Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

88 FREQUENCY MODULATION, Volume Icoupling between L\ and L 2 ,a linear frequency modulation may beobtained.During the frequency modulation transmission the transmitteramplifiers and frequency doublers were operated class C throughoutso as to limit off any amplitude modulation introduced in the modulatoror otherwise.Fig. 2— Circuit diagram of frequency modulation receiver showing the conversionfilters and detectors.An amplitude modulating stage was included inthe transmitterso that the transmitter could be adjusted for amplitude modulationand direct comparison could be made between frequency modulationand amplitude modulation.The ReceiverA schematic diagram of the frequency modulation receiver is shownin Fig. 2. Energy at the superheterodyne intermediate frequency is fedto the two coupling tubes, A and B, having the conversion filters forconverting the frequency modulation into amplitude modulation inFREOUENCY-Fig. 3— Characteristics of the conversion filters used to convert frequencymodulation into amplitude modulation for detection.their plate circuits. The characteristics of these two filters are given bythe curves A and B in Fig. 3. The carrier frequency F c ,is tuned to themiddle of the linear portion of the sloping characteristic formed by thetwo tuned circuits connected as shown. By adjusting the tuned circuitsso that the points of maximum and minimum output fall outside of theintermediate-frequency channel, only the linear portion of the characteristicsare utilized. The outputs of these filters are fed to the detectors