[Elecraft] [K3] Filter Cascade Effect

[Ed Muns]

> Right on!  BUT -- one good way to deal with this when you 
> already own the narrower filter is to tell the K3 that its 
> bandwidth is wider than it is. For example, I have tell the 
> K3 my 400 Hz 8 pole filter is 500 Hz, and the 1.8 kHz filter 
> is 2.2 kHz. I find that I also want to shift the 1.8 kHz 
> filter down about 150 Hz. 

I don't think this is a "good way" at all.  Doing this destroys the smooth
consistently incrementing operation of the WIDTH control.  Your actual
bandwidth goes from 600 to 550 to 400, then stays there until the DSP
catches up at 400.  If anything, I'd go the other direction so that the
crystal filter doesn't engage until the DSP is inside it at a narrower
bandwidth.  However, another reason some people do what you suggest is to
modify the passband shape since they prefer the rounder passband shape of
the crystal filter ("softer sound", they say).  I still think that is a
negligible benefit against creating the WIDTH control anomaly.

I agree with Bill that I'd much rather have my roofing filters just outside
the DSP bandwidths I commonly use.  That's why I think it is prudent for K3
owners to forgo additional crystal filters until they've operated the K3 and
found the bandwidths most important to them.  Then, if they really need
nearby strong signal protection for the DSP, they can select wider crystal
filters for their favorite DSP bandwidths.

> Another point -- some have noted that at least some of the 
> roofing filters are actually wider than their nominal value. 

By design, INRAD makes the actual -6 dB bandwidth greater than the filter
name.  See the actual analyzer plots on the Elecraft web site.

73,
Ed - W0YK