Paul,
I'm curious as to the RF output voltage you're obtaining from your Si5351A VFO.? I suspect you're amplifying for use into the Drake 2NT??
I'm using the same Si board with a homebrew RF voltage amp (images below).? With a bifilar output transformer, it produces 30Vp-p from a +12V source.? That's enough to drive most boatanchor transmitters.
My only issue from these PLL and DDS VFOs is close-in spurs next to the carrier frequency.? They're not nearly as clean as a classic PTO circuit.? I typically see worst-case spurs at -35 dBc.? They're down quite a bit, but it's possible to detect the spurs from stations when propagation is good.?
Paul, W9AC
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Paul Christensen