| 摘要 |
Synchrodyning apparatus in which a PAM IF signal is mixed with unmodulated carriers nominally at the frequency of the carrier, which unmodulated carriers are in quadrature with respect to each other. E.g., the PAM IF signal may be an intermediate-frequency 8VSB digital television signal. The baseband signals resulting from the mixing procedures are additively combined and differentially combined to generate real and imaginary components of a complex baseband signal. The real component of the complex baseband signal is processed for reproducing the digital signal used to modulate the transmitted RF carrier. An automatic frequency and phase control (AFPC) signal for controlling the oscillator circuitry generating the unmodulated carriers is generated by an AFPC detector responding to the imaginary component of the complex baseband signal or to both components of the complex baseband signal. Various combinations of the synchrodyning apparatus with channel-equalization and echo-suppression filtering are described.
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