# [time-nuts] Upper limit on phase noise from two oscillators.

Mike Feher mfeher at eozinc.com
Wed Apr 27 11:47:23 EDT 2005

```This does not seem to make sense. No matter what you are measuring it is
assumed that the phase noise of the item being measured is greater than the
piece of test equipment doing the measurement, else you would not see it. In
other words, if it is a spectrum analyzer, then the noise floor of the
analyzer has to be less than that of the individual oscillators being
measured. So, if that is the case, there is no reason why the oscillator's
phase noise cannot be measured directly and then which one is better can be
readily determined. If mixing two oscillators together to use the mixer as
the phase detector, would mean that the measurements would be made near DC.
In the direct measurement, the measurement will be made at 10 MHz, no
difference in the spectrum analyzers performance either way. Although as I
mentioned before more often than not a good oscillator's phase noise is
better than that of the instrument used, hence it is easier to make the
measurement after multiplying the UUT up to a higher frequency like 1000 MHz
and then using the mixer method. - Mike  -

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Jeffrey Pawlan
Sent: Wednesday, April 27, 2005 11:20 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Upper limit on phase noise from two oscillators.

Yes, the upper limit will be one of your oscillators and it is not possible
to
know which one. When you have actually made the measurements, don't forget
to
subtract 3dB from the reading because the noise contribution of the two
oscillators is power-additive being non-coherent to each other.

73,

Jeffrey Pawlan, WA6KBL

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