Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

SUBCARRIER IN COMMUNICATIONSAllfilter, with coils having a comparatively low value of Q.The frequencyresponse is given by curve A of Figure 4 and shows discriminationsuch as that used in the radiophoto terminal equipment. The range oflinearity of this filter unit was not as great as desired for anotherapplication so two sections of a resistance-capacitance-type low-passfilter, having the characteristic of curve B, were added. Isolatingvacuum tubes are used for coupling and impedance matching. Curve Cshows the over-all frequency response of the complete unit which hasan exceedingly wide range of linearity.Such a characteristic isnecessary when the ratio of subcarrier tosignal frequency is low, but in some of the applications of subcarrierfrequency modulation, this mode of operation is highly advantageousin the conservation of frequency bandwidth. An actual saving is made2 3 + S 6 7PROPORTIONAL TC FRCQUENCYPig. 4—Frequency-response curves of wide-range frequency discriminator.because if a high value of subcarrier is used in the modulation of ahigher primary carrier then there will be a "waste" space of frequenciesbetween the primary carrier and its nearest sidebands.ConclusionsIn summing up the results and observations with subcarrier frequencymodulation, the outstanding advantage of this system in pointto-pointcommunications is in overcoming the ill effects of unwantedamplitude variations which are always present to some extent in alltransmission circuits. In any system in which the intelligence is conveyedby amplitude variation, any noise wave introduced into the path