EMRFD Message Archive 12728

Message Date From Subject
12728 2016-04-23 16:36:51 Hans Summers Re: Si570 VFO for 210X (was Re: [emrfd] Measured output impedance of

Hi all, Roelof particularly...

I'm sorry Roelof, you did email me a few days ago, and I have not had a chance to reply yet.

Briefly: if you are using the QRP Labs VFO kit http://qrp-labs.com/vfo then yes the Si5351A Synth kit http://qrp-labs.com/synth in that is programmed with even integer multisynth division.

But one point I wanted to make. In the Si5351A the amount of phase noise is very highly dependent on output frequency. E.g. if you have 13.5MHz (the reference is 27MHz) then you will get the best phase noise measurement result since the PLL feedback divider is an integer. If you use 13.499MHz then the phase noise performance will be at its worst.

I am not all that familiar with the Si570 but I think probably the same applies. So in order to properly compare phase noise it would be necessary to do the comparison at a large number of frequencies, I think.

The Si5351A is worse than the Si570, I think the design is a faster PLL loop (faster settling), and the trade-off is a little worse phase noise. The real question as always, is whether the difference in performance is relevant in a particular application. In a receiver for example.

Gwyn G3ZIL uses the Si5351A Synth in a receiver and wrote an article, see http://qrp-labs.com/synth/synthnoise.html comparing the Si5351A LO to a crystal. His conclusion is that the Si5351A is good enough in a receiver.

73 Hans G0UPL

12729 2016-04-23 20:43:41 Dana Myers Re: Si570 VFO for 210X (was Re: [emrfd] Measured output impedance of