[time-nuts] LTE-Lite module and the pendulum...
SAIDJACK at aol.com
SAIDJACK at aol.com
Tue Oct 21 15:02:52 EDT 2014
Hi John,
while I can't tell you which vendors are affected and which are not (Its
like asking an angler for his secret angling spot :), I can say that most low
cost TCXOs exhibit this behavior, and are thus not really suitable for
GPSDOs.
The ones we used on the LTE-Lite are quite good and do not exhibit this
behavior. They are also 10x more expensive than the lost cost TCXOs in the
exact same package that are typically used in non-critical applications.
So far none of the quite reputable TCXO and OCXO vendors that I contacted
about the problem can explain the behavior to me, like I said they were not
even aware of the issue and had no way to test for it, and I had to prove
it to them by sending our units to them so they can see the issue for
themselves.
Bye,
Said
In a message dated 10/21/2014 11:51:28 Pacific Daylight Time, john at miles.io
writes:
> Great insight thanks. You nailed it: out with the old oscillator and in
with one
> that doesn't have that problem.
>
> Btw the mechanical tuning issue you mentioned is essentially the same
exact
> problem: even the slightest turn will make the frequency jump too high
or too
> low. It can drive you (and the loop) crazy trying to get it on-frequency.
Whenever I've seen this behavior, it has always been caused by uncertainty
or "quantization" on the part of the trimpot's wiper, rather than anything
that could be blamed on the varactor. What would be a good example of a
TCXO or OCXO model that exhibits EFC hysteresis? I don't immediately
understand what could cause this phenomenon, and I'd like to reproduce it here to
see what's happening.
-- john, KE5FX
Miles Design LLC
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