Forum Administrator wrote on May 14th, 2012, 1:01am:Frequency is the instantaneous derivative of phase, so if there is noise in the phase then there is noise in the frequency. Since they are so closely related, you are free to use either to describe your situation. As to why the term phase noise is more common that frequency noise, I am not sure. It is likely historical. It is clearly an electrical engineering convention. I have mentioned it to physicists occasionally, and they are largely unfamiliar with the term but very familiar with the phenomenon. They generally refer to phase noise in oscillators as linewidth.
-Ken
The "phase noise" term got glued to this based upon the use of PLL's in the timing recovery process.
(disk drives, modem's and other comm signal processing stuff) - the "phase relationship" between data and PLL clock and eye diagrams caused that .
The "line width" term (have not heard that one in a long time) I believe comes from looking at spectral spreading of a single tone on a spectrum analyzer.