Abstract: The useful bandwidth of a bandwidth-limited input signal (s(t)) is reduced, to obtain a coded signal (q(t)) by forming a combined input and feedback signal, low-pass filtering the combined signal, and passing the low-pass filtered signal through a feedback loop which includes symmetrical frequency-voltage (f/V) conversion, substantial amplification, and voltage-frequency (V/f) reconversion, the reconverted signal being combined with the input signal in a multiplier, the coded output signal being derived from the output of the low-pass filter. Amplification of the amplifier is so high that the bandwidth of the resulting frequency-modulated feedback signal is greater than the bandwidth of the original input signal. The resulting coded signal can be decoded by derived scanning signals which are combined with bandwidth-enhanced coded signals and processed in an inversion matrix for subsequent reconstitution of the original signal.