Patent GB-541373-A (GB)
Title: Improvements in or relating to carrier wave signalling systems
IPC: H04B1/74
Filed: 1940-05-23
Abstract: 541,373. Carrier repeating systems. STANDARD TELEPHONES & CABLES, Ltd., WRIGHT, F. C., and ALDRICK, S. E. May 23, 1940, No. 9121. [Class 40 (iv)] In a carrier system, failure to receive pilot current at an unattended repeater causes the substitution of a spare line and a subsequent failure of pilot current causes the original line to be restored. Three arrangements are described. The pilot current may be that used for automatic level control. In the arrangement shown in Figs. 1 .. 4, with pilot current coming in over the normal circuit in both directions, relays PA, PB are energized and CN holds PCN which controls the supply of power to the normal repeaters. If pilot current fails on either side, PA or PB energizes DS which starts a timing device, e.g. releases a sluggish relay DF. In due course relay CS is operated and causes power to be supplied to the spare repeater. DS is thus released, energizing DF, whereupon CB is energized and is followed by CBR. CN remains locked as well as CS. When PC, PD pull up in response to pilot current over the spare circuit, DS releases DF again to unlock CS, CN, the former remaining held however by PC, PD. CN in falling releases CB, whereupon DS falls, DF re-operates and CBR falls. Converse operations take place when the spare fails. In another arrangement, Figs. 5 to 7, the same repeater is used with spare and normal lines and if the pilot fails on one side only, only that side has the spare circuit substituted. In this case the failure of pilot current received from A and the consequent relapse of A energizes DSA to start a timing arrangement, e.g. to release DFA which in due course energizes PA. The delay is progressively larger in successive repeaters to ensure that change over only takes place at the first repeater to fail to receive pilot current. The others are held by pilot current sent from a source POA. DFA in falling also operates COA to connect up the spare line. On the reception of pilot current from the spare line, A re-operates and DSA falls re-energizing DFA to release PA. The local pilot source is thus disconnected. COC is re-operated but COA remains locked. When the pilot over the spare circuit fails, A releases DFA as before and PA operates. COA is released and the normal line' is re-connected. When the pilot is received over the latter, A and DFA pull up and COC is released. The circuit acts in the same way in the other direction. In a further modification, Figs. 8 to 10 (not shown), a change to the spare line is effected at all the repeaters in the system when the pilot current fails. In another arrangement, Figs. 11 to 15, failure of the pilot to reach the output of the repeater causes a local pilot generator to be connected to the outgoing line and a spare amplifier to be substituted for the normal one. If pilot current then reaches the responsive relay, the local source is cut out and, if a subsequent failure occurs, a spare line is connected up. A subsequent failure restores the normal line. If however the substitution of the spare amplifier does not clear the fault, the normal amplifier is re-connected before the spare line is substituted. In this case a subsequent failure causes the connection of the spare amplifier and the normal line is only restored if this expedient is unsuccessful. As there is only one spare amplifier for both directions, the first failure of the pilot from the other direction after the spare amplifier has already been cut in causes the spare line to be connected up but two spare amplifiers may be provided. Alarm signals.-Preferably arrangements are made to transmit to the attended station or to a suitable relay point by means of characteristic numbers of impulses over a separate circuit the following alarms and signals : (a) batterycharging set failure, (b) blown fuse, (c) start and finish of operation of battery charging set, (d) pilot failure, (e) repeater failure, (f) fire, (g) open door.