[time-nuts] OCXO and fluctuations after EFC adjustment

[Bob kb8tq]

Hi

EFC changes by themselves are pretty much instantaneous. If you are seeing
post tune drift, it likely is from the pot or from things like a temperature change
(or draft) when you go near the part. 

If your grounds are a bit intertwined, the change in oven current will give you
a delta voltage on the ground. That can get into the EFC. Taking care of this 
is harder than it seems. The 10811 has an independent ground return for the 
oven, so it at least is *possible* to do in this case.

A good starting point is to hook up a DVM on your pot. Watch the voltage after
you do a tune adjustment. If the drift you are after is in the parts in 10^-12 range,
that may take a pretty good DVM. 

Tuning adjustments to the coarse tune on the 10811 (or any similar OCXO) are
a different beast. The trimmer cap is heated inside the oven and you will cool
it off a bit doing an adjustment. You can see a bit of post tune drift as a result. 

Bob

> On Apr 10, 2020, at 1:02 PM, Taka Kamiya via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> I have a few HP10811 and was thinking of making an interesting setup:  A setup where frequency is purposely offset by user defined amount by few Hz, and make it selectable.
> 
> Under normal setup, I would use a potentiometer and EFC control the frequency.  When I adjust EFC, the frequency immediately moves but then drifts.  It takes an hour or so to settle down again, then I have to readjust.  Due to precision of my testing setup, I am unable to quantify this.  
> 
> Is this a nature of OCXO in general or is this unique to HP10811?
> 
> --------------------------------------- 
> (Mr.) Taka Kamiya
> KB4EMF / ex JF2DKG
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.