SPECICATION NO. ETI/PSI/144 (12/91) SPECIFICATION FOR ... - rdso

(ii) Between pairs (adjacent quads) Less than 40pF Quads)
(g) Characteristic impedance of 1120 ohms
Paper insulated pairs at 300Hz
when loaded
(h) Insulation resistance when Not less than 10,000
measured at 500V meg. Ohms/km
(i) Loading at intervals of 33 milli Henries
1.33km
(j) Attenuation at 800Hz 0.25dB/km
when loaded
5.8.3 The characteristics of tapping, terminating and sectionalisting transformer
for voice frequency circuits are as under:
(a) Impedance ratio 1120:1120+2%
(b) Insertion loss from 300Hz Less than 0.9 dB
to 2500Hz
(c) Bridging loss with secondary Less than 0.015dB
open from 300Hz to 2500Hz
(d) Attenuation distortion from Less than +0.1dB
300Hz to 2500Hz
(e) Dielectric strength 2000V ac (rms) for
1 Minute
(f) Return loss in frequency More than 20 dB
range of 300 Hz to 2500 Hz
5.8.4 Isolating transformers will be installed at every 10 to 20 kms by the railways
to limit the induced voltage.
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5.8.5. Voice frequency repeaters will be provided by the Railways at intervals of
40 to 50 km to boost the signal level. The amplifier gain at the repeater station will be
about 20dB with an equaliser incorporated to compensate up to 0.02dB/kc/km. The
SCADA equipment shall, however, incorporate an amplifier having a minimum gain of
30 dB to compensate for any signal level variation at difficult points in the system.
5.8.6. The repeater section far and cross talk attenuation (equal level cross talk)
between any two voice frequency pairs at a frequency of 800Hz will be not less than
65dB and that at the near-end not less than 61dB.
5.8.7. The underground trunk cable being normally laid close to the railway track,
the lead from tapping transformers to the remote control or control building would be
small.