[time-nuts] FE-5680A tuning vs resonant peaks

[gandalfg8 at aol.com]

Hmmm...
You mention varying suply voltage by 1.5V, but from where as a starting point?

It's been a while since I calibrated an FE5680A but looking back through my notes, doing it "properly" is, or was for me anyway, a non trivial exercise.I'm not familiar with the Windows software mentioned but the approach I remember was first to determine what, if any, offset was programmed into the unit as received, then to measure the frequency of the unit as received, then to calibrate the tuning itself by setting positive and negative tuning extremes and measuring the frequency range before interpolating to find an initial tuning word, followed by calculating a further approximation, and so on and so fifth, and of course eventually programming the FE5680A accordingly.

At that time I was using a similar test setup of a 53132A referenced to a Thunderbolt, although I did use a second Thunderbolt feeding the second channel of the 53132A as a confidence check.
Much as I love Lady Heather, hmmm just how kinky is that?:-), I don't rely too much on her reported offsets etc, preferring to trust hardware measurement for that, but would suggest that if she is showing your thunderbolt as locked and tracking a reasonable number of sats then experience suggests you should be able to trust your Thunderbolt as being on frequency.
Experience also suggests, at least with all the units I've seen, that the FE5680A generally reached the surplus market with a programmed offset of zero, presumably because that was good enough for its intended purpose.Soooo, I would suggest that if you have any doubts at all the first obvious thing to do is to reprogram the offset to zero, and start again from there.
I'd be happy to share my programming notes, but must admit I'm having a bit of fun understanding them myself right now:-)

Nigel GM8PZR