Posted by
Bill W4ZV on
Dec 31, 2010; 2:25pm
URL: http://elecraft.85.s1.nabble.com/Re-Latest-Sherwood-table-tp5882563p5882687.html
On Fri, Dec 31, 2010 at 7:42 AM, Bob Naumann <
[hidden email]> wrote:
> Is there a non-engineer's guide to the Sherwood table for those of us who
> are not engineers?
>
> In particular, the table is sorted by Narrow Spaced Dynamic Range, and I
> see
> that the FT5000 is listed first, but the K3 also gets a 101 in that column,
> albeit with a "pf" footnote instead of just an "f".
>
> I decode these footnotes to be "f" = "Measurement was Phase-Noise Limited"
> And "pf" = "Measurement was Phase-Noise Limited" and was "with 200 Hz
> 5-pole
> filter"
>
***Correct on both counts.
>
> OK - so why is the FT5000 at the top of the list? Why no indication of what
> filter was used in the FT5000?
>
***The default assumption is always a 500 Hz filter or the closest that the
manufacturer provides, so ~500 Hz results results are NOT footnoted. The
FT5000 measurements were using its standard 600 Hz filter and the K3 is
footnoted for the 400 Hz and 200 Hz measurements. The K3's 5-pole 500 Hz is
NOT footnoted per the assumed convention.
>
> What is the second sort column for the table? What puts the FT5000 on top?
>
***The sort is by 2 kHz IMDDR3 only. Since the FT5000 achieved 101 dB using
its 600 Hz filter, it is listed above the K3 which achieved 95 dB with a 500
Hz filter.
>
> What does this table really tell us? It seems that both of these receivers
> are pretty close as many of the numbers are similarly different from those
> listed below them.
>
***Yes it tells you that for all practical purposes all of the rigs from
Orion up are practically identical. I doubt you would notice the difference
in 95 dB versus 101 dB in most real world cases.
>
> When a parameter is higher or lower - which is better? I presume that the
> higher the narrow-spaced dynamic range, the better, but what about 100kHz
> blocking (for example). Is higher or lower there better? The K3 is a 140 on
> that one, and the FT5000 is a "lowly" 127. The Down-conversion Kenwood 590
> gets a 144 in this column - is that better or worse than the K3? But, the
> 590 only gets an 88 in the narrow-spaced dynamic range, so I guess that
> means it's much worse?
>
> How does one interpret this data?
>
***Higher blocking (BDR) is better. BDR is important in a multi-transmitter
environment or if you have a very near neighbor. If you had either of these
situations, you might opt for the higher BDR result if the rigs' IMDDR3
results were similar. Phase noise (both TX and RX) is another very
important parameter in multi-transmitter environments (where the K3 also
shines).
Hope this helps! 73 & HNY to all!
Bill W4ZV
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