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# Impact of Noise Figure on Phase Noise - RF Cafe Forums

 The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Below are all of the old forum threads, including all the responses to the original posts. -- Amateur Radio -- Antennas-- Circuits & Components-- Systems-- Test & Measurement

 Post subject: Impact of Noise Figure on Phase Noise Posted: Fri Jul 22, 2005 3:03 pm
Lets say you have a signal at a known frequency with a known amount of phase noise, and you pass the signal through a fixed attenuator, is there a way to calculate/estimate what impact the attenuation has on the phase noise of the output signal?

 Post subject: Posted: Sun Jul 24, 2005 11:30 am

Joined: Sun Aug 03, 2003 2:02 pm
Posts: 653
Location: Erie, PA
 Greetings crg:My guess is that the effect of the attenuator on phase noise would be similar to the intended signal and noise. You would need to perform a cascade analysis for the path where the phase noise is first injected and treat that component of the total signal as a separate signal that is summed with the intended signal. The discrete phase noise component would be attenuated by an amount equal to the total Gain in the path from the phase noise injection point and the continuous phase noise component would be subject to the total Gain and Noise Figure.If the phase noise is present on the signal at the system input, then it is treated to the same effects as the rest of the intended signal and noise.If it is injected in an LO at a mixer, then the phase noise component is determined by a separate cascade comprised by the path the LO signal takes.In the last case, for a real system the summation of the two components [(intended signal + noise] + [LO + phase noise)] would be a point-by-point vector addition, so a simple scalar summing could produce erroneous results.Any comments by others? _________________- Kirt Blattenberger RF Cafe Progenitor & Webmaster

Posted  11/12/2012