[time-nuts] My GPSDO project: OCXO Thermal Oscillation?

Bob Camp lists at rtty.us
Fri Aug 16 15:47:51 UTC 2013


Hi

Ok, let's try some math and see if I can do it without blinking this time….

+/-4 Hz for 6 volts is 0.66 Hz / V
output is 10 MHz so 1 Hz is 0.1 ppm
your OCXO is running at 0.066 ppm / V 
That's also 66 ppb / V

0.02 V at 66 ppb / V is 0.0132 ppb or 13.2 ppt

The UT+ has a sawtooth output that's about 45 ns
That's 45 ppb at one second

5 minutes is 300 seconds

so 45 / 300 = 0.15 ppb or 150 ppt

If it's the later clone version it might be  about 1/2 of that. 

Are you doing sawtooth correction?

Bob

On Aug 16, 2013, at 11:09 AM, Bob Stewart <bob at evoria.net> wrote:

> I'm converting the code for the VE2ZAZ FLL to a PLL.  I'm seeing the phase correction change the EFC up and down about .02V to .03V over a period of 5 minutes or so (it varies).  The full range on the OCXO is about +/- 4Hz varied by 0 to +6V, so at least this is a tiny value.  I feel pretty confident with my code at this point.  I'm using a Trimble 34310-T OCXO for which I've been able to find almost no information.  Could this oscillating phase correction be some sort of thermal oscillation?  I've tried two separate 34310s and both act more or less the same.  My GPS device is normally a UT+, but I just now swapped in an "Adafruit Ultimate GPS Breakout" to the same effect.  Is this good, bad, or indifferent for a GPSDO?  I started this project not knowing what to expect, and I still don't.  Experienced help, speculation, or even just kind words at this point would be appreciated!  =)  I don't have a known good/stable reference to compare this
> to.
> 
> Bob - AE6RV
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