Transmission circuit for modems employing frequency shift keying

Details Transmission circuit for modems employing frequency shift keying Transmission circuit for modems employing frequency shift keying

1983-06-24

1986-02-25

Safourek, Benedict V.

Pulse or digital communications

Repeaters

Testing

375 65, 331179, 332 9R, 332 16R, H03C 302, H03K 706

Patent

active

045731659

ABSTRACT:
An FSK modem transmission circuit which includes a modulator adapted to sctably produce pairs of low and high frequency carrier waves in any combination of up to five frequencies specified in international and U.S. standards. The modulator circuit includes a regenerative feedback loop which generates a triangular carrier wave at a frequency determined by the resistance of a resistor network having five different settings selected by switches therein controlled by the data signal and by logic control signals. The transmission circuit also includes a filter which modifies the waveform of the transmitted carrier wave to suppress odd harmonics thereof, thereby isolating the carrier wave from the modem receiver circuit which is coupled to the transmission circuit by a hybrid coupler.

REFERENCES:
patent: 3659031 (1972-04-01), Adachi
patent: 3659048 (1972-04-01), Zuerblis et al.
patent: 3878484 (1975-04-01), Hekimian
patent: 4232862 (1982-04-01), Boudault et al.
patent: 4320521 (1982-03-01), Balakrishnan et al.

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