Patent GB-738464-A (GB)
Title: Arrangement for supervising, remote-controlling, or locating faults in unattended intermediate amplifiers affected by transmission faults
IPC: H04B17/40
Filed: 1953-10-12
Abstract: 738,464. Two-way transmission. FELTEN & GUILLEAUME CARLSWERK AKT.-GES. Oct. 12, 1953 [Dec. 22, 1952], No. 27956/53. Class 40 (4). Intermediate unattended amplifying stations are controlled, supervised, and fault tested in turn by a signal transmitted from one end of a two-way transmission system, the signal being passed through all the filters in one transmission direction of a two-wire both-way repeater and through the common amplifier and, after frequency changing whereby it constitutes a return signal indicative of a successful test, through all the filters in the other transmission direction and again through the amplifier. In the arrangement described and shown in Fig. 1, frequency bands of 24-216 kc/s and 264-456 kc/s transmitted in the A-B and B-A directions are directed through a common amplifier V at a repeater by way of low and high-pass filters TP1, TP2 and HP1, HP2 respectively. Each direction of transmission is continuously monitored by pilot frequencies of 23 and 457 kc/s, and a failure or lowering in level of .one of these frequencies causes the emission of 20 and 220 kc/s signals and 260 and 480 kc/s signals in the A-B and B-A directions respectively. The 20 and 480 kc/s frequencies constitute the controlling &c. signals for the two directions while the 220 and 260 kc/s frequencies are testing signals which indicate to their respective transmitting terminal stations that a fault has been detected. If the B-A transmission is defective, the 20 and 220 kc/s frequencies are transmitted in the opposite direction. At the first repeater, the 20 kc/s signal is rejected from the transmission path by a band stop filter 8 after passing through TP1, V and TP2, and is applied over a contact pr2 and a band-pass filter 6 to a frequency doubler VD. The resulting 40 kc/s signal is modulated at M by the 220 kc/s signal supplied over a band-pass filter 4, and a sideband of 260 kc/s selected by a filter 2 constitutes a return signal which passes through HP1, V and HP2. Switch through to the next repeater is effected by a 21 kc/s signal transmitted from the terminal station. The signal produces a resultant frequency of 262 kc/s over the modulating circuit which constitutes both a return frequency and an operative frequency for a polarized relay PR which is pulled up over a band-pass filter 9 and a rectifier GL1. The band-stop filter 8 is then short-circuited and frequencies in the band 20-22 kc/s are permitted to pass to the next repeater, which is tested in like manner. If the repeater is initially connected for control and testing in the B-A direction by contacts pr1, pr2, the bandstop filter 8 is brought in circuit by transmitting a 218 kc/s signal which operates relay PR over a band-pass filter 10 and rectifier GL2. When testing takes place from the other end of the line, a band-stop filter 7 rejects the signal frequencies 478-480 kc/s which then pass over contact pr1 and a band-pass filter 5 to the modulator, the side bands 218-220 kc/s being selected by a band-pass filter 1. The arrangement for testing in the B-A direction is the same as that previously described except that different single frequencies are used and the frequency doubler is not required. If the filter 7 is initially short-circuited by pr1, then relay PR is changed over by a 262 kc/s preparatory signal. At a faulty repeater, changeover to a reserve amplifier may be effected by either reversing or reducing the direct current through the line. This changeover may be automatic if a valve heater fails. By transmitting frequencies of 21.5 kc/s and 479 kc/s in the A-B and B-A directions respectively which operate a relay PR<SP>1</SP> at each repeater over amplifier V and band-pass filters 12 and 11, amplifier changeover by direct current control is restricted to the faulty amplifier only. These frequencies are also applied over operated contact pr<SP>1</SP>1 to the modulating circuit in which they are combined with the continuously transmitted frequencies of 220 and 260 kc/s to produce return frequencies of 263 and 219 kc/s respectively, a band-pass filter 13 preventing frequency doubling of the 479 kc/s signal. In the amplifier heater circuits, Fig. 2, a condenser C and choke D isolate the direct current from the A.C. signals. When. a heater fails, the direct current in the line is maintained over gas tube GR, and a selector dw is stepped to the next heater circuit when a magnet DW is operated by current reversal in the line. This takes place only at the faulty station since the magnet is short circuited at all other stations by the operated contact pr<SP>1</SP>2. In an alternative arrangement, Fig. 3, the next heater circuit is brought into use automatically by operation of DW when the gas tube fires. In a further arrangement, Fig. 4, the choke D also constitutes a relay which falls back when the direct current is reduced and closes contact d. Magnet DW then pulls up provided relay PR<SP>1</SP> is not operated. With the gas tube in the position shown, automatic transfer to the next heater circuit is effected when a heater fails. This does not take place if the gas tube is connected in the position shown in dotted lines. To restore the operated PR<SP>1</SP> relays when amplifier changeover is completed, frequencies of 20.5 and 261 kc/s are transmitted by the terminal stations. In the B-A direction the latter frequency restores relay PR<SP>1</SP> directly over a band-pass filter 14. In the reverse direction the 20.5 kc/s frequency is applied to the modulator, and after combination with the continuous 220 kc/s signal produces a resultant frequency of 261 kc/s.