K3: DSP filter steps; am I wrong?

[DOUGLAS ZWIEBEL]

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)?

Maybe those requesting a smaller step need it for PSK?  But even then,
it doesn't make a whole lot of sense to me.  How often would adjusting
the DSP bandwidth something less than 25hz (since that is what we have
now), be better than just going to "full" 25hz?  Or viewed from the
other direction, if you want to narrow it even more, narrow it "one
more step" and get really narrow.

If I understand this correctly, great.  But if I don't, please fill me
in because I would genuinely like to find out more.

Thanks!!
de Doug KR2Q
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[Don Wilhelm-4]

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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[Manuel Maseda]

 
Hello,

Can someone tell me if the K3 can be configured for a 1K VFO step size in
SSB mode?

Thanks,
Manuel  W4SSB

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[Don Wilhelm-4]

Manuel,

Yes, set the configuration menu (while in SSB mode) parameter for VFO
CRS to 1.0
Values of 0.1, 1.0, 2.5 and 5 are available for SSB.  VFO CRS is
settable per mode.

After setting VFO CRS to 1.0,  pressing COURSE will toggle between 1.0
kHz steps and 50 Hz steps, but the RATE and FINE buttons interact too
giving a range of steps from 1 Hz to 1 kHz.

Once you make your selections, a bit of practice may be required to take
advantage of all the capability available - but if you only want 1 kHz
steps, all that is needed is to zero the low order digits and press
course and you will traverse the band in even 1 kHz increments.

73,
Don W3FPR

Manuel Maseda wrote:

>  
> Hello,
>
> Can someone tell me if the K3 can be configured for a 1K VFO step size in
> SSB mode?
>
> Thanks,
> Manuel  W4SSB
>
>  

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