[time-nuts] Phase noise measurements - getting started.

Mike Feher mfeher at eozinc.com
Sun Apr 24 10:43:00 EDT 2005

One thing you may consider is multiplying your source and reference up to a
much higher frequency and then mixing them together, using the mixer as a
phase detector, to a low frequency for measurement. Problem being is that
the phase noise of most modern oscillators, somewhat removed from the
carrier, is way way down and most often below the noise floor of the
instrument used to try ad measure it. Of course another question is where
does the carrier stop and the noise starts? Naturally it all depends on the
intended application. Keep in mind the 20*log(N)factor. So, if you take a 10
MHz oscillator and multiply it to 1 GHz the phase noise will have increased
by 40 dB/Hz, a much easier to measure number. Of course you do have to be
careful to make sure that the noise contribution of your multipliers is
minimal, and, fortunately it usually is. 73 - Mike

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of David Kirkby
Sent: Sunday, April 24, 2005 9:53 AM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Phase noise measurements - getting started.

How is the best way to make phase noise measurements, starting from 
limited test kit?

Methods I've seen rely on a low noise oscillator - not a lot of use if 
you don't know the noise performance of any of your oscillators. Another 
assumes your two oscillators each contribute the same amount of noise, 
which is probably not true on old oscillators, even if they are the same 

A third seems a bit more promising - the use of 3 oscillators and 
solving a set of simultaneous equations. I've not looked at the maths of 
this, but assume that it will not work too well if two oscillators are 
quite good, and a third bad.

I should soon have a 5370B time interval counter with its own 
oscillator, plus an oscillator I want to test. I also have access to a 8 
or so year old spectrum analyser (never recalibrated), scopes, mixers, 
lock-in amplifiers and general lab kit.

My pocket money does not quite stretch to the latest all singing all 
dancing kit from Agilent.

Dr. David Kirkby,

Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/

time-nuts mailing list
time-nuts at febo.com

More information about the time-nuts mailing list