On Fri, May 28, 2021 at 1:22 PM BRUCE WW8II <wa8...@gmail.com> wrote:
I LOVE my K3s
Bruce
WW8II
On Fri, May 28, 2021 at 12:31 PM Wayne Burdick <n...@elecraft.com> wrote:
Sherwood has posted his measurements of the K4D's receiver performance in
his table:
http://www.sherweng.com/table.html
We're quite pleased with his test results, which confirm that the K4/K4D
is near the top of its class (direct-sampling SDRs). A K4HD would provide
somewhat higher dynamic range for those stations in extreme signal
environments, but the vast majority of operators will find that the
K4/K4D
more than meets their needs.
I'd like to highlight a few important items in Rob's chart.
First, the K4D has a high 2 and 20 kHz dynamic range value of 101 dB.
Because it's a direct-sampling radio, this figure will hold at nearly all
offsets from strong signals. Second is the block dynamic range number
(128
dB), higher than almost every other "pure" SDR measured. Finally, there's
the LO noise (local oscillator; 148 to 155 dB) -- again, very favorable
compared to all competing SDRs. This is an important number correlated
with
reciprocal mixing dynamic range (RMDR).
Taken together these demonstrate that the K4D will offer excellent
performance in crowded band conditions.
Inevitably a question will arise regarding the chart position of the K4D
relative to a couple of our other transceivers: the K3S and KX3. There's
a
bit of "apples to oranges" in both comparisons.
The K3S uses a superhet receiver architecture. The K4HD will provide a
receive setting that emulates this superhet performance when and if it's
needed. But the "pure" (direct sampling) method used by the K4 (all
models)
has many advantages. One is the elimination of artifacts associated with
crystal filters. Another is that, as a pure SDR, the K4 has a far more
flexible architecture. We'll be able to provide updates to the receive
and
transmit digital signal chains that cannot be added to a superhet like
the
K3S or its competitors.
The KX3 is another Elecraft radio high on Sherwood's chart. Its
performance is excellent, especially at its price point. But its numbers
relative to the K4 are somewhat misleading, as hinted at by Rob's
footnotes. The KX3 uses a quadrature downsampling architecture, which
digitally samples at baseband audio rather than at RF. This is ideal for
a
radio like the KX3 that has to have very low current drain for portable
operations. The K4 uses a direct-samping architecture that requires a
higher power digital signal chain, resulting in important benefits over
quadrature downsampling including much higher and more consistent
opposite
sideband image suppression and 2nd-order intermod rejection. So the two
are
really designed for different applications.
Overall, this first independent test of the K4 validates the performance
of our SDR architecture. Feel free to send us any further performance
questions.
73,
Wayne
N6KR
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