[time-nuts] Finally, Success

Bob Stewart bob at evoria.net
Mon Sep 15 12:23:28 EDT 2014

My daughter and I were discussing what she does for a living with time and phase as a geophysicist and relating that to what I'm trying to do with my GPSDOengine.  I explained that I was trying to keep the frequency accurate and stable, while also keeping the phase near a target of 180 degrees.  And suddenly, I realized that that's not what I was actually doing.  For the "I" term of PID, I was integrating on phase position, which was never going to work.

So, I made a change to start integrating on the phase change from second to second (i.e. frequency error), and I think this is finally performing correctly.  The DAC is now very flat, and the phase is moving around as would be expected from Bob's and Tom's comments on the LEA-6T.  Here's an ADEV of the GPSDO's OCXO vs the 10811 in my 5335A.  It covers a timeframe from about 11:00PM last night to about 11:00AM this morning.  This is with the PID running as a PI controller with very small P and I gain values.


Bob - AE6RV

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