GB1029988A - Arrangement to improve the signal-to-noise ratio on line systems with high noise level - Google Patents

Abstract

1,029,988. Transmission systems. TELEFONAKTIEBOLAGET LM ERICSSON. Feb. 27, 1963 [Feb. 28, 1962], No. 7954/63. Heading H4R. In a power distribution network wherein tandem exchanges are associated with each transformer station and carrier-frequency signals are transmitted over the network and through one or more exchanges, each signal is accompanied by a pilot signal which adjusts the gain of an amplifier at each exchange through which the signal and the pilot passes. By the use of a single pilot signal inserted at the transmitting station it is stated that the signal-tonoise ratio is considerably improved over the more usual systems in which a fresh pilot is injected at each tandem exchange. A subscriber 9 is connected through a local exchange 8 to a 4-wire tandem exchange 6 whereat the usual dialling signals set up a connection to the wanted subscriber. Speech signals, after comparison at 30, are modulated at 22 and a pilot signal and fixed frequency telemetry signals applied via hybrids 25 and 23 respectively are also modulated on to the carrier at 22. A second modulation stage may be employed with amplifier 20. The signals are then applied via the usual filter 5, 3 to a power line 1. At the incoming side of a tandem exchange, the pilot signal, which is derived from the feedback path 15, 16, 17 round demodulator 12, adjusts the gain of amplifier 11 in the usual manner. At the outgoing side of the exchange the signals are re-modulated on to the carrier at 22 but in this case relay 26 (operated during the setting up of the connection) prevents a further pilot signal being injected via hybrid 25. At the terminating exchange, where the pilot has no effect on the amplifier 11, the demodulated speech and telemetry signals are routed to their appropriate destinations.