Well, I ran a test this morning. With a shorting plug on the input SMA connector and running it from a battery pack via the USB port (no PC interference) I saw no spurs anywhere around 70MHz.
But I seem to have another problem; at least at low RBW settings. Look what's happening at ~46MHz, which happens to be where the LO switches from low band to high band. It looks like the LO may stop working sometimes. With a 100MHz range and AUTO RBW, I can see the harmonics from the reference output at 10, 60 and 90, so this is happening intermittently.
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John P.
WA2FZW
John P