[time-nuts] OCXO Phase Noise Measurement in Primitive Conditions

[Bob Stewart]

Hi Poul,

I accidentally replied to only you (and had to repost to the list), so I'm redirecting this thread back to the list.

I have tried smaller gains, but I'll do it again.  I'll post back later with a d gain of 1/9 of what it was for those plots.   The difference will be obvious on the DAC plot.  I did change the differential algorithm since I tried it with low gain, so maybe it'll help.


Bob



________________________________
 From: Poul-Henning Kamp <phk at phk.freebsd.dk>
To: Bob Stewart <bob at evoria.net> 
Sent: Wednesday, August 27, 2014 2:02 PM
Subject: Re: [time-nuts] OCXO Phase Noise Measurement in Primitive Conditions
 

--------
In message <1409165381.1098.YahooMailNeo at web142702.mail.bf1.yahoo.com>, Bob Ste
wart writes:

Your PLL (PID) has (far) to high gain:  You are yanking the EFC around
to every single little wiggle in the GPS signal.

The curve relative to the Rb should be very, very straight, any
wavyness should be on timescales of at least 20-30 minutes, not
within single minutes as your first plot shows it.

This is a very common beginners fault:  I made it myself too :-)

Lower the PID gain, until the DAC/EFC line only wiggles the minimum
amount necessary to keep the OCXO from drifting away from the Rb...




-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
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