[time-nuts] time-nuts equipment verification from scratch (was: WTB: GPSDO)

Attila Kinali attila at kinali.ch
Mon Mar 20 19:23:01 EDT 2017


On Mon, 20 Mar 2017 17:11:36 -0400
"William H. Fite" <omniryx at gmail.com> wrote:

> You are talking about product design, development and optimization, not the
> production of a one-off for home use. Since performance standards are
> already well established, it is only necessary for the developer to test
> the bench built instrument against published standards and determine if
> performance is good enough to suit him. Given a sound understanding of the
> role of various components in the system, it will be a great deal faster
> and easier for the builder to tinker with the one-off then to go through an
> extensive process of model development and verification.
> I have spent a good deal of my career doing performance modeling,
> verification, and validation in collaboration with other scientists and
> also engineers. You describe the process correctly but I think it is
> generous overkill for the topic under discussion here. Or have I missed
> something in the discussion? Is the desired end result a device for
> manufacture and sale? If so, then your approach is right on target.

The question kind of started of from how to verify a GPSDO works correctly.
My answer to that was to use a known-good GPSDO and an vapor cell Rb standard.
Both can be had for quite cheap (<200$ each) or borrowed from a fellow
time-nut. With this and a suitable counter (e.g. PICTIC or TICC) one can
verify the homebew GPSDO quickly and quantify the result.

Chris Albertson injected, that he wanted to do the verification with stuff
he could build on his own, not relying on another GPSDO or "expensive" Rb
standard. I then showed that, while possible to do so, it takes a lot of
effort and time to verify instruments without using known-good references.

Yes, you are right that for Joe Average, this is way overkill. For most
it will be enough to check whether the GPSDO is within 10-20ns of another
GPS (without DO) receiver, and whether the EFC correlates well with the
temperature of the OCXO housing. Both checks can be done relatively quickly,
given access to a counter, a precise thermometer, and a DMM.

But then, this is time-nuts. We love to get the best out of a specific
system... even if it takes more effort than just simply buying better
equipment :-)

			Attila Kinali
You know, the very powerful and the very stupid have one thing in common.
They don't alters their views to fit the facts, they alter the facts to
fit the views, which can be uncomfortable if you happen to be one of the
facts that needs altering.  -- The Doctor

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