On Jun 19, 2007, at 1:08 AM, Julian G4ILO wrote:
On 6/18/07, Toby Deinhardt <[EMAIL PROTECTED]> wrote:
It has always struck me as a bit silly to go from analog to
digital back
to analog only to return to digital, which is what you would be doing
with the K3 and a sound card based solution.
I think the number of conversions is the same, it's just a matter of
whether the conversion is done in the computer or the radio. Since a
computer has a more powerful processor, I would expect it to do a
better job, if available. The value of the built-in encoder/decoder is
to allow operation using popular data modes *without* a computer.
Not true. The K3 converts from A:D as a step in the second IF. The
final filtering takes place in the K3's DSP as does the demodulation.
Don't be fooled: all the modules are still there. It is just that
some of those modular functions are now performed in digitally in
DSP. If you draw all the functional blocks, e.g. gain, filter, mixer,
oscillator, they are all still there in DSP.
If you then go to a soundcard you are now adding another conversion
and a third IF. The K3's second IF (DSP) does its conversion and
filtering but then does a conversion to a third IF, including a
conversion from digital back to analog. We tend think of this as
audio but it really is not. It is a third IF with no control over the
AGC. The final amplification, filtering, and demodulation now takes
place in the computer's DSP.
Let me put it another way: one of the reasons that the Elecraft
receivers work so well is that they do fewer conversions and use
lower IF frequencies so that they can put good filtering as far
forward in the chain as possible. This gets rid of products that
could cause IMD in later stages. (The IMD may still be present in the
stage but if you get rid of one of the offending signals you won't
experience the IMD.) What you are suggesting is that we negate one of
the advantages that Elecraft has built into the radio. This seems
silly to me.
My interest in radio is data communications. It may just be the
equivalent of instant messaging, e.g. PSK31, or it may be something
more complex, e.g. IP over PACTOR-III (OFDM). The K3 is [almost]
unique in its ability to do the demodulation in its DSP and have that
process optimally coordinate with the rest of the stages in the
radio, i.e. it will do the best possible job with the signal.
Frankly, I wouldn't want to give that up. I want a whole boatload of
demodulators there in the K3's DSP with access coming out to me in
some convenient fashion -- like on an ethernet connector. (Sorry, I
just couldn't resist. :-)
73 de Brian, WB6RQN
Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com
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