4.5 mhz (intercarrier) fm modulator

Abstract From the Canadian patent

Circuitry for producing an extremely linear frequency modulated audio carrier for use in the headend of a video signal distribution system, such as a cable television system. A reference oscillator operating at a relatively high frequency, such as the video carrier frequency generates a, signal which is divided down to a relatively low frequency. A voltage controlled oscillator operating at the relatively low frequency is used to frequency modulate the audio signal. After modulation the audio carrier is upconverted utilizing a signal frequency which is also derived from the original reference frequency, thus providing a stable and linear frequency modulated audio carrier particularly …