CATV converter having phase locked loop for sound carrier wave frequency control

Claim 1

A CATV converter comprising: a tuner receiving an input CATV signal for a signal of a selected channel; first branching means for bifurcating the selected signal from the tuner into a video carrier and a sound carrier; an audio demodulator receiving the sound carrier for demodulating the sound carrier into an audio signal and providing the audio signal to an audio modulator; second branching means for bifurcating the video carrier from the first branching means into two parts; a mixer receiving a first part of said branched video carrier and a sound carrier output from said audio modulator for providing an output TV signal; a phase locked loop circuit receiving as inputs a second part of said branched video carrier and a part of the sound carrier output of said audio modulator for providing an output control signal to said audio modulator representing a selected frequency difference to be maintained between a frequency of the video carrier and a frequency of the sound carrier output provided to said mixer; and said audio modulator receiving as inputs the audio signal from said audio demodulator and the output control signal of said PLL circuit for providing the sound carrier output having a said sound carrier output frequency which is variably modulated in accordance with the output control signal of said PLL circuit in order to maintain said frequency difference from the video carrier frequency.