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Re: [10GBT] Request for Cat6 Emissions Characteristics

On  Thu, 22 Jul 2004 16:07:12 Sanjay Kasturia wrote:
> This makes me doubt the objectivity of your analysis.

On  Thu, 22 Jul 2004 16:52:22  "Kardontchik, Jaime" wrote:
> I would suggest to delete the remark about "objectivity".
> It is really unwarranted.
> Everyone is trying to do the best possible technical analysis
> in real-time.
> It happens that the ones that dare offer their code for public
> scrutiny in order to advance the discussions, end up being
> criticized for the incompletness, inaccuracies, etc, of their code.

I'm not sure that Sanjay's remark had to do with Sailesh's program
having a bug.  Everyone understands that honest mistakes of this sort
will occasionally be made, and that public stonings on the reflector
are not appropriate.  I think Sanjay's remark may have had to do with
what happened after the error was pointed out and corrected.

In his original posting (based on the computations prior to the bug
fix) Sailesh showed four plots: Two large scale, and also two zoomed-in
"EMI PSD" plots. Only the latter two include the 20log(f) radiated
emission frequency dependence, which, in past postings, Sailesh himself
has specifically pointed out as being relevant to EMI considerations.
On those zoomed-in plots, he made a point of noting that the differential
between the PAM8 and PAM12 peaks was trivial:

> In both cases, the peaks for the so-called "EMI PSD"s are within
> 0.01dB of each other for PAM8 and PAM12.

But in the subsequent posting, after the bug was fixed, the zoomed-in
EMI PSD plots with the 20log(f) factor were omitted, and nothing was
said about the relationship between the PAM8 and PAM12 peaks. This
omission was justified with the following dismissive comment:

> Besides, in any case, the FCC limits for emissions increases in
> the neighborhