[time-nuts] A silly question ...

Dave B g8kbvdave at googlemail.com
Thu Sep 27 12:55:37 EDT 2018


... Because I'm sure I should be able to figure this out for myself!

I have (as many of you do also) one of the venerable Trimble Thunderbolt
devices.  No problem with that.  All works fine, and is run 24/7, UPS
backup power and all...

I also have (again, as many of you do...) a free running OCXO for 10MHz
used for "other" stuff etc.   Also left running for long periods, but
only when I want to experiment with other stuff and don't want to
disturb what the TB is keeping sane..

Triggering a dual beam 'scope (Tek 465) from the TB on Ch1, and having
the output of the OCXO on Ch2, the resulting display on Ch2 of course
drifts in relation to the static waveform on Ch1.  (Both nice sinusoids.)

If I time how long it takes for the OCXO to drift through one full cycle
(co-incidence to co-incidence) relative to the TB on Ch1, how exactly do
I turn that time, and knowing the base frequency of the TB at 10MHz,
into a ppm discrepancy?

"I think", that if for example, it takes 1 second to drift one cycle,
that works out at 0.1 ppm.   If it takes 2 seconds, it's 0.05 ppm, if it
takes 5 seconds, it's 0.02 ppm etc.   Is that correct?

If not, please feel free to educate me!

As I said, a silly question that I'm sure I would have answered myself a
few decades ago, but age and medication etc...

Interestingly, after "a lot" of googling, I see that anything like this
using "analogue" or "CRT" scopes, has fallen off the radar and the
interweb, and some of the practices using digital oscilloscopes seem to
rely on the instrument itself to make the measurement, rather than from
"observation" and common sense.  (That I seem to lack at times too!)

But I did get diverted into reading up on some of the early history of
CRO's.

Regards to All.

Dave B.

-- 
Created on and sent from a Unix like PC running and using free and open source software.
::




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