Circuitry for a facsimile receiver for regeneration of carrier f

Details Circuitry for a facsimile receiver for regeneration of carrier f Circuitry for a facsimile receiver for regeneration of carrier f

1977-09-12

1978-12-19

Britton, Howard W.

Facsimile and static presentation processing

Facsimile

Recording apparatus

358280, H04N 140

Patent

active

041308395

ABSTRACT:
Circuitry for a facsimile receiver for regenerating a carrier signal from the full-wave rectified signal obtained from a received signal which includes an amplitude modulated suppressed carrier signal and periodic short intervals of unmodulated carrier, each interval being synchronous with a position signal produced at the facsimile receiver each time the phase position of the receiver is reached. The circuitry includes a phase lock loop (PLL) which functions as a sample data PLL. A switching means limits closed loop operation of the circuitry to those times when the short interval unmodulated carrier is received during a time slot provided by the switching means each time the facsimile receiver reaches its phase position. In a preferred embodiment, the loop is also closed (sampled) when other periods of unmodulated carrier is present in the received signal to which the switching means responds. A bandwidth modifying circuit portion connected to the filter for the PLL automatically provides a greater bandwidth for the PLL when the PLL frequency is far from the desired lock frequency. The capture range of the PLL is quite narrow and the filter for the PLL is designed so the filtered error signal responds much slower than the sample rate.

REFERENCES:
patent: 3673322 (1972-06-01), Baxter

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