Patent GB-530704-A (GB)
Title: Improvements in and relating to electrical communication systems employing wave repeaters
IPC: H04B3/20
Filed: 1939-06-17
Abstract: 530,704. Two-way transmission. STANDARD TELEPHONES & CABLES, Ltd., and FILBY, F. G. June 17, 1939, No. 17713. [Class 40 (iv)] In a system including lines for the transmission of broadcast programmes, direct current impulses are employed for the switching on and off of amplifiers at unattended repeater stations and for reversing the direction in which they are connected in the line. The impulses are sent from one terminal station and are repeated from each station to the next, and checking signals of the same nature as the control signals are sent back from each station. The other terminal station, if it contains no amplifier, may have apparatus for indicating the condition. The repeater stations are also arranged to send fault signals to the terminal station and at the same time switching-off signals to the more remote stations. The various signals may pass over a channel different from that to which they relate. Terminal station, Fig. 4. Assuming manual control, key FK is thrown to send the switching- on signal. Relays FB, T, TA, TB energize and relay FA releases slowly, whereupon T, TA, TB release slowly in succession. Relay SR energizes when FA is back, relapses when T is back, re-energizes when TA is back and falls back finally when TB is back, so that two spaced impulses are sent over the line L by way of a low-pass filter LPI, the purpose of which is to reduce noise. After an interval, a similar checking signal is received by relay CS from the first repeater station. Relay CB pulls up at the first operation of CS, CC at its release and CF at its second operation. The first impulse must not exceed the release time of CA, and the subsequent space must. not exceed the release time of CB. Further checking signals are received from other repeaters along the line, and a switch FS advances one step for each until, when all are received, relay FE energizes. The system is now conditioned for East to West transmission. To adjust for West to East transmission, key MRK is operated momentarily. Relay RT pulls up and then releases slowly, so that SR sends a long impulse during the release period. Alternatively, this action may be brought about automatically from a circuit ASC associated with the broadcast transmitting apparatus by the grounding of wire OC and operation of relay OL. In this case the circuit of RT is made momentarily until RC falls back by the operation of RA. The corresponding checking signals are long enough to release CA, and bring about the operation of CR. A switch RS advances one step for each signal until, when all are received, relay DI energizes. A further reversing signal may be sent in a similar manner, except that when initiated from the circuit ASC, the circuit of RT is made on the release of OL, RA. The checking signals then restore the switch RS to normal. To send the switching-off signal, key FK is restored, whereupon FA, T, TA, TB energize, FB releases and T, TA, TB release slowly in succession to send two spaced impulses as described above. The operation of FC restores the switch RS if necessary. The checking signals restore the switch FS to normal. Switching on may be effected from the circuit ASC by grounding of either of wires IC, OC to operate IL or OL, either of which connects up AF to perform the functions controlled by key FK. When switching on is complete and FE energizes, a circuit is made at once for RA if OL was the relay which operated originally, and the reversing signal is sent. The disconnection of AF by IL or OL effects switching off. In the event of a fault at a repeater station, a signal comprising two spaced impulses is received, and the switch FS advances one step, operating an alarm relay FF. The operator sends the switching-off signal, and since check signals will be received from all stations previous to the faulty station, it can be identified by watching the check signal lamp SL. Other lamps are provided to indicate the condition of the system. A disabling key may be provided in the wires IC, OC. Intermediate repeater station, Fig. 5. The switching - on signal is received by relay WA, and B pulls up at its first operation, C at its release, and FR at its second operation. The last relay switches on the filaments over wire FL, and when anode current flows relay P energizes over wire PL. Relays T, TA, TB energize and then release slowly in succession, controlling relays FS, BS to send two spaced impulses in both directions over the line L, that is, the switching on signal to the next repeater station and the checking signal to the terminal station. Relay PF then operates. Checking signals from subsequent repeater stations are repeated by EA, BS. The reversing signal, which is longer than the release period of A, brings about the operation of RS which releases slowly at the end of the signal, and a corresponding signal is sent in both directions by FS, BS. Relay LR energizes and reverses the connections of the amplifier IR4 to the line as indicated in Fig. 6. On a further reversal, SS energizes instead of RS and disconnects LR. The occurrence of a fault releases P, PF and PA, ER operate during the release time of PF, unlocking filament relay FR and controlling T, TA, TB to send two spaced impulses in both directions, that is, a switching- off signal to more remote stations on the line and a fault signal to the terminal station. An alarm relay MA also operates. The switching- off signal is the same as the switching-on signal, but since P is up, ER energizes in response and unlocks FR, which in turn unlocks LR if operated. On the relapse of P, ER falls back and a similar signal is sent in both directions by means of T, TA, TB as described above. The input of the repeater may be connected over a manual switch SI to a local studio line LO, Fig. 6, by operation of relay LL under control of key LLK. Similarly the output may be connected over manual switches S2, S3 to a monitoring line LO<SP>1</SP> and loudspeaker LS. Relay LL is disconnected by a reversing signal. The control from the terminal station is effective only when key MCK is in its lower position in which battery from wire RB is fed to all the relays except LR, LL, MA. For local control, key MCK occupies the position shown, and it may be moved to its upper position in order to operate LR. An incoming signal during a condition of local control merely operates alarm relay WA.