On 3/1/15 10:23 AM, Joseph Gwinn wrote:
time-nuts Digest, Vol 128, Issue 1, Message: 8
Date: Sat, 28 Feb 2015 17:46:18 -0800
From: Jim Lux <jim...@earthlink.net>
To: Discussion of precise time and frequency measurement
<time-nuts@febo.com>
Subject: [time-nuts] simple explanation of noise spectra with mixing,
etc.
Message-ID: <54f26f6a.6030...@earthlink.net>
Content-Type: text/plain; charset=utf-8; format=flowed
Is there a handy "one pager" kind of explanation of noise spectra after
some forms of signal processing..
The best source for the math is probably Fred Walls:
F. L. Walls, “Correlation between upper and lower sidebands” IEEE
Trans. UFFC, Vol. 47, pp 407-410, 2000.
"PM and AM Noise of Combined Signal Sources", Fred L. Walls, Total
Frequency, fredlwa...@cs.com, Proceedings of the 2003 IEEE
International Frequency Control Symposium and PDA Exhibition Jointly
with the 17th European Frequency and Time Forum,
0-7803-7688-9/03/$17.00 © 2003 IEEE, pages 532-540.
I'll look those up..
I was hoping that someone, somewhere had done a "guide to phase noise"
in 1 or 2 pages or a poster.
There's lots of pieces scattered hither and yon, but before I spent much
time generating my own..
Kind of like that cool plot that a time-nut has which shows the spectra
and allan dev of the various colors of noise in a table.
For instance, if you have a oscillator which has a 1/f characteristic,
and you mix it with itself, what is the spectra of the output of the mixer.
Mixing is a multiplicative process, so this is equivalent to squatting
the signal, which doubles its frequency, so the effect will be 20
Log10(2)= 6 db increase of phase noise on the double-frequency terms.
I assume you mean squaring..
True, the "2 f" term will have 6dB more.. But what about the baseband/DC
component..
Your bottom-line question will be if there is any cancellation of phase
noise; this will involve the time delay for the rata signal to get to
the target and return. My guess is that there will be no
cancellation.
Short ranges (<1 km) so actually, lots of cancellation. the round trip
delay is 6 microseconds, so a variation at, say, 10 Hz, is pretty well
cancelled out.
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