EMRFD Message Archive 15037
Message Date From Subject 15037 2018-09-05 12:04:08 kb1gmx Si5351 crosstalk between outputs
Did some testing today as I was going to put a 5351 in an Atlas 210 and use software to
switch BFO and VFO rather than the existing FET switch....
Hard stop on that. I"m gong back to the crystal oscillator.
Reason THe SI5351 if you run two or more VFOs the crosstalk is about -58DB.
Again differently, if you use a 5351 for two or more oscillators the signal from
the other two will appear as a signal -58db down from the oscillator in use.
I first saw this in uBitx. Figured it was layout issue but testing it with several
obtainable 5351 boards I got the same result hooked to nothing.
Test is simple pick three frequencies that are distinct and non-harmonic
look at any one with SA. note the spectra clean and has harmonics (its a
square wave so ok). Now load any of the reamaining two oscillators and bingo
you now have a spur at that frequency about 58DB down. Worse for all 3.
Also I tried a 100ohm load, slightly better (2db) but threre. At 240ohms its nearly
-70db down the measure output.
This means for best crosstalk one must very lightly load the output.
That makes its output about as good as a 9851, and people moan about the SFDR
being 60 or 70db.
15038 2018-09-05 12:22:39 Dana Myers Re: Si5351 crosstalk between outputs 15039 2018-09-05 12:52:35 Tayloe, Dan (Noki... Re: Si5351 crosstalk between outputs
Since a 5351 only cost $1 each, why not just use two?