But I wonder (always dangerous), if operating on some of the noisier bands,
would there be a benefit to using a narrower filter to cut down on the
amount of energy hitting the DSP in order to help with digging out weak
signals? Or is that not a consideration with this particular implementation
of DSP in the K3?

In general, the DSP can handle signals and noise below about S9+40 or so without undesired effects. Signals between about S9+40 and S9+60 will start to activate the hardware AGC (to protect the analog to digital converter from overload), so if there are strong signals inside the roofing filter passband but outside the DSP IF filter passband, they can make their presence known by activating (or "pumping") the AGC.

So, it isn't the weak signals or noise that are of concern, but the presence of adjacent signals that are (a) stronger than the one you are trying to copy and (b) above the hardware AGC threshold.

Contests -- and therefore weekends -- come to mind :-)

73,

Lyle KK7P

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