Re: TCXO Behaviour

Robin Szemeti - G1YFG

And as an update, I fitted the "golden" TCXO to the 13cm transverter and it is indeed very stable as described, can't fault it.   I tuned in the Telford beacon when the shed was nice and warm one evening left it running.  It was still the same tone the next morning when the shed was somewhat cooler.  It appears to be excellent, blowing some warm air over it has minimal effect, certainly for SSB purposes, it is more than adequate.


On Sun, 6 Sep 2020 at 16:10, Robin Szemeti - G1YFG via <> wrote:
Noted, thanks for the update. Just need something to tame this very wobbly crystal in the PLL ... I suspect it may be made from cheese.  I'll try one with a block of "something" around it to shield it ... polystyrene or similar.

On Sun, 6 Sep 2020 at 12:44, Andy G4JNT <andy.g4jnt@...> wrote:
I only did a quick test on each.    All seem to hold their frequency quite well to a fraction of a PPM, far better then a straight crystal would.  But some seem to have a long time constant in their compensation.  If you  waft  air over them  the frequency changes rapidly, only by a fraction of a PPM, but sudile (at uWaves) , enough to be annoying.  So if using for  GHz, they do need to be inside a closed container in still air - and definitely away from any cooling fans.

BTW, I encountered one, once that was a frequency hopper.   Sounded like JT4 when multiplied up - those are designed / touted to overcome EMC regs by spreading interference.    Or it may have been digital temperature compensation that was applied via a 4 bit D/A and PRN mod.   If that was the case, it would have been a pretty clever bit of design.

On Sun, 6 Sep 2020 at 00:35, Robin Szemeti - G1YFG <robin@...> wrote:
Out of curiosity, did you test the higher frequency TCXOs and come to any conclusions? 

On Fri, 12 Jun 2020 at 11:48, Andy G4JNT <andy.g4jnt@...> wrote:
I'm using this TCXO 
Part No  
449-LFTVXO075802CUTT     Type  LFTVXO075802Cutt     TCXO  10.0MHz .28ppm
 in my 3.4GHz transverter and for a relative low cost frequency source, it's excellent.  But I can't work out why there is a steady frequency drift from turn-on.  It's only about 0.1ppm so is within spec, and occurs over the first 20 - 30 minutes of operation.

Isn't the whole point of a TCXO that it's temperature compensated ?   Perhaps it's just compensation loop-gain is too low. 

Guess I'm expecting too much :-)

I've just bought a batch of each of the low cost TCXOs that Farnell & RS have available in several different frequencies, 19.2, 26 and 40MHz and will investigate their performance as references.    As modern Fract-N synths prefer a higher Fref than 10MHz,  wondering if these will do, and they can always be locked to 10MHz separately.

Robin Szemeti - G1YFG

Robin Szemeti - G1YFG

Robin Szemeti - G1YFG

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