KAF2 v. KDSP2

[Bill W4ZV]

W1WF wrote:
 >The question is, why would you want to have the KAF2 instead of the KDSP2?

         Cost, and for some issues the KAF2 will work as well as its
more expensive brother.  Many guys have KAF2's sitting in their
desks that have been replaced by KDSP2's, and these are typically
available for $50 or less (some even give them away).  This is
versus $219 for the KDSP2, which is a fair increment to the K2's
base price.

         I first built and used my K2 without any audio filter, because my
experience has been that they did not do much for me (and I've tried
almost every audio filter there is including DSP, SCAF and the Hildreth
filter described by W6NRW in a January 1980 Ham Radio article).  Part
of this has to do with how you like to listen for weak signals.  I've
found I hear weak signals better with a wider bandwidth than most DSP's
and use the DSP between-my-ears.  The human ear/brain has been proven to
have an effective bandwidth of about 40-50 Hz but it needs a wider BW
input (typically >300 Hz) to process noise floor signals effectively.

         Back to my K2, one night while listening for YA8G (at my noise floor)
on 1814.0, I was quite surprised to hear a signal from W1AW's S9+30
signal sending code practice on 1817.5.  Apparently this was caused by
filter blow-by in the K2's crystal filter.  Eric or Wayne (I forget which)
recommended that either the KAF2 or KDSP2 would clear up the problem.  A
local offered to let me have his KAF2 and indeed it solved the problem
or at least masked it so I no longer hear unwanted QRM from close strong
signals.

         I would first build your K2 without any audio filter and see how you
like it.  You can always add either audio filter later if you decide you
really need one.  If the KAF2 will solve your problem, it much more
cost-effective than the KDSP2.  I seldom use my KAF2 in normal operation
unless I experience blow-by QRM from nearby strong signals when trying
to copy extremely weak signals.  In defense of the K2, this is a corner
case problem that I very rarely notice in normal operations.

                                                         73,  Bill  W4ZV




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[hank k8dd-2]

In the CQ 160 CW contest this past winter we used my K2/100 (SN 850 A)with
the KDSP2.
No receive antenna (that's a whole story by itself!) and an Inverted-L with
a flock of radials.
Probably 80% of the time we ran with out any NR or DSP filters.  If you
could put a dollar
amount on multipliers, the KDSP2 got us about 4 non-North American mults
that we most
likely would not have been 99.9% sure that he was coming back to us without it.
In the month or two after the contest the thing got me another 5 countries
that I probably
would not have heard well enough to work.
Would a KAF2 done that?  Don't know - the other K2/100 (SN 3519 B) has a
KAF2 but no
160M board in it yet, but I don't think so.
That said, I don't like the KDSP2 at all for normal QSO's or HF contesting
(160 is MF), but
it's like that hammer drill I talked the wife into letting me get -- when
you need it to do the
job, you're glad you have it.
And the clock is cute!
73    Hank    K8DD

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[Earl W Cunningham]

I've used both the KAF2 and KDSP2 with my K2 and can offer these
comments:

For the noise reduction feature of DSP to work well requires a wide
bandwidth.  That is why any DSP unit is less effective in the NR
department on CW than it is on SSB.

Personally, I like very narrow BWs when working CW because it enables me
to hear the weak signals better.  The KDSP2 does a very good job in
giving me a very narrow BW with reasonably steep skirts, however that
narrow BW makes its NR feature totally ineffective.  In contrast, when
using the wide BWs necessary for SSB work, the KDSP2's NR feature works
incredibly well.

Comparing the KDSP2 with the KAF2 on CW, I prefer the KDSP2 because I can
set its BW very narrow and therefore dig the weak ones out of the mud
better than I can with the KAF2.

Now, if only my K2/100 had a mu-metal shield around it so that I could
use it with my linear amplifier without degrading its transmit signal
(the hypersil HV xfmr in the amp puts out a BIG electromagnetic field at
60 Hz which puts hum into the PLL oscillator circuit in the K2 unless
they are separated by an unreasonably large distance).

73, de Earl, K6SE
K2 #2622
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