Apparatus for method for selectively demodulating and remodulating alternate channels of a television broadcast

A method of selecting, demodulating and remodulating a signal from within a broadcast containing a video signal and two or more accompanying signals, said method comprising the steps of:

• selecting one of said two or more accompanying signals to produce a selected signal;
• demodulating said selected signal;
• frequency modulating said selected signal to produce a remodulated signal in frequency spectrum of said broadcast;
• and
• combining said remodulated signal with said video signal and at least one other of said two or more accompanying signals which was not demodulated.

Apparatus for selecting, demodulating and remodulating a signal from within a broadcast containing a video signal and two or more accompanying signals, said apparatus comprising:

• means for selecting one of said two or more accompanying signals to produce a selected signal;
• means for demodulating said selected signal;
• means for frequency modulating said demodulated signal to produce a remodulated signal in the frequency spectrum of said broadcast;
• and
• means for combining said remodulated signal with said video signal and at least one other of said two or more accompanying signals which was not demodulated.

A circuit for selectively demodulating a television signal comprising a video signal and first and second sound signals, said circuit comprising:

• a tuner for tuning to said television signal;
• an intercarrier demodulator, coupled to said tuner, for demodulating said tuned television signal to provide an intercarrier sound signal including said first and second sound signals;
• a first bandpass filter, coupled to said intercarrier demodulator and tuned to a first passband including said first sound signal, for filtering said intercarrier sound signal and outputting a first filtered sound signal through a first bandpass filter output;
• a second bandpass filter, coupled to said intercarrier demodulator and tuned to a second passband including said second sound signal, for filtering said intercarrier sound signal and outputting a second filtered sound signal through a second bandpass filter output;
• an FM demodulator for demodulating one of said first and second filtered sound signals to provide a demodulated sound signal;
• a switch, coupled between said outputs of said first and second bandpass filters and said FM demodulator, for selecting one of said first and second filtered sound signals and providing said selected one to said FM demodulator;
• means for tuning said FM demodulator in accordance with said selected signal to thereby selectively tune said FM demodulator to said first or second filtered sound signal;
• a modulator, coupled to said FM demodulator, for remodulating said demodulated sound signal to produce a remodulated sound signal;
• and
• means for mixing said remodulated sound signal with said second filtered sound signal and said video signal.

A circuit for frequency demodulating a frequency modulated signal, comprising:

• a frequency modulation demodulator having an input for accepting the frequency modulated signal, an output for providing a demodulated signal, and means for controlling said demodulator to change a tuned frequency of said demodulator by applying one of two predetermined fixed phase shifts to said frequency modulated signal, each of said predetermined fixed phase shifts corresponding to a different FM carrier frequency, wherein said applied one predetermined fixed phase shift determines which FM carrier frequency is demodulated;
• a tank circuit, coupled to said means for controlling said demodulator, comprising an inductor and a capacitor, said tank circuit establishing said tuned frequency;
• and
• a varactor diode, coupled to said tank circuit and responsive to a selectable control voltage having one of a plurality of fixed voltage levels, for changing said tuned frequency in accordance with said selectable control voltage.