Re: Reference Frequency Instability?

Arv Evans <arvid.evans@...>

If the frequency shift is an exact amount with that amount being repetitive then
it would seem that software might be the culprit.  Reloading the software may
be necessary.

If the frequency shift is not an exact repetition of the prior shift then it may be
due to frequency drift in the 27 MHz crystal.  Try adding a small heat sink to
the 27 MHz crystal. 

Arv  K7HKL

On Sat, Apr 28, 2018 at 5:27 AM, Alan G4ZFQ <alan4alan@...> wrote:
I realised my tx frequency had moved up 22Khz. I switched off/on and tried again and saw the tx frequency had now moved up 44Khz. After recalibration the same result reoccurred. I switched to VFO B and found it had not moved from 7.030 so I switched off/on and found tx now on 7.052. A repeat off/on brought VFO B up to 7.074.
There don't appear to be any dry solder joins but I retouched the 27 Mhz xtal pads to make sure but the QCX performance is unaltered.


Presumably the 27MHz Xtal is unstable. Can you confirm that with a RX?
If so there is little you can do except trying a replacement.

If you are really adventurous the Si5351 data sheet says "6.4. External Crystal Load Capacitors
The Si5351 provides the option of using internal and external crystal load capacitors. If internal load capacitance is
insufficient, capacitors of value < 2 pF may be used to increased equivalent load capacitance. If external load
capacitors are used, they should be placed as close to the XA/XB pads as possible. See AN554 for more details."  But maybe that's a daft suggestion and might not work anyway:-)

I had the problem with my U3S 10 27MHz Xtals were 99p on Ebay...

73 Alan G4ZFQ

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