Minimization of Detection of Baud Rate Spectral Lines by Delay and Multiply Receivers

The detectability of the baud rate of a digitally modulated signal that uses Nyquist pulses is investigated. The intercept receiver is assumed to be a delay and multiply circuit followed by a complex correlator. Since many digital transmission systems use rectangular pulse shapes, Nyquist pulse rate line detectability is considered for receivers optimized for rectangular pulses. For a receiver configuration that is reasonable for rectangular pulses, it is found that with a Nyquist pulse with parameter α = 0.25, the rate line signal-to-noise ratio is down about 20 dB from that for a rectangular pulse signal.