Distortion in Frequency-Modulation Systems Due to Small Sinusoidal Variations of Transmission Characteristics

It is shown that the distortion generated in fm systems by small sinusoidal ripples on either group delay or amplitude characteristics can be evaluated in terms of the distortion due to a single echo. Using results already established for echo distortion, curves are plotted relating intermodulation distortion of a frequency-division-multiplex signal to the amplitude, periodicity, and location of the small sinusoidal ripple for a 600 channel system. These curves are of value in estimating permissible limits of variation of transmission characteristics over the significant rf band.