[time-nuts] OCXO and fluctuations after EFC adjustment

[Taka Kamiya]

Funny you should mention this.
During testing, I noticed an odd repetitive and modulated signal on ALL DC lines.  It looked like a typical AM modulated signal of 100KHz carrier and somewhere around 1KHz signal.  It was around 40mV p-p.

Long story short, it was the oscilloscope probe that was picking up the signal.  Different scope and different probe showed there are no such signal on any of my power lines.

--------------------------------------- 
(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG
 

    On Saturday, April 11, 2020, 12:56:26 PM EDT, Joseph Gwinn <joegwinn at comcast.net> wrote:  
 
 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

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