Posted by
Bill Coleman-2 on
Jul 09, 2007; 12:37am
URL: http://elecraft.85.s1.nabble.com/YAQ-Yet-Another-K3-Question-tp449289p449296.html
On Jun 19, 2007, at 9:42 AM, Brian Lloyd wrote:
> 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.
>
> 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.
One way of simplifying this whole process is to move the radio into
the computer. This is in line with a prediction I made way back in
1995 on the CQ-Contest list -- that the radio of the future would be
inside the computer. In 1995, processors were just appearing that had
sufficient DSP capability to do this. 12 years later, it would take a
relatively insignificant portion of the main CPU (or just a portion
of a few cores, as multi-core machines are now common).
What you'd end up with for the "receiver" would be a Mixer and clean
DDS, followed by a high-speed, wide-range A/D converter. Everything
else would be done in the host computer. The "transmitter" would go
the opposite way, a D/A converter followed by a mixer fed by a DDS.
Power amplification could be external to the computer (if the
transceiver were a card).
The interesting part of this approach is that we can re-define what
we mean by a receiver. The detection portion of the radio need not
resolve to the width of an audio channel. Consider a receiver that
can decode every CW signal in a 50 kHz portion of the band.
Simultaneously. How useful would that be?
It also would be good to sell the receiver and transmitters
separately. That way, obtaining the two receiver, one transmitter
configuration needed by SO2R operation could be inexpensively obtained.
Of course, to achieve the IMD and dynamic range of the K3, the mixer
and A/D would be pretty marvelous pieces of equipment.
> 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.
It's still possible to get good IMD characteristics with an up-
conversion general-coverage receiver. There are some $10,000 radios
on the market that do exactly this.
Elecraft has apparently mastered the art of offering high-performance
gear at an excellent price point.
> 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.
Sounds like what you really want is something more like the 1995 pipe
dream.
Bill Coleman, AA4LR, PP-ASEL Mail:
[hidden email]
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901
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