Zero-Crossing Properties of Angle-Modulated Signals

Most engineers accept that an angle-modulated signal can be demodulated given only its zero crossings. Unfortunately, proofs of this fact tend to be either quite complicated and devoid of physical insight or to incorporate a significant amount of intuition. The treatment in this paper is cast in terms of sampling theory and trigonometric interpolation. Under this viewpoint, the effects of devices such as digital frequency dividers and pulse-count discriminators are quite easy to understand, and the enhanced noise immunity associated with bandwidth expansion can be interpreted in terms of diversity reception.