The performance of the amplitude-locked loop with cochannel interference

An improved method of frequency demodulation (FM) is described in which two inband modulated carriers of equal amplitude can be demodulated without causing severe distortion or loss of intelligibility. Essentially, the amplitude-locked loop (ALL) is a high gain, high bandwidth servo-loop similar to a phase-locked loop (PLL) but operating in the amplitude domain rather than the frequency domain. A new approach is taken by the authors which allows the cochannel analogue FM transmissions to receive the digital encoded data at the same carrier amplitude and frequency but without cross modulation distortion or “Rician spikes”. The FM Manchester encoded data communication system with the ALL technology is unique to the authors. The bit error rate (BER) is measured for the normal PLL and ALL demodulation outputs of the FM demodulator at high interference-to-carrier ratio (ICR)