Method of subcarrier multiplication which preserves AM Information in FM systems

Claim 2

A circuit for processing a signal including a carrier which has been amplitude and frequency modulated to alter carrier frequency and frequency deviation of the signal by a selected factor while preserving the amplitude modulation of the signal, said circuit comprising: means for removing the amplitude modulation from the signal to generate a second signal which includes the carrier frequency and the frequency modulation; means for mixing the signal with said second signal to generate at an output of said mixing means a plurality of mixing products which include at least sum and difference products of the signal and said second signal; and means for filtering said output of said mixing means to select the mixing product which includes the carrier frequency and frequency deviation altered by the selected factor along with the amplitude modulation.

Claim 3

The circuit according to claim 1 wherein said carrier is an audio subcarrier for use in a FM television system.

Claim 4

The circuit according to claim 2 wherein said FM television system is a supertrunk system.

Claim 5

The circuit according to claim 2 wherein said amplitude modulation on said audio subcarrier is television descrambling information.

Claim 6

The circuit according to claim 1 wherein the selected factor is equal to the ratio N/M, where N and M are integers, said circuit further comprising dividing means coupled between said removing means and said mixing means, for dividing the carrier frequency and the frequency deviation of said second signal by said integer M, and the integer N is chosen by selecting the appropriate mixing product.

Claim 7

The circuit according to claim 5 wherein said selected factor N/M is greater than 1 and said circuit comprises a portion of an FM transmitter.

Claim 8

The circuit according to claim 5 wherein said selected factor N/M is less than 1 and said circuit comprises a portion of an FM television receiver.

Claim 9

The circuit according to claim 5 wherein said signal comprises an audio subcarrier at a frequency of 5.75 megahertz.

Claim 12

The method according to claim 9 and comprising the step of dividing the carrier frequency and frequency deviation of said second signal by the integer M prior to said step of mixing.

Claim 13

The method according to claim 9 wherein the selected factor (N/M) is a greater than 1.

Claim 14

The method according to claim 9 wherein the selected factor (N/M) is less than 1.

Claim 15

The method of claim 9 wherein said amplitude modulation on said signal is television descrambling information.

Claim 16

Circuitry for processing a first signal including a carrier which has been amplitude and frequency modulated to alter carrier frequency and frequency deviation of the first signal at a transmitter side and at a receiver side of an FM television system to prevent spectral overlap of signals, while preserving the amplitude modulation of the first signal, said circuitry comprising: a) a first circuit, comprising a portion of an FM television transmitter, for increasing the frequency and frequency deviation of the first signal by a first selected factor (N/M), where N and M are integers, while preserving the amplitude modulation, said first circuit comprising: i) first removing means for removing the amplitude modulation from the first signal to generate a second signal which includes the carrier frequency and the frequency modulation of the first signal; ii) first mixing means for mixing the first signal with said second signal to generate at an output of said first mixing means a plurality of mixing products which include at least sum and difference products of the first and the second signals; and iii) first filtering means for filtering said output of said first mixing means to select the mixing product as a third signal which includes a carrier frequency and a frequency deviation altered by the first selected factor (N/M) along with the amplitude modulation; and b) a second circuit, comprising a portion of a FM television receiver, for decreasing the frequency and frequency deviation of the third signal by a second selected factor (M/N), where the second selected factor (M/N) is a reciprocal of the first selected factor (N/M), while preserving the amplitude modulation, said second circuit comprising: i) second means for removing the amplitude modulation from said third signal to generate a fourth signal which includes the carrier frequency and the frequency deviation of said third signal. ii) second means for mixing the third signal with the fourth signal to generate at an output of said second mixing means a plurality of mixing products which include at least the sum and difference products of the third and the fourth signals; and iii) second means for filtering said output of said second mixing means to select the mixing product as a fifth signal which includes a carrier frequency and a frequency deviation altered by said second selected factor (M/N) and containing the amplitude modulation, wherein the carrier frequency, frequency deviation, frequency and amplitude modulation of the fifth signal are equal to the carrier frequency, frequency deviation, frequency and amplitude modulation, respectively, of the first signal.

