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)?
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