Anyway, just let us read both Rob Sherwood and Adam's test data and
use them as a cross reference to each other.
The issue is that Adam's data is flawed in at least two ways. The
notch is wider than the SSB filter which means the noise is not being
applied to the product detector or DSP ADC. Second by reducing the
noise level for DDC receivers, they are not being fairly tested for
the same level of total noise power. There are also questions about
the effects of roofing filters of different bandwidth - to what degree
do they change the total noise power applied to the entire receiver
chain (including the product detector or DSP ADC)? Secondly, what are
the effects of AGC ahead of the product detector/DSP ADC and does the
noise power testing really measure dynamic range or is MDS compromised
by the AGC?
With a 3.3 KHz notch, the only way Adam can fairly test receivers is
with a 6 or 15 KHz roofing filter. If he truly expects to test SSB
performance, the notch width needs to be less than half the width of
the SSB filter. Secondly, receiver MDS needs to be measured with the
noise present to rule out AGC desensitization.
BTW, Adam's MDS measurements for the two K3s he tested are off by
6 to 9 dB compared to both Sherwood and ARRL Labs while his MDS
values for Icom are within 2 dB of ARRL Labs. There is something very
unequal about the testing of the K3.
73,
... Joe, W4TV
On 2015-03-12 9:26 PM, Johnny Siu wrote:
Hello Scott,
I am afraid I do not agree to your comments. I am a owner of both Icom and
entire K-line, I understand what Adam AB4OJ is doing. Adam knows the design
and structure of K3 no worse than any radio expert here (or at least far better
than me).
Anyway, just let us read both Rob Sherwood and Adam's test data and use them as
a cross reference to each other. I don't mind reading articles from different
angles.
While there are many CW guru here, voice mode is still the most popular mode
across the HF users. Some tests under voice mode conditions do give another
view.
I think we just keep our fingers crossed and see what are the results for
IC7851 and K3 new synthesizer model perform in both Adam and Sherwood test.
By the way, both Rob and Adam know each other and do have the chance to
communicate.
73
Johnny VR2XMC
寄件人︰ Scott Manthe <scott.man...@gmail.com>
收件人︰ elecraft@mailman.qth.net
傳送日期︰ 2015年03月13日 (週五) 2:08 AM
主題︰ Re: [Elecraft] Noise Power Ratio and the K3 with new synthesizer?
I suspect that the "Noise Power Ratio" test was used because that is the
only test that Adam could use to get his beloved Icom gear near the top
of the list. Mr. Farson has had a website devoted to Icom gear for many
years, so I'm not sure if this test could be considered even remotely
objective.
Here is a NPR tutorial from another source, for those interested and
technically proficient enough to investigate further.
73,
Scott, N9AA
On 3/12/15 10:53 AM, Chip Stratton wrote:
Adam Farson VA7OJ has an article in the current March/April 2015 QEX
discussing the use of Noise Power Ratio (NPR) to help define a
receiver's performance in a crowded band in a way that might be more
illuminating than the simpler two tone tests. Its an interesting
discussion which makes some sense, but then I'm not anywhere close to
an expert in that field.
In any event, he has figures from a number of transceivers, including
a couple of K3s which no doubt do not have the new synthesizer. The
K3s still performed very well relative the the rest of the field in
these tests, though they were slightly behind the IC-7700, IC-7800,
and TS-590S.
Which of course makes me wonder how the K3 with new synthesizer would
perform in this arena?
>From a guy with a mild metrology addiction...
Chip
AE5KA
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