Fundamental and harmonic distortion of waves, frequency-modulated with a single tone

The distortion of single-tone frequency modulation by passive networks whose amplitude and phase characteristics are non-linear with frequency is considered in some detail. A new approximate formula has been developed by extension of earlier methods, and its use, supplemented by the quasi-stationary approximation and by direct Fourier analysis, permits evaluation of distortion levels over ranges of parameters previously excluded. A number of examples are given, comparison being made where possible with results obtained by other methods. Particular attention is given to distortion of the amplitude and phase of the fundamental, this being of importance in connection with television baseband requirements. An attempt is made to clarify certain theoretical aspects, such as the validity of the `quasi-stationary¿ solution, which have been the subject of controversy.