Abstract: A demodulator for regenerating and demodulating a carrier signal from a four-phase PSK received signal having a data symbol preamble and a fixed phase (one of four phases) of a particular time width using a synchronous detection type demodulating system (remodulation type demodulating system). The demodulator includes an orthogonal demodulating circuit and a remodulating circuit for regenerating a carrier signal which is the data signal during a preamble transmission period from a received modulated signal. The remodulating circuit includes a demodulator having an AFC circuit for detecting a frequency change using a narrow band filter, means for suppressing frequency changes of the four-phase PSK modulated signal received and means for rendering constant the frequency of the regenerated carrier signal passing through the narrow band filter.

Abstract: In a bandwidth compressed transmission system in which a frequency band of a television signal of 2:1 interlace system is compressed, on an encoder side, by interfield offset subsampling at a first sampling frequency corresponding to a substantially upper limit frequency of the television signal and, after an output signal thus subsampled is applied to a LPF for passing a signal component having an aliased portion resulting from the interfield offset subsampling and having a cut-off frequency substantially equal to one half of the first sampling frequency, by interframe offset subsampling at a second sampling frequency lower than the first sampling frequency and higher than one half of the first sampling, so that a multiplexed subsampled transmission signal which does not include an aliased portion of reverse phase results from the interframe offset subsampling.