Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

FREQUENCY MODULATION AND CONTROLBY ELECTRON BEAMS*tByLloyd P. Smith$ and Carl I.ShulmanResearch Department, RCA Laboratories Division,Princeton, N. J.Summary— General formulas for the effect of electron beams on resonantsystems in terms of frequency shift and change in Q are derived from thepoint of view of lumped circuits and from a general electromagnetic fieldstandpoint. A way of introducing the electrons has been found which materiallyenhances their effectiveness in producing a shift of frequency in aresonant system. Measurements of the frequency shift produced by such anelectron beam in a typical geometry were made which check well with valuescalculated from the general theory. Possible amplitude and phase distortionsare calculated when such a beam is used to frequency-modulate a system,and these are found to be negligibly small, even for very high modulatingfrequencies.It is shown that this method of frequency control is ideally suited forfrequency modulation or automatic frequency stabilization of continuouswavemagnetron oscillators using negative-grid-controlled electron beamsfor controlling the frequency of oscillations.MI. Introduction'ANY occasions arise when it is desirable to control the frequencyof a high-frequency oscillating system so rapidlythat only electronic means can be used. The theory of reactiveelectron beams and the computation of the change in frequencyand loading they produce in an oscillating system is presented herefrom two points of view; the first of which is a treatment essentiallybased on lumped-constant concepts, and the second is a general fieldtheoryapproach especially applicable to cavity systems or systems withdistributed constants. The change of frequency and loading can befinally expressed in terms of rather simple formulas.A part of the problem of obtaining the largest frequency shiftpossible for a given number of electrons entering the oscillating electromagneticfield region per second is that of introducing the electronsinto that combination of oscillating electromagnetic field and steadyelectric and magnetic fields for which the largest reactive current isproduced. For many applications it is necessary to obtain this maximumreactive current consistent with the auxiliary condition that* Decimal Classification: R138 X R355.912.1.f Reprinted from Proc. I.R.E., July, 1947.j Now Research Consultant, RCA Laboratories Division.467