H - Electricity – 04 – M
Patent
H - Electricity
04
M
379/11, 379/36
H04M 17/02 (2006.01) H04M 3/00 (2006.01)
Patent
CA 1080865
ABSTRACT OF THE DISCLOSURE An out-of-band signaling method and apparatus are pro- vided to facilitate the adaptation of payphones to telephone systems, as for example subscriber carrier systems. Part of the speech band is made unavailable to the subscribers and is employed for signaling DC line conditions from one end of the telephone system to the other. The apparatus includes at each end of the telephone system a first hybrid transformer connecti- ble with a paystation or central office respectively and a second hybrid transformer connectible with the telephone system. A voice frequency transmit branch is connected be- tween coils of the transformer and includes a low pass filter to limit transmitted voice frequencies to a selected band with an upper cut-off frequency. A voice frequency receive branch is connected between other coils of the transformers and in- cludes a second low pass filter. Signaling circuitry con- nected with the voice frequency branches between the trans- formers transmits and detects signalling tones above the upper cut-off frequency.
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