Claim 17

Circuitry for processing a first signal including a carrier which has been amplitude and frequency modulated to alter carrier frequency and frequency deviation of the first signal at a transmitter side and at a receiver side of an FM television system to prevent spectral overlap of signals, while preserving the amplitude modulation of the first signal, said circuitry comprising: a) a first circuit, comprising a portion of an FM television transmitter, for increasing the frequency and frequency deviation of the first signal by a first selected factor (N/M), where N and M are integers, while preserving the amplitude modulation, said first circuit comprising: i) first removing means for removing the amplitude modulation from the first signal to generate a second signal which includes the carrier frequency and the frequency modulation of the first signal; ii) first mixing means for mixing the first signal with said second signal to generate at an output of said first mixing means a plurality of mixing products which include at least sum and difference products of the first and the second signals; and iii) first filtering means for filtering said output of said first mixing means to select the mixing product as a third signal which includes a carrier frequency and a frequency deviation altered by the first selected factor (N/M) along with the amplitude modulation; and b) a second circuit, comprising a portion of a FM television receiver, for decreasing the frequency and frequency deviation of the third signal by a second selected factor (M/N), where the second selected factor (M/N) is a reciprocal of the first selected factor (N/M), while preserving the amplitude modulation, said second circuit comprising: i) second means for removing the amplitude modulation from said third signal to generate a fourth signal which includes the carrier frequency and the frequency deviation of said third signal. ii) second means for mixing the third signal with the fourth signal to generate at an output of said second mixing means a plurality of mixing products which include at least the sum and difference products of the third and the fourth signals; and iii) second means for filtering said output of said second mixing means to select the mixing product as a fifth signal which includes a carrier frequency and a frequency deviation altered by said second selected factor (M/N) and containing the amplitude modulation, wherein the carrier frequency, frequency deviation, frequency and amplitude modulation of the fifth signal are equal to the carrier frequency, frequency deviation, frequency and amplitude modulation, respectively, of the first signal.

Claim 18

The circuit according to claim 14 wherein said first circuit further comprises dividing means, coupled between said first removing means and said first mixing means for dividing the carrier frequency and frequency deviation of said second signal by said integer M.

Claim 19

The circuit according to claim 14 wherein said second circuit further comprises dividing means, coupled between said second removing means and said second mixing means, for dividing the carrier frequency and frequency deviation of said fourth signal by said integer N.

Claim 20

A circuit for processing an input signal including a carrier which has been amplitude and frequency modulated to alter carrier frequency and frequency deviation of the input signal by a selected factor (N/M), where N and M are integers, while preserving the amplitude modulation of the input signal, said circuit comprising: removing means for removing the amplitude modulation from the input signal to generate a second signal which includes the carrier frequency and the frequency modulation; dividing means coupled to said removing means for dividing the carrier frequency and frequency deviation of the second signal by the integer M; mixing means for mixing the input signal with an output of said dividing means to generate a plurality of mixing products which include at least sum and difference products of the input signal and the output of the dividing means; and selecting means coupled to said mixing means for selecting a mixing product which includes the carrier frequency and frequency deviation altered by the selected factor (N/M) along with the amplitude modulation, where the integer N of the selected factor (N/M) is chosen by selecting the appropriate mixing product.

Claim 21

A circuit for processing an input signal including a carrier which has been amplitude and frequency modulated to alter carrier frequency and frequency deviation of the input signal by a selected factor (N/M), where N and M are integers, while preserving the amplitude modulation of the input signal, said circuit comprising: removing means for removing the amplitude modulation from the input signal to generate a second signal which includes the carrier frequency and the frequency modulation; dividing means coupled to said removing means for dividing the carrier frequency and frequency deviation of the second signal by the integer M; mixing means for mixing the input signal with an output of said dividing means to generate a plurality of mixing products which include at least sum and difference products of the input signal and the output of the dividing means; and selecting means coupled to said mixing means for selecting a mixing product which includes the carrier frequency and frequency deviation altered by the selected factor (N/M) along with the amplitude modulation, where the integer N of the selected factor (N/M) is chosen by selecting the appropriate mixing product.

Claim 22

The circuit according to claim 17, wherein said selecting means comprises a filter.