[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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