Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

COMMON- AND ADJACENT-CHANNEL INTERFERENCE 327a frequency modulation receiver, with perfect limiting and linear phaseshift in the tuned circuits. As x approaches one, the output becomes moreand more like an impulse, until at x = 1, the output has the constant valueone-half except when 2ir\d = x; here the output becomes infinite. The areabetween the line one-half unit above the time axis and the curve for theinstantaneous frequency over one cycle is constant for aH values of x andequals — xfj..This means that as x—>l the output is constant except at2-ir^.t = 7r and at that point is an impulse equal to it(jl times a unit-impulsefunction.When x becomes greater than one, the polarity of the impulse changebut the shape is the same, as shown by Figure 8.2rrpt-Fig. 8—Audio output, x > 1.Average Value of Instantaneous Frequency. If the discriminator is tunedto the frequency w, the average audio output is zero when x < 1. Asshown in Appendix I, the average output is proportional to [a when x >1.The curves of Figure 8 show this shift in average value when e» becomesstronger than d and takes control.Root-Mean-Square Value of Instantaneous Frequency. If the audio outputfrom the discriminator is measured with an root-mean-square meter, thereadings will vary as shown by Figure 9. The output increases uniformlyfrom zero when x = until it rapidly approaches infinity when x = 1.When x > 1 the output decreases uniformly to one as x becomes large.'