Rf-modulator

  
Two IC rf modulators convert a suitable baseband video and audio signal up to a low VHF modulated carrier-Channel2 through 6 in the U.S., and 1 through 3 in japan-the LM1889 and the LM2889. Both !Cs are identical regarding the rf modulation function, including pin outs, and can provide either of two rf carriers with de switch selection of the desired carrier frequency. The LM1889 includes a crystal-controlled chroma subcarrier oscillator and balanced modulator for encoding R through Y or U and V color difference signals.
Rf-modulator - schematic

A sound intercarrier frequency lc oscillator is modulated using an external varactor diode. The LM2889 replaces the chroma subcarrier function of the LM1889 with a video de restoration clamp and an internal frequency-modulated sound intercarrier oscillator.




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