Voice guard circuit for a tone receiver

Details Voice guard circuit for a tone receiver Voice guard circuit for a tone receiver

1976-05-17

1977-08-16

Claffy, Kathleen H.

H04M 150

Patent

active

040427900

ABSTRACT:
Analog detection of invalid signal conditions at the input to a Dual Tone Multiple Frequency (DTMF) tone receiver is provided. The average of the voltage peak amplitudes of the signals in the upper and lower bands of the DTMF signal are crossed compared, and if the level in one channel exceeds that in the other channel, or if the level in one channel exceeds that in the other channel by a ratio greater than approximately 3:1, the tone receiver output is inhibited. Also, such an average of the voltage peak amplitudes in the portion of the frequency spectrum above 1700 Hz. of the tone receiver input is compared with the same averages of the high and low bands, respectively. If either of these latter comparisons indicate the ratio of the input component above 1,700 Hz. relative to the respective band signal is greater than approximately 0.25, the tone receiver is inhibited from providing an output.

REFERENCES:
patent: 3780230 (1973-12-01), Bowen
patent: 3795775 (1974-03-01), Coupland
patent: 3851112 (1974-11-01), Kusan
patent: 3875347 (1975-04-01), Alaily

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