a frequency domain measure of stability and is usually expressed as the SSB spectral density in dBc/Hz. This is the single-sideband noise and is denoted by L(f). It is important in many applications and has direct correlation to the short term stability. Low levels of phase noise are achieved through careful circuit design and use of high-Q resonators. Typically, to measure the phase noise of a crystal oscillator an identical tunable oscillator is used as a reference and phase locked in phase quadrature to the oscillator being tested. This allows removal of the carrier signal while leaving the sidebands to be measured with a low frequency FFT analyzer. If the two oscillators have identical noise, the noise of each oscillator is 3 dB better than that measured for both.
The ratio of the power density of one phase modulation sideband to the total signal. It is usually specified as the single side band (SSB) power density in a 1Hz bandwidth at a specified offset frequency from the carrier. It is measured in dBc/Hz.
The amount of phase noise energy contained in a frequency carrier. Specified in dB/Hz, phase noise amplitude is usually characterized and plotted in 1 Hz increments, offset from the carrier.