Abstract: A differential signal circuit employing a local decoder and comparator to forecast a reference amplitude to be coded by a non-linear coding system. A non-linear coding means connected to an controlled by the output of the forecast means adaptively varies a non-linear component of such reference amplitude. The reference amplitude to be coded is supplied to the coding means and the reference amplitude preceding the reference amplitude to be coded is supplied to the forecast means.

Abstract: A pilot signal transmission system is disclosed for the transmission of a digital signal in the form of a multilevel amplitude signal. A synchronizing pilot signal, whose frequency is an integral fraction of the Nyquist frequency of a base band signal or equal to the carrier frequency of an amplitude modulated signal, is transmitted while being coupled in in-phase relation with composite vectors of those components of the digital signal lying in the neighborhood of the frequency of the pilot signal. The transmitted signal is applied to a receiver, wherein the components neighboring the pilot signal frequency are extracted substantially symmetrically with respect to the pilot signal frequency to reproduce the pilot signal and the level of the pilot signal at the time of multilevel decoding is cancelled by a signal of a waveform having a constant amplitude for a certain period of time such as a rectangular, trapezoidal or like wave of a period corresponding to that of the pilot signal.