| 摘要 |
A privacy code-type signal transmission system includes a transmitter having a signal sampler for producing analog samples of an analog audio signal, an analog to digital converter, a scrambler, a multi-level analog former and modulator means. The analog to digital converter converts each analog sample into a parallel n bit digital signal. The parallel n bit digital signal is scrambled by a digital scrambler to produce a second parallel n bit digital signal. The second n bit digital signal is input to a multi-level former having 2n different levels, the output of which is a 2n level analog signal which is suitably modulated for transmission to a receiver. The receiver demodulates the 2n level analog signal and with a level discriminator converts the demodulated signal to a scrambled digital signal corresponding to the scrambled digital signal produced at the transmitter. The original analog audio signal is then recovered by descrambling the digital signal and applying the descrambled digital signal to a digital to analog converter. This system eliminates any need for parallel-serial and serial-parallel converters, as well as frame sync insertion and extraction circuits necessary in conventional privacy code-type transmission systems.
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