[time-nuts] OCXO and fluctuations after EFC adjustment

[Joseph Gwinn]

On Sat, 11 Apr 2020 00:24:45 -0400, time-nuts-request at lists.febo.com 
wrote:
Re: time-nuts Digest, Vol 189, Issue 18

> 
> Message: 4
> Date: Fri, 10 Apr 2020 13:23:22 -0400
> From: Bob kb8tq <kb8tq at n1k.org>
> To: Taka Kamiya <tkamiya9 at yahoo.com>, Discussion of precise time and
> 	frequency measurement <time-nuts at lists.febo.com>
> Subject: Re: [time-nuts] OCXO and fluctuations after EFC adjustment
> Message-ID: <99642A49-8CDF-42D4-9039-7A5E7FF23B62 at n1k.org>
> Content-Type: text/plain;	charset=us-ascii
> 
> 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. 

Note that that many DVMs inject noise back into whatever they are 
measuring.  This could be interesting if one is measuring a 
frequency-control voltage.  A RC low pass filter may be useful.

Joe Gwinn