[time-nuts] Re: What's the best HP OCXO for frequency counter reference?

[Bob kb8tq]

Hi

The “typical” 10811 struggles when shut down for a while. Once the oven
is turned off, the boards are just sitting there in whatever environment your
lab provides. Do they soak up humidity or is it something else? We could 
(and have) debated that quite a bit. 

Regardless of what the issue is, the bottom line is that when you turn the beast
back on again, it *might* take quite a while for it to become reasonably good. 
In some cases that means a couple weeks to hit spec limits. In others it might
mean a week or two to get back to “as good as it was”. 

A *good* 10811 will do much better than what the specs would suggest. It may
be a “one in a hundred” sort of item, but they do exist. Ones that barely / don’t 
meet spec (even after a month on power) also exist and they are a lot more common 
than the ones we brag about with various plots. 

What’s the point? Keeping the unit on power is a good idea, even if you have
a good example. Keeping a poor one on power still will not turn it into a good 
one. Checking out the units you have is a “needed thing” before you start counting
on them for this or that. They *all* left the factory a *long* while ago. 

It *does* matter just what you are counting on the OCXO to do. Does phase 
noise at 100 KHz offset matter in your case? Does 10 second ADEV at 5x10^-12 
degrade your performance compared to 5x10^-13? Is drift the only thing that really 
matters? ( and when did you last set it on? :) :) ) If so, temperature stability (in a 
“transport someplace” situation)  likely also matters, testing it is not something 
most are set up to properly do ….

One alternative: Grab a fairly typical telecom Rb. Put a (cheap) cleanup oscillator 
on it. Use that as your “portable” reference. Run it on batteries (or a 12V plug in 
the car)  as you transport this or that item here or there. Let it sit unpowered on 
the shelf until about a week ahead of your planned expedition. 

Fun !!!

Bob

> On Jun 28, 2022, at 9:20 AM, Adrian Godwin via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Related to that ..
> 
> If you use the ovened oscillator for temporary use away from the home
> GPSDO, how good will the oscillator be with those interruptions to power /
> temperature, and will it stabilise during the period you're using it there ?
> 
> I don't know what the vales are, but I'd suggest the option 010 will never
> reach the 001's spec and the 001 may not even be justified.
> 
> 
> 
> On Tue, Jun 28, 2022 at 6:13 PM Dr. David Kirkby via time-nuts <
> time-nuts at lists.febo.com> wrote:
> 
>> I have a 5352B 40 GHz frequency counter which was fitted with a TCXO. I
>> removed that and fitted an HP 10811-60111 S/N 2332A17049 which I removed
>> from a 5370B time interval counter - I have a few of those, and the
>> microwave frequency counter needed the oven more than the time-interval
>> counter.
>> 
>> Looking at the specification of the 5352B, there were 3 oscillator options
>> 
>> * Standard TCXO
>> * Option 001 Oven time based. Long-term aging < 5 x 10^-10 / day after 24
>> hour warmup. < 1 x 10^-7 / year for continuous operation.
>> * Option 010 High stability time base. Long term aging < 1 x 10^-10 / day.
>> < 3.6 x 10^-8 / year for continuous operation.
>> 
>> To be honest, when the instrument is here, I will use a GPS reference. But
>> I might want to take it to the amateur radio club sometimes. I would like
>> to get the best oscillator I can. Are any models going to be better than
>> others, or by this time, is it just pot luck? I think it's the latter, but
>> maybe some are double-ovens and some single.
>> 
>> With the exception of power cuts of up to a few hours, the HP 10811-60111 I
>> fitted has been continuously powered on for a few years. But due to soaring
>> power costs, I am going to switch my ovens off.
>> 
>> Dr David Kirkby Ph.D
>> Email: drkirkby at kirkbymicrowave.co.uk Web:
>> https://www.kirkbymicrowave.co.uk/
>> Kirkby Microwave Ltd (Tel 01621-680100 / +44 1621-680100)
>> Stokes Hall Lodge, Burnham Rd, Chelmsford, Essex, CM3 6DT.
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