| 摘要 |
<p>1,021,418. Supervising unattended repeaters. STANDARD TELEPHONES & CABLES Ltd. Nov. 9, 1964, No. 45544/64. Heading H4R. In a supervisory system for two-way repeaters using different frequency bands for the two directions of transmission and in which repeater testing is carried out using two frequencies, or one frequency and the noise generated in the repeater, lying in the frequency band for one direction of transmission which, when modulated together, produce a difference frequency which lies in the frequency band for the other direction of transmission, the modulating circuit, units 10 to 13, Fig. 1, is connected, on the side of the repeater remote from the testing terminal station, between a pair of branching circuits so that the modulating circuit is isolated from W to E transmissions and faults in the modulating circuit have no effect on transmissions in either direction. Test signal transmission takes place via line 16, hybrid 9, line 14, hybrid 8, line 15, filter 10, amplifier 11, modulator 12, filter 13, hybrid 9, line 16 &c. The hybrid circuits 8 and 9 may comprise bridged-T networks as shown at 17 and 18, Fig. 3, the resonant circuits 20 and 21 being tuned to the test signal frequencies so as to block their transmission over the circuit W to terminals 26 but accept transmission from terminals 26 to the modulator circuit 19. The network 18 is arranged to provide frequency equalization which may replace that normally provided in the repeater. An equivalent form of the networks 17 and 18 is described with reference to Fig. 5 (not shown), this network having only one transformer 27 coupling the line to both input and output of modulator circuit 19.</p> |
