Re: #synth ref frequency #synth

Hans Summers

Hi Alan

27MHz was required for my algorithm to get the WSPR tone spacing exact on 2m. On all lower bands than that, 25MHz or 27MHz both produced exact solutions. Therefore I chose to use the 27MHz crystal in QRP Labs kits. 

26MHz will be fine also, all across HF. Holes in coverage of my algorithm (for exact WSPR tone spacing) only started to appear beyond 40MHz as I recall. So I couldn't say for sure that 26MHz will produce accurate tone spacing for WSPR on 6m, 4m and 2m bands. But you said you used it successfully on 2m so I think it the proof of the pudding is in the eating :-) 

73 Hans G0UPL

On Thu, Feb 28, 2019 at 7:40 PM Alan G4ZFQ <alan4alan@...> wrote:
> somwhere i read about, that the reference clock of the Silab synth in a
> U3S MUST be at 27 MHz.
> But i think, i heard that there is another cause.
> Something with the 1.4648 Hz spacing of the wspr tones ?

Hans has said that a 27MHz is required to make the tones exact.
I do not know if anyone can say what amount of error is permissible with
WSPR but I use a 26MHz TCXO with no apparent disadvantage. (But it is
difficult to be certain, maybe I do get missed sometimes?)
The U3S will operate with a wide range of frequencies, I've tried 10MHz.
But I do not know of anyone  properly testing for signal purity.

73 Alan G4ZFQ

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