System for transmitting low frequency tones through a digital lo

Details System for transmitting low frequency tones through a digital lo System for transmitting low frequency tones through a digital lo

1988-11-01

1990-02-20

Ng, Jin F.

Telephonic communications

Telephone line or system combined with diverse electrical...

Having transmission of a digital message signal over a...

379 50, 379 64, 370 76, 3701102, 370 8515, H04M 1106

Patent

active

049032925

ABSTRACT:
A system for use in a digital loop carrier (DLC) which allows low frequency (sub-audible) tones such as those used with alarm systems to be transmitted from one end of the DLC to the other end even though the DLC has been designed to reject signasl below 200 Hz. The system may be added to an already installed DLC or included with the DLC prior to installation. At the end of the DLC from which the low tone is to be transmitted, the system controls the amplitude of the tone so that it can be encoded for transmission within a predetermined window. The DLC allows such low frequencies to be transmitted through the window while still rejecting 60 Hz signals (and its lower order harmonics). The controlled low tone and the voice signals are combined for transmission to the other end. At the other end, the decoded low tone is amplified by the system and then recombined with the decoded voice signals for use therein.

REFERENCES:
patent: 4262283 (1981-04-01), Chamberlain et al.
patent: 4442320 (1984-04-01), James et al.
patent: 4521643 (1985-06-01), Dupuis et al.
National Semiconductor Corporation catalog entitled, "Telecommunications Data Book", 1987 edition, pp. 1-119 and 1-125 entitled TP3040/TP3040-1/TP3040A/TP3040A-1 PCM Monolithic Filter.

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