Measurement of the Capture Effect of Frequency Modulation

Capture Effect is a phenomenon associated with frequency modulation (EM). The capture effect relates the ability of the receiver demodulator to recover the message of the dominant earner when two or more EM carriers of unequal power level are present. In this research, an experimental system is constructed that generates the sum of two EM signals and demodulates thai sum usmg a phase-locked loop (PEL). The effect on capture by several parameters is measured. These parameters are the frequenc\ de\iation of the E.M signal, the frequency of the message, and the lowpass filter design of the PEL demodulator. Capture ratios as small as 0.3S7 dB are observ ed. Results show that the frequency deviation of the stronger signal affects capture. The frequency deviation of the weaker signal has no effect on capture. Frequencies of the messages ha\e small effects on capture.