Compatible four channel fm system

Claim 2

A compatible four channel audio system for use in conjunction with an F. M. radio transmitter having a composite signal modulated on the carrier thereof consisting of a main channel, a 19 kHz synchronizing pilot signal, a first sub-channel which is the second harmonic of said pilot signal and a second sub-channel which is the fourth harmonic of said pilot signal, wherein said composite signal is generated by providing first, second, third and fourth audio signals, providing a 76 kHz sub-carrier frequency and utilizing said 76 kHz frequency to switch a first audio gate between the first and second audio signals and a second audio gate to switch between said third and fourth audio signals, providing a 38 kHz sub-carrier frequency and utilizing said 38 kHz frequency to switch a third audio gate between the outputs of the said first two audio gates, providing a pilot signal of 19 kHz and combining said pilot signal with the output of said third audio gate and utilizing this composite signal to modulate an F.M. transmitter.

Claim 3

A decoder for demodulating the four channel composite signal as generated by the system of claim 1, comprising in combination: a. means for extracting the 19 kHz pilot signal, b. means for providing a first switching frequency at twice said 19 kHz frequency, c. first audio gate means for switching said composite signal at said first switching frequency into two signals, d. means for providing a second switching frequency at twice said first switching frequency, and c. second audio gate means for switching each of said two signals generated by said first audio gate means at said second switching frequency to provide four audio output signals.

Claim 4

A four channel audio system for use in conjunction with an F. M. radio transmitter for transmitting a composite signal which composite signal includes a main channel with first, plus second, plus third and plus fourth audio signals combined thereon, a pilot signal removed from said main channel, a first suppressed sub-channel which is the second harmonic of said pilot signal, said first sub-channel having first, plus second, minus third, minus fourth audio signals and in quadrature therewith first, minus second, minus third and plus fourth audio signals modulated thereon and a second suppressed sub-channel centered on a frequency twice that of said first sub-channel having first, minus second, plus third, minus fourth audio signals thereon, means for doubling said pilot signal and means for utilizing said doubled pilot signal to switch between first plus second and third plus fourth audio signals to obtain two signals, quadrupling said pilot signal and utilizing said quadrupled pilot signal to switch between the first and second audio signals and between the third and fourth audio signals to obtain four audio signals.

Claim 5

A four channel audio system for use in conjunction with an F. M. radio transmitter for transmitting a composite signal which composite signal includes a main channel with first, plus second, plus third and plus fourth audio signals combined thereon, a pilot signal removed from said main channel, a first suppressed sub-channel which is the second harmonic of said pilot signal, said first sub-channel having first, plus second, minus third, minus fourth audio signals and in quadrature therewith first, minus second, minus third and plus fourth audio signals modulated thereon and a second suppressed sub-channel centered on a frequency twice that of said first sub-channel having first, minus second, plus third, minus fourth audio signals thereon, means for doubling said pilot signal and means for utilizing said doubled pilot signal to switch between first plus second and third plus fourth audio signals to obtain two signals, quadrupling said pilot signal and utilizing said quadrupled pilot signal to switch between the first and second audio signals and between the third and fourth audio signals to obtain four audio signals.

Claim 6

The four channel audio system of claim 3 wherein the F.M. signal contains the following components: a. a main channel extending up to 15 kHz having first, plus second, plus third, plus fourth audio signals, b. a 19 kHz pilot signal, c. a 38 kHz suppressed sub-channel having first, plus second, minus third, minus fourth audio signals and in quadrature therewith first, minus second, minus third, and plus fourth audio signals modulated thereon, d. a 76 kHz suppressed sub-channel having first, minus second, plus third, minus fourth audio signals thereon, e. means to provide a 38 kHz signal and to utilize said signal to switch between said first plus second and third plus fourth audio signals, and f. means to provide a 76 kHz signal and to utilize said signal to switch between said first and second audio signals and between said third and fourth audio signals.

Claim 7

A four channel F.M. system which is fully compatible with existing mono and stereo standards wherein there is employed a composite signal having a main channel extending to 15 kHz from the carrier frequency of an F.M. transmitter with plus first, plus second, plus third and plus fourth audio signals combined thereon, a 19 kHz pilot signal removed from said carrier frequency, a first sub-channel which is the second harmonic of said pilot signal, said first sub-channel containing two sub-carriers, the first modulated with the audio signal: plus first, plus second minus third minus fourth audio signals and in quadrature therewith the second subcarrier modulated with the audio signal: plus first, minus second, minus third and plus fourth audio signals and a second sub-channel centered on the fourth harmonic of said pilot signal containing a sub-carrier modulated with the audio signal: plus first, minus second, plus third and minus fourth audio signals.

Claim 8

A four channel F.M. system which is fully compatible with existing mono and stereo standards wherein there is employed a composite signal having a main channel extending to 15 kHz from the carrier frequency of an F.M. transmitter with plus first, plus second, plus third and plus fourth audio signals combined thereon, a 19 kHz pilot signal removed from said carrier frequency, a first sub-channel which is the second harmonic of said pilot signal, said first sub-channel containing two sub-carriers, the first modulated with the audio signal: plus first, plus second minus third minus fourth audio signals and in quadrature therewith the second subcarrier modulated with the audio signal: plus first, minus second, minus third and plus fourth audio signals and a second sub-channel centered on the fourth harmonic of said pilot signal containing a sub-carrier modulated with the audio signal: plus first, minus second, plus third and minus fourth audio signals.