Method for transmitting-end bandwidth compression of an analog signal and for receiving-end expansion of the transmitted signal and a device to carry out the method

摘要

A method is devised in which an analog signal whose speech-band-limited bandwidth is compressed at the transmitting end to part of its bandwidth, preferably to half of its bandwidth, and the signal transmitted in compressed form is expanded at the receiving end to the limited full bandwidth. For transmitting-end compression, the bandwidth-limited analog input signal undergoes full-wave rectification, in parallel with which it is converted at each of its zero passages into square-wave pulses and simultaneously phase-shifted through 90@. The full-wave-rectified signal in unmodified form and in inverted form, half-frequency square-wave pulses and both the positive and negative components of the phase-rotated and subsequently rectified signal are then fed to a selection switching arrangement with a built-in approximation function; the amplitude of the output signal of the selection switching arrangement is dimensioned in such a way that, following low-pass filtering of the applied frequencies at half the bandwidth, its envelope has a sinusoidal shape at half the frequency. For receiving-end expansion, the signal transmitted in compressed form undergoes full-wave rectification, is then differentiated and a first low-pass filtering is carried out to correct its amplitude, followed by a further low-pass filtering to limit the frequencies to the specified bandwidth.