Editing Phase noise (section)

==Measurement==
Phase noise can be measured using a [[spectrum analyzer]] if the phase noise of the [[device under test]] (DUT) is large with respect to the spectrum analyzer's [[local oscillator]]. Care should be taken that observed values are due to the measured signal and not the shape factor of the spectrum analyzer's filters. Spectrum analyzer based measurement can show the phase-noise power over many decades of frequency; e.g., 1&nbsp;Hz to 10&nbsp;MHz.  The slope with offset frequency in various offset frequency regions can provide clues as to the source of the noise; e.g., low frequency [[flicker noise]] decreasing at 30&nbsp;dB per decade (= 9&nbsp;dB per octave).<ref>{{Citation |last=Cerda |first=Ramon M. |title=Impact of ultralow phase noise oscillators on system performance |date=July 2006 |journal=[[RF Design]] |pages=28&ndash;34 |url=http://rfdesign.com/mag/607RFDF2.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://rfdesign.com/mag/607RFDF2.pdf |archive-date=2022-10-09 |url-status=live }}</ref>

Phase noise measurement systems are alternatives to spectrum analyzers. These systems may use internal and external references and allow measurement of both residual (additive) and absolute noise.  Additionally, these systems can make low-noise, close-to-the-carrier, measurements.