| 摘要 |
1319062 Testing unattended repeaters HASLER AG 17 July 1970 [23 July 1969] 34895/70 Heading H4R In a system for the remote testing of a repeater in a pcm transmission line, in which repeater power is supplied over the line, a resistor 6 is connected in series with the power feed to the repeater amplifier with a switching device 7, connected in parallel with the resistor and operated to open circuit the parallel path on reception of a specific pattern of impulses detected. Two different patterns of impulses are transmitted during testing, one of which operates the switching circuit and the other of which does not, but both have the same effect as far as amplifier loading is concerned, making resistance measurement of the D.C. feed path, to determine the location of a fault, more accurate. As described a test transmitter produces two sequences of impulses, e.g. 010101 ... or 0000111100001111 ... and the transmitter switches between these impulse sequences at either a 1 KHz or 2 KHz. The repeater ineludes a resonant circuit 8 tuned to 320 KHz which is the resulting frequency of the second impulse sequence 0000111100001111 .... The signal developed across the resonant circuit, which will be 320 KHz modulated by either 1 KHz or 2 KHz is fed, via amplifier 9, to rectifier 10 and band-pass filter 11 which passes 1 KHz. The output from the filter is arranged to operate a Schmitt trigger 13 to make transistor 7 non-conductive only if there is a 1 KHz signal present at the output of filter 11. The system maybe adapted to operate with separate repeaters for each direction of transmission, which are fed in parallel, by making the 1 KHz detector circuit responsive to 320 KHz signals in either the forward or return signal channel, Fig. 2 (not shown), or by having respective detectors and switching devices operating on a common feed resistor. |
