[Elecraft] K3: use of 1.8 filter - clarification

[Guy Olinger K2AV]

That really IS the kicker.  I guess the point is how bad do you want/need
the cost of an extra filter.  How important would it be in the 1% condition
where the signal up or down is INSIDE the roofing filter.

In my experience from home (not the monster antennas out at N4AF), in ANY
phone contest, changing the width from 1.8 to 1.9, thus changing to the 2.7
roofer, always is a large jump in crap inside the DSP.  This is because I
just went from DSP and roofer ALIGNED SKIRTS, that drop 100+ dB in a given
width (combined) to a composite skirt that only drops 50 in the same range.
 This means that the loudness of what is just up and down JUST GOT 50 DB
LOUDER at the roofer change, because the close in skirt is now ONLY DSP
instead of DSP+roofer.

The DSP is great, but hear this, at 400 Hz, the straight selectivity of DSP
plus a CAREFULLY ALIGNED 8 pole roofer is still less than my MP with INRAD
400 Hz 8 pole filters at the 8 and 455 IF slots.

The presumption with no tight filters is that the selectivity of the DSP by
itself is enough.  Personally, my experience is that the K3 DSP, by itself,
as very excellent as it truly is, is NOWHERE near enough to deal with
contests and situations where one is trying to listen to a 0.05 uV signal
next to a 500 or 5000 millivolt signal that is JUST BARELY OUTSIDE the
passband.  It takes the DSP, as excellent as it is, TOO MANY Hz to reach
the ultimate 100 dB.  I need the FASTER DIVING COMBINED skirts of a matched
roofer and DSP skirt to knock off the content just barely up and down.

While my MP has faster diving skirts at 400 Hz using the matched INRADs,
the K3 nearly matches the skirts AND has vastly superior IMD and internal
noise.  ***BUT***  without the matched DSP and roofer skirts, particularly
if the roofer is significantly wider, there will be so much stuff let in by
the missing 50 dB of skirt inside ultimate rejection that the advantages of
the superior IMD are quashed by all the stuff now let in, and in fact, in
that particular situation, the MP would be the superior rig.  Credit where
credit is due.

When I am running at NY4A on 40 with the overwhelming signals from Europe
on the monster quad, I use the 400 roofer and DSP at 450 and the "250"
roofer and DSP at 350 to get sharp aligned hard-diving skirts just above
and below.  Don't bother to tell me that some of those Italian signals are
running anywhere near 1.5 kW because I've rechecked the S meter countless
times, and something that tickles 40 over is an issue.

You COULD say, just reduce the width, and I would agree **IF** it weren't
for so very many people calling fairly well off frequency.  There are times
where I have to reduce the width from 350 to 300 or 250, where the up or
down signal is just too strong and too close and overwhelms the excellent
roofer/DSP combo at 350.  But I know I'm losing contacts.

I know this is more like a NASCAR take on tires, and some of you may be
driving the K3 like the family car.  But if you understand the NASCAR
(severe contest) issues regarding roofer selection, then you know what it's
about and can choose one way or another and know it's right for you without
being snookered.  If you occasionally take the K3 down to the race track
and want it to perform out there, you need to match DSP and roofer skirts,
and align them.

73, Guy.

On Sat, Jan 14, 2012 at 11:43 AM, DOUGLAS ZWIEBEL <dougzzz at gmail.com> wrote:

> But unless you are planning on operating in the
> midst of multiple, super strong signals, then I do not see much "logic" in
> getting a narrower CW filter...and certainly not a narrower SSB filter for
> SSB use.
>