Improved test methods ease phase-noise measurement

Numerical techniques and the instrumental capabilities available for assessing phase or frequency noise in radar or communications systems are explored. Numerical expressions are defined for the phase noise, spectral density, the total noise energy, and the spectral density of frequency fluctuations. Rough noise estimates can be made by feeding a resonator signal through a spectrum analyzer. A heterodyne counter downconverts the signal to an intermediate frequency where the signal frequency can be repetitively counted and fractional frequencies detected. The heterodyne method is effective for instabilities with periods under 10 msec. A carrier-removal/demodulation technique nulls the carrier and monitors the output with a spectrum analyzer. Other methods described are the delay-line discriminator and phase detector techniques, and error prediction steps are outlined for the latter.