(under subclass 295) Systems where any undesired modulation components accompanying a desired modulated carrier wave signal, which components are due to electrical disturbances within the useful frequency band or any undesired carrier wave distortion and which may originate at a source external to the transmitter or which may be generated internally in the transmitter, are reduced, eliminated or compensated for, or where the transmitted signal may, prior to transmission, be distorted in a manner complementary to the distortion introduced in the transmission medium.