The Detection of Two Modulated Waves Which Differ Slightly in Carrier Frequency

The present paper contains an analysis of the detection of two waves modulated with the same, or with different, audio frequencies and differing in carrier frequency by several cycles or more. Both parabolic and straight line detectors are treated and there are derived the expressions for all of the important audio frequencies present in the output of these detectors when such waves are impressed. There are discussed the types of interference which result when one station is considerably weaker than the other and simple attenuation formulas are employed in estimating the character and extent of the interference areas around the two transmitters. Beyond the use of such formulas no attention is given to phenomena which may occur in the space medium such as fading, diurnal variations in field intensity, etc.