Posted by
Bill W4ZV on
Jul 23, 2004; 12:47am
URL: http://elecraft.85.s1.nabble.com/KAF2-v-KDSP2-tp369054.html
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desks that have been replaced by KDSP2's, and these are typically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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