[Elecraft] DSP and the K2 (was Comparing the K2 to other RIGs)

[Dave White]

Bob, N7XY asked for more comments regarding using an outboard DSP with
the K2.  I have used two such units; the TimeWave 599ZX (latest
firmware) and the ClearSpeech Base II.  My K2 is fully loaded, including
the K2 audio filter (KAF2), and all of the "latest" mods from the
reflector (at least on the receiver end). My operation is strictly SSB
or digital modes.

As background, I am a big fan of DSPs, especially when I used them with
my previous rigs (assorted "high end" units).   When used with the K2, I
have tried both units using the external speaker output from the K2, as
well as tapping the 599ZX into the audio cct after the KAF2 audio filter
(to provide more constant audio level feed -- I built a special
interface board for this to convert the signal from "balanced feed to
unbalanced" and back again -- I was careful to match audio levels and
impedances so as not to overdrive the K2 final audio amp). 

My experience with a DSP on the K2 have been somewhat disappointing (ie:
the improvement in audio and reduction in noise was less dramatic than
anticipated). After months of careful listening, I came to the
conclusion that the receiver of the K2 was quieter than previous rigs
and hence DSP filtering improvements were marginal.  I did not use the
bandwidth reduction controls on the 599ZX very much, as I always seemed
to be able to reduce adjacent channel interference using a combination
of IF filter adjustments on the K2 (the preferred method).

The one major advantage to either DSP has been the automatic heterodyne
reduction feature, something the K2 lacks. Both DSP units perform this
function well.

At this point I prefer the ClearSpeech Base II for it's simple operation
and lower cost. On the noise reduction side, the time constant averaging
feature of the ClearSpeech algorithms take longer to respond than the
599ZX, but the effect is not objectionable, and simple rewiring of the
input feed cct to the ClearSpeech may eliminate some of this effect; the
ClearSpeech On/Off switch turns the unit off as well as bypassing the
audio -- my thought is to retain power and audio feed to the input while
switching the audio output only, hence leaving the noise reduction cct
active and the noise reduction algorithms "up to date". I also found the
ClearSpeech noise reduction less aggressive than the TimeWave, which, in
my opinion, was better suited to the K2's lower receiver noise (and yes,
I know the TimeWave noise reduction effect can be adjusted).

Another advantage for the more adventurous is the ability to mount the
ClearSpeech board into an EC-2 with a pair of K2 speakers to make a
matching DSP'd external speaker enclosure.  I prefer to have a front
firing speaker in my shack. This is my next project.

My comments on the KAF2 echo those of others on the reflector; I find
the overall effect of KAF2 cct in reducing high frequency noise an
advantage.  However, I make limited use of the other audio filter
functions as they are designed primarily for CW mode.  They have proved
an advantage on occasion with digital modes; it depends on the nature of
the interference. Has anyone experimented with altering the
characteristics of the KAF2 filters to make them more suitable for
broadband (SSB) work?  My filter design skills are weak.

Anyway, I now have a TimeWave 599ZX for sale ;-)

As always, the experiences of others may be different depending on their
operating preferences and opinion as to what constitutes "good received
audio".

Regards

Dave White
VE6DRW
K2 S/N 2171