http://elecraft.85.s1.nabble.com/Elecraft-K4-now-in-Rob-Sherwood-s-RX-performance-table-tp7669789p7669791.html
> 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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