On the Performance of FM Communications in the Presence of RF Noise

A critical view is taken of some common notions of input signal-to-noise ratio ``thresholds´´ below which frequency modulation radio links become inoperative but above which highly satisfactory communications result. Experimentally derived curves are shown giving output vs input S/N´s for three FM receiver bandwidths and a signal employing sine-wave modulation. When the experimental FM curves are compared with theoretical curves for AM, DSB, and SSB, it becomes clear that the ``threshold´´ concept is extremely misleading. FM systems can enjoy a competitive output S/N for low input S/N against uniform RF noise, while against narrow-band RF noise, wide-band FM is superior to the other systems for practical output S/N.