diodes MR1 ... MRX is less than the Zener voltages of Zener diodes MR11 and MR12 so that diode MR10 is back-biased and insufficient current flows to operate relay AL. If a small increase in the feed current is made, diodes MR11, MR12 will conduct and relay AL will operate to disconnect the shunt across the signalling paths and to apply a potential via resistor R2 so that transistor VT conducts. Nearly all the feed current now flows through transistor VT and maintains relay AL operated, and diode MR10 is conductive so as to pass most of the current for operating the repeater. When the feed current is reduced to its normal value the relay AL will remain operated to permit power to be extended to the next station.