Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1979-03-23
1981-02-03
Martin, John C.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
455 92, 455116, 455119, H04N 540, H04B 104
Patent
active
042492149
ABSTRACT:
Television broadcast transmitters are often operated at remote sites and must be remotely controlled. The transmitters often include exciters driving high-power amplifiers. The exciters and high-power amplifiers produce incidental phase modulation of the broadcast signals. An exciter for generating modulated carrier signals at a television video carrier frequency may include compensation for incidental phase modulation in the exciter itself and in the following amplifiers. Such an exciter includes a first modulator for modulating video onto an IF carrier, which is coupled through a power splitter to a second modulator. The second modulator is switched at a frequency equal to the sum of the video and intermediate frequencies to produce the desired modulated carrier. The output of the power divider is coupled to an envelope detector which reconstitutes the video. The reconstituted video is applied to the control input of a phase modulator coupled to the second mixer for producing a phase compensation of the modulated carrier in response to the video amplitude. Remote control of the power output of the exciter is provided by a motorized attenuator. A corresponding adjustment of the incidental phase correction is achieved by connecting the motorized attenuator between the first modulator and the power divider. In order to provide increased phase control range, improved video-frequency rejection and reduced incidental amplitude modulation, the phase modulator is coupled between the carrier-frequency generator and the second modulator. The phase modulator may also be coupled between the power splitter and the second modulator.
REFERENCES:
Irmer et al., "20 KW UHF Television Transmitter With All Solid State Driver For Klystron Amplifiers," Electrical Communication, vol. 48, No. 4, 1973, pp. 436-443.
Martin John C.
Meise William H.
Rasmussen Paul J.
RCA Corporation
Whitacre Eugene M.
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