A note on signal-to-noise ratio in band-pass limiters

A simplified analysis is presented to explain physically the change of signal-to-interference ratio which occurs in a band-pass limiter. The analysis utilizes the concept of sideband resolution into symmetric and anti-symmetric parts and considers only the asymptotic case where the signal-to-interference ratio is small in comparison with unity. Wide-band correlation-detection systems are discussed, as well as ordinary band-pass systems. The important conclusion is reached that the degradation is highly dependent on the statistics of the interference amplitude fluctuations. However, when the signal is weak compared to the interference, the maximum possible degradation is 6 db and occurs for constant-amplitude interference. Degradation with noise interference in a wide-band correlation-detection system has been obtained for arbitrary signal and noise bandwidths. It is found that the degradation ranges between 0.6 db and 1.0 db, the latter figure being for the case where the signal bandwidth is greater than approximately three times the noise bandwidth.