Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

GENERATION AND DETECTION 163Appendix IIProof that amplitude modulation in a low-deviation phase-modulatedwave can produee frequency-modulation distortion equal approximatelyto the per cent amplitude modulation, if this factor isFirst assume that the phase deviation issmall.sufficiently low to justifythe use of only the first-order sidebands. The signal then has theform of Figure (b).r~ MAX.Fig. (b) = tan -1 sin n = 2ir X modulating frequencyNow let the carrier be amplitude modulated at the same audio frequency,viz:The phase angle is given bye c= E e (X + m sin a t)Letlation.Then2E,E ebe a constant, determined by the amount of phase modu-= tan- 1 Ksin