Patent GB-1497740-A (GB)
Title: Device for enabling the telemonitoring of high-frequency pulse regenerative repeaters in a transmission line
IPC: H04B17/40
Filed: 1975-06-27
Abstract: 1497740 Testing regenerative pulse repeaters COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS CIT-ALCATEL 27 June 1975 [28 June 1974] 27394/75 Heading H4L Apparatus for telemonitoring a series of M regenerative repeaters in a transmission line, comprises at each repeater station, Fig. 1, an error counter 6 feeding a p-bit error rate coder 7 and means for inserting the coded rate into a respective one of M channels of a frame having at least pM slots. The clock signals H, Fig. 3, of frequency f, e.g. 30 Hz, modulate a carrier of frequency F, e.g. 500 Hz. A frame begins with a frame synchronizing word VT which is followed by channels R 1 , R 2  &c. containing the error rate coding of the 1st, 2nd &c. repeaters in the line, the number of errors being counted during a given time less than the duration of a frame. An element 2, Fig. 1, at the input from line L 1  separates the modulated carrier Ffrom the signal, which may be digital data, via terminal S,. Element 2 may be a network comprising transformer windings (51-55) and capacitors (35,36), Fig. 5 (not shown). A low frequency detector 4 separates the modulation which is stored in a shift register 8, clock pulses for the latter being provided by a clock restoring circuit 9. The contents of the shift register 8 is passed to the output line L 4  through a gate 13 leading to an error rate modulator 14 which co-operates with a carrier restoring circuit 17 to regenerate the required monitoring signal output. The output of the shift register 8 also feeds a synchronizing word decoder 10 which detects the frame synchronizing word VT and resets to zero a modulo p counter 11 which delivers to a channel decoder 12 a pulse at every p pulses of the clock signal H, corresponding to each channel R 1 , R 2  &c. When a free channel is detected by channel decoder 12 it controls gate 13 to admit the error rate count from coder 7 to modulator 14. If the repeater station preceding that shown in Fig. I is defective in so far as it does not retransmit the monitoring signal, the absence of the latter actuates a long absence detector 15 which turns switches a and b to the a2, b2 states, thereby connecting to the input of 4 units comprising a generator 16 for the frequency F, a frame synchronizing word generator 19 and a frame synchronizing modulator 18. Thus the monitoring signal is regenerated at the first repeater following a defective repeater. If the defect is such that a signal of frequency F is passed but the monitoring data are erroneous, e.g. as regards the frame synchronizing word or the coder 7 output, a control device 56 opens a switch 57, a new monitoring signal being generated by the next repeater in the series. A receiver for the monitoring signal at the live terminal comprises a low frequency detector (4), Fig. 2 (not shown), a clock restoring circuit (9), a shift register (8), a decoder (10) and modulo p counter (11) as in Fig. 1. The output of the counter (11) is connected to a channel counter (21) for counting the number of channels in a frame. The output passes to addressing circuits (22) for decoders (23) and display units (24) comprising one for each repeater in the series. The gate 13 may comprise two AND gates (26, 27), Fig. 4 (not shown), an inverter (25) and an OR gate (28). The long absence detector 15 may comprise a transistor (39), Fig. 6 (not shown), having its base connected to terminal S 1 , Fig. 1, and having its collector connected to a parallel RC circuit (37, 38) with a time constant of the order of 10 sec. An error detector 5, Fig. 1, which feeds the error counter 6 may comprise, in the case of a bipolar code, three flip-flops (46, 46, 47), Fig. 7 (not shown), and comparators for positive pulses (48) and for negative pulses (49) feeding an OR gate (50).