K0WA:
>I do not want to call it an SDR Radio because the technology they
use for detection could be used in a tradition radio) is different
that most radios. I do not want to call it unique because I am not
sure that it is one of a kind.
>We need to look under the hood to see the technology and how that
impacts performance
Excellent post Lee! The Quadrature Sampling Detector
(QSD) scheme used by Flex Radio is not unique to them. In
fact the $11 Softrock40 uses the same type of detector.
QSD has some advantages and disadvantages over the
traditional down-conversion superhet scheme used in K3,
Orion, and most of our older tube rigs like the Drake R4C.
Advantages:
1. Exceptional IMD performance. Limited by the sound
card's dynamic range on the output of the QSD...typically
100-105 dB which is ~10 dB better than the best superhets
(of course I believe this becomes somewhat academic due
to transmitted phase noise and key clicks...even for rigs
with 95 dB IMD like Orion and K3).
2. Wideband spectral display (now up to 192 kHz with the
best of today's sound cards) with exceptional resolution
and dynamic range compared to traditional spectral displays.
Disadvantages:
1. Computer GUI only (i.e. few knobs, etc).
2. Mediocre BDR performance (110-120 dB). Again limited
by the sound card's dynamic range, but here it is 20-30 dB
worse than the best superhets like K3 (preliminary results
showing 143 dB). BDR is important if you are trying to
copy weak signals in the presence of other strong local
signals on the same band, such as you might encounter in
Field Day, duplex single-op contest operation on one band
or in other multi-transmitter environments like contests or
DXpeditions.
The beauty of a hybrid approach (e.g. K3 plus Softrock
QSD plus free SDR software) is that you can have the best of
both worlds. Powerful SDR software plus a wide spectral
display without sacrificing a user-friendly human interface
and BDR performance. This will be very interesting to watch
but I suspect the K3 may significantly impact SDR rigs once
people fully understand what is possible with K3. I believe
it will be much easier (i.e. less expensive) for the K3 to
offer SDR capabilities than vice versa. Time will tell.
73, Bill W4ZV
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