Frequency Spectrum of an FM/FM Signal

Abstract

Several authors have attempted to derive a mathematical model that will describe the frequency spectrum of a FM/FM signal. However, to this author's knowledge, none of the mathematical models that have been published is valid when the carrier is modulated by more than one subcarrier. In this paper an expression for a FM/FM signal is derived that is valid when IRIG specifications are applied. Then this expression is manipulated into a form that will yield the frequency spectrum when the carrier is modulated by any number of subcarriers. Then an illustration of a two subcarrier frequency spectrum is presented.