Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

FREQUENCY MODULATION*!ByS. W. SeeleyRCA License Laboratory, New YorkSummary— This paper, which contains generalized theory of the principalcharacteristics of frequency-modulation systems, is purposely madebroad in its attack in order to achieve simplicity of presentation of fundamentals.Detailed treatment of specific problems associated with this typeof modulation isgiven in the articles listed in the appended bibliography.COMBINATIONphase modulation into one treatment may seem improper, atfirst glance, when the subject to be treated is frequency modulationalone.I. Frequency and Phase Modulationof discussions of frequency modulation andIt has been done in this section of the paper because thetwo are so related that an understanding of both is necessary for atrue picture of either.The simplest conception of a frequency-modulated wave isof onewith unvarying amplitude whose frequency is altered cyclically aboveand below its mean unmodulated value. However, if we consider phasemodulation in its simplest form, it can be seen that frequency modulationalso results therefrom. Consider the case of Figure 1, in which acarrier wave of unvarying amplitude A has its phase advanced andretarded sinusoidally between values of +