[Elecraft] Roofing Filters

[Lyle Johnson]

> 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