Thanks Jerry,
You beat me to the explanation. ?The OP mentioned a menu routine we (TSW) had in some of our early firmware but we removed it after we discovered it essentially made no difference. ?We just set it to a compromise 10pF and left it there. ?
Start up drift is so minimal it isn¡¯t even worth spending time messing with it.
Jim, W0EB
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On May 17, 2021, at 3:29 PM, Jerry Gaffke via groups.io <jgaffke@...> wrote:
?
Best to leave it at 8pF, though it doesn't really matter.
Quartz crystals are cut for a parallel resonance that assumes some stray parallel capacitance
due to traces and device pins.? They typically assume around 18pF.
The Raduino board layout might add a couple pF, but not enough to get that up to 18pF.
For this reason the 25mhz reference oscillator is typically about 150khz too high.
This is easily compensated for by the calibration procedure, which adjusts the value of si5351bx_vcoa
Jerry, KE7ER
On Mon, May 17, 2021 at 09:57 AM, Gerard wrote:
I stumbled upon this document. Simple curiosity of choice of capacitance of the crystal master
See appendix B:
Turn the uBITX on and as soon as the Splash Screen (Banner) appears, press and hold the Encoder/Function button until ¡°Alignment¡± appears. Immediately release the button. XTAL (6, 8 or 10pF) will appear along with "push to set". Using the encoder select the load capacitance of the master crystal on your Raduino. The default is usually 8 pF if it¡¯s a factory Raduino card. If you don¡¯t know the master crystal¡¯s load capacitance, assume 8 pF and just press the encoder button to set.?
My questions:
This means that Arduino can have a different capacitance?
How do we find his?
In the software of KD8CEC is it stated somewhere?
Simply for curiosity
cdt
Jim Sheldon