Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

92 FREQUENCY MODULATION, Volume Iaural observations indicated that the carrier and not the side bandshad faded. The presence of second harmonic is very evident. It hasbeen conjectured that frequency modulation might be less susceptibleto the effects of carrier fading because of the fact that the modulatedenergy is distributed among the side bands to a greater extent; consequently,the detected output is not as dependent for its value upona single frequency in the transmission medium as is amplitude modulation.The observations did indicate that with frequency modulation,frWmiFig.6— Frequency and amplitude modulation wave form oscillograms showingthe distortion due to fading.A, B, and C. Amplitude modulation, 300 cycles.D, E, F, G, and H. Frequency modulation, 300 cycles.I, J, and K. Amplitude modulation, 1000 cycles.L, M, N, O, and P. Frequency modulation, 1000 cycles.the output was more constant; the quality of this output, however,prevented itsconstancy from being of any value for the purpose forwhich it was intended. This observation tends to indicate the advantageof systems wherein telegraph transmitters are frequency modulatedto effect a frequency diversity to reduce fading.Diversity DataIn general the diversity experiments indicated that on both frequencyand amplitude modulation the lower modulation frequenciesproduced outputs from the two receivers which remained in phase. Asthe modulation frequency was increased, the tendency toward phase