The 5390A Frequency Stability Analyzer will characterize oscillator stability in either the time domain or the frequency domain. For time domain characterization, the unit measures fractional frequency deviation which represents the RMS deviation of the signal from the nominal carrier frequency measured over a given time interval. For characterization in the frequency domain, the unit presents results in terms of the spectral density of phase fluctuations. The instrument specializes in high resolution phase noise measurements close to the carrier where other techniques are difficult to use or are unable to make measurements at all. The system can accomodate a wide frequency range of input signals from 500kHz to 18GHz.