Loudspeaking telephone with a frequency shifting circuit

Details Loudspeaking telephone with a frequency shifting circuit Loudspeaking telephone with a frequency shifting circuit

1988-03-08

1990-09-04

Ng, Jin F.

Telephonic communications

Substation or terminal circuitry

For loudspeaking terminal

379388, 381 94, H04M 908

Patent

active

049550551

ABSTRACT:
A loud speaking telephone has separate volume level control circuits positioned in the transmit and receive paths, respectively. The frequency is shifted in at least one of the paths to provide a signal which is less likely to produce echos or singing. A comparator compares the levels in the send and receive paths to produce a control signal. The control signal adjusts the volume level controls to prevent singing.

REFERENCES:
patent: 3257510 (1966-06-01), Burkhard
patent: 3894187 (1975-07-01), Shibata et al.
patent: 3952166 (1976-04-01), Kato et al.
patent: 4641339 (1987-02-01), Stottlemyer
patent: 4689818 (1987-08-01), Ammitzboll
patent: 4748663 (1988-05-01), Phillips et al.
patent: 4819263 (1989-04-01), Franklin
The 4A Speakerphone-Hands-Down Winner, Bell Laboratories Record, pp. 233-237, Sep. 1973.
Functional Design of a Voice-Switched Speakerphone, The Bell System Technical Journal, pp. 649-668, May 1961.
Fundamental Considerations in the Design of a Voice-Switched Speakerphone, The Bell System Technical Journal, pp. 265-293, Mar. 1960.
Loudspeaking Telephone Circuit, U.S. Pat. No. 3,952,166.
T. Brook; "A Frequency Shifter for Public Address Systems"; Electronics Australia; vol. 37, No. 5; Aug. 1975; pp. 54, 55, 57, 59.

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