Posted on Dec 1, 2012

This high-performance video-camera link transmits signals from your video camera to your VCR, or from your VCR to TVs throughout your home. The first stage of the rf chain is a crystal-controlled oscillator, Q1, with a frequency of 60 to 65 MHz, which is one-eighth of the final output frequency. The oscillator produces a signal of about +6 dBm (4 mW) that drives three stages of frequency doublers. The combined action of those doublers multiplies the input frequency by eight for a final output frequency of (nominally) 500 MHz.

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Double-tuned circuits are used between each stage to help reduce spurious outputs that might cause unwanted interference. The video input signal from your VCR, video camera, etc. drives a video modulator, Q6 and Q7, that adds the video signal to the +12 V fine supplying power to the final doubler, Q4, and the output amplifier, Q5. That method of modulation is similar to the way a conventional AM-radio transmitter is modulated. The video modulator has a nominal bandwidth of five MHz. The audio input is applied to QS, which operates as a VCO running at a nominal frequency of 4;5 MHz to produce the modulated sound carrier. For simplicity, QS is a free-rurming oscillator, since the ±25 kHz frequency deviation that is required would be very difficult to produce at that frequency with a crystal-controlled oscillator. Besides, most TV sound systems will accept a ±10 kHz error in the sound-carrier frequency without producing undue distortion, and that greatly simplifies the circuitry required. The kit is available from North Country Radio, P.O. Box 53, Wykagyl Station, NY 10804.

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