Loudspeaking telephone instrument

Details Loudspeaking telephone instrument Loudspeaking telephone instrument

1987-04-22

1988-05-31

Ng, Jin F.

Telephonic communications

Substation or terminal circuitry

For loudspeaking terminal

379406, H04M 100

Patent

active

047486635

ABSTRACT:
A loudspeaking telephone instrument comprises a transmit path comprising a microphone (1) and comb filter (2); a receive path comprising a comb filter (3), a frequency shifter (4) and a loudspeaker (5); and a hybrid circuit (6). The frequency shifter (4) shifts the frequency of a signal applied to its input by a fixed amount and the comb filters (2,3) are arranged so that the frequency shifted signal falls in their stop bands. This increases the available gain in the loudspeaking telephone instrument before instability occurs. The spacings of the pass and stop bands of the comb filters (2,3) are at a multiple of the frequency by which the frequency shifter shifts that of its input signal.

REFERENCES:
patent: 3022504 (1962-02-01), Stroud et al.
patent: 3567873 (1971-03-01), Peroni
patent: 3585311 (1971-06-01), Berkley et al.
patent: 3622714 (1971-11-01), Berkley et al.
patent: 4456792 (1984-06-01), Courtney-Pratt

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