Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

:. However,FREQUENCY-MODULATION FIELD TEST 127F-M TheoryThe theory of FM has been presented in the literature 3 4 5- 'since the following pages compare the actual performance in thefield with the theoretical, there is presented for the convenience ofthe reader a very brief review of the reasons why FM is superior,and the nature of the superiority.The advantages of FM over AM in noise suppression are contributedby three factors1. The triangular noise spectrum of FM.2. Large deviation ratios.3. The greater effect of de-emphasis in FM compared to AM.Fig. 14The Triangular Noise SpectrumAn F-M system with a deviation ratio of one has an advantagein signal-to-noise ratio of 1.73 or 4.75 db for tube hiss or other typesof fluctuating noise.Tube hiss consists of a great many closely overlapping impulses.When combined with a steady carrier of fixed frequency, the noise3A Method of Reducing Disturbances in Radio Signaling by a Systemof Frequency Modulation, Edwin H. Armstrong, Proc. I.R.E., pp. 689-740Vol. 24, May, 1936.4Frequency Modulation Characters, Murray G. Crosbv, Proc. I.R Epp. 472-514, Vol. 25, April, 1937.5 The Service Range of Frequency Modulation, Murray G. Crosby, RCAReview, pp. 349-371, January, 1940.