Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

416 FREQUENCY MODULATION, Volume IAnother suggested means for overcoming the variation in signallevel in the present telegraph channeling system is the use of automaticvolume control in each channel. However, the use of subcarrier frequencymodulation is preferable because of its inherent nature of conveyingintelligence irrespective of amplitude fluctuations.Still another means of accomplishing the same desired result isuse subcarrier frequency modulation in each of the individual channels.This, in reality, would be a case of frequency-shift keying.Although it provides for satisfactory operation, frequency-shift keyersand limiters and discriminators are needed for each channel.If either amplitude or frequency modulation of a subcarrier is used,the matter of a low ratio of subcarrier frequency to maximum signalfrequency is of importance. If this subcarrier is to modulate a higherfrequencyprimary carrier it is desirable to use as low a value of subcarrieras possible so as to conserve bandwidth or to use a given bandwidthmost efficiently. Results for the subcarrier amplitude-modulationto°"-f—vMJ£/-vw-f-vJ2£g£/r—fB +'Hr-'