[Elecraft] K3: DSP filter steps; am I wrong?

[Don Wilhelm]

Doug,

I believe you are correct.  I would also believe that most of the 
requests are coming from users who are attempting to use HI CUT and LO 
CUT at narrow bandwidths.
What you say is correct if one uses the WIDTH control - the center 
filter frequency stays the same as the width is reduced, and if the 
desired signal is centered in the passband, the QRM will be reduced 25 
Hz on each side.

OTOH, the SHIFT also moves in 50 Hz increments, so there is some 
validity in asking for a reduction of the step size for the shift 
control - shift can easily force one off the edge of a narrow filter.  
But when the filter width gets less than 250 or 200 Hz, I can see little 
use of the SHIFT knob anyway, but that is my personal opinion, others 
may differ.

So if one is using the HI CUT and LO CUT when operating at CW 
bandwidths, I suggest using WIDTH instead.  Similarly on SSB, it is 
prudent to use only the HI CUT and LO CUT to maintain intelligibility 
while cutting out QRM.  On SSB, the high end can be cut drastically, but 
the low end cannot be cut too much or intelligibility will suffer.  With 
care, one could use a LO CUT up to about 350 Hz, but to my ears, 400 Hz 
or more of LO CUT will turn an acceptable SSB signal into garbage.

73,
Don W3FPR

DOUGLAS ZWIEBEL wrote:
> HI all...
>
> I really wonder why there is so much discussion about the filter step
> size, which is currently 50hz.  Maybe I am just nuts, but doesn't that
> 50 hz "come off" of each side of the BW?
>
> Here is what I imagine...
>
> I am on frequency A with a DSP filter BW of (say) 500 (lets ignore the
> roofing filter for now) and I hear a little QRM a bit above me.  When
> I crank the DSP down to 450, isn't that moving the "leading edge" only
> 25 hz (and also the trailing edge).  So in reality, am I not
> "changing" things in 25hz steps in terms of the offending QRM?   Is
> there really a situation where you would need to narrow it 12hz
> instead of 25hz (and appreciate the difference)?
>
>