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Calibrating QCX MINI

 

I've read that some folks are offsetting the 27.000 crystal. Is that the right way to go?
 

On 19/03/2024 20:23, KA5HZV@... wrote:
I've read that some folks are offsetting the 27.000 crystal. Is that the right way to go?
I think the answer is in the manual.
The crystal is normally quite a way off nominal.

73 Alan G4ZFQ
 

If you read it in the manual then you¡¯d be right?
 

It's normally not much. I think I set mine to 27.004? or something like that. You can use a known signal source to zero beat. I use WWV when it's in range, but you can also get a good idea by seeing your signal reports on PSK Reporter, or RBN.
--
73, Dan - W2DLC
 

On 20/03/2024 12:55, Daniel Conklin wrote:
It's normally not much. I think I set mine to 27.004
Dan,

With the current QRPLabs TCXO we think in terms of a few Hz. So the old crystals somewhere around 4000Hz off nominal might be considered a long way off:-)

73 Alan G4ZFQ
 

Alan, I should have added some zeros. :) Also, I have the TCXO on mine now too, so I was trying to remember what I did before that.

--
73, Dan - W2DLC
 

Alan? ...? ?Except for Hans' habit of omitting any loading capacitors to maximise output /stability? - but it leaves the frequency rather high
 

Hi Bruce
?
Alan? ...? ?Except for Hans' habit of omitting any loading capacitors to maximise output /stability? - but it leaves the frequency rather high

Not exactly... originally?I had 22pF capacitors from each side of the crystal to ground, on the AVR microcontrollers. I found that there were always a non-trivial percentage of?people?reporting that the unit didn't work, and it was found to be due to the crystal not oscillating; removing the capacitors always solved this problem. So I soon started leaving the capacitors out, which reduced the BOM by two capacitors and had no apparent ill-effect.?

I've left the capacitors out ever after, still with no ill-effect. The crystal tends, as you mentioned, to oscillate a little higher (a few kHz) than its nominal value. But even with the capacitors calibration is still needed. In all the kits we don't need the reference oscillator to be actually on frequency, we just need to know what the reference frequency is. So the capacitors still had no importance.

73 Hans G0UPL

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