Method and apparatus for low cost audio scrambling and descrambling

A method of descrambling scrambled non-inverted frequency spectrum translated single sideband audio information signals capable of reproducing an original audio signal having a frequency of about 50 Hz to about 15 Khz said method comprising the steps of:

• inputting a scrambled frequency single sideband audio input signal;
• generating a first modulation carrier signal having a frequency greater than the highest frequency in the audio input signal;
• double sideband modulating said scrambled audio signal into said first modulation frequency, a first upper sideband signal and a first lower sideband signal;
• filtering out said first modulation fundamental frequency, harmonics, said upper sideband signal, harmonics from said double sideband signal produced by said harmonics of said first modulation fundamental frequency and all the harmonics of said lower sideband signal from said double sideband signal and passing said lower sideband signal;
• generating a second modulation carrier frequency having a frequency less than said first modulation frequency;
• double sideband modulating said first lower sideband signal with said second modulation carrier frequency to produce a second modulating frequency, a second upper sideband signal and a second lower sideband signal;
• filtering out said second modulating frequency, a second upper sideband signal to pass said second lower sideband signal to produce a descrambled audio signal:
• whereby using and selecting said first and second modulation carrier signals, said first and second modulation means and said first and second filter means produces said descrambled audio signal containing substantially no audible whistle component.

A system of scrambling of original audio signal having a frequency range 50 Hz to about 15 Khz produce a non-inverted frequency translated signal comprising:

• an audio input signal with a frequency range of 50 Hz. to 15 KHz.;
• means for generating a first modulation carrier signal having a frequency greater than the highest frequency in the original audio signal;
• first modulating means for quadrature sideband modulating said original audio signal into a first lower sideband signal;
• first filtering means for filtering out said first modulation fundamental frequency and at least a majority of harmonic frequencies of said first modulation fundamental frequency, said upper sideband signal and harmonic signals produced by said quadrature signal and passing said first lower sideband signal;
• means for generating a second modulation carrier frequency having a frequency higher than said first modulation frequency;
• second modulating means for double sideband modulating said first lower sideband signal with said second modulation carrier frequency to produce a second modulating frequency, a second upper sideband signal and a second lower sideband signal;
• means for filtering to pass said second lower sideband signal to produce a scrambled audio signal;
• whereby use and selection of said first and second modulation carrier signals, said first and second modulation means and said first and second filter means is to produce a scrambled audio signal at a low cost.

A method of scrambling of an original audio signal producing a non-inverted frequency translated signal said method comprising the steps of:

• inputting an audio signal with a frequency range of 50 Hz. to 15 KHz.;
• generating a first modulation carrier signal having a frequency greater than the highest frequency in the original audio signal;
• quadrature modulating said original audio signal into a first lower sideband signal;
• filtering out said first modulation fundamental frequency and harmonics of said first modulation frequency, said upper sideband signal, harmonics from said modulated signal produced by said harmonics of said first modulation fundamental frequency and passing said first lower sideband signal;
• generating a second modulation carrier frequency having a frequency higher than said first modulation frequency;
• double sideband modulating said first lower sideband signal with said second modulation carrier frequency to produce a second modulating frequency, a second upper sideband signal and a second lower sideband signal;
• filtering second modulating frequency, said second upper sideband signal and said second lower sideband signal to pass said second lower sideband signal to produce a scrambled audio signal;
• whereby use and selection of said first and second modulation carrier signals, said first and second modulation means and said first and second filter means is to produce a descrambled audio signal at a low cost.