Noise Loading of FM Systems the Noise-Power-Ratio (NPR) and Customer Requirements

Amplitude and phase non-linearities in multichannel FM transmission systems must be closely controlled to avoid excessive intermodulation noise in the derived message channels. Though parameters may be measured individually, their combined effect on distortion performances most directly measured by applying a standard test signal to the FM system which closely simulates the working multi-channel baseband signal. For high capacity systems, this baseband signal is closely approximated by a band of Gaussian (white) noise, band-limited at the same frequencies as the working baseband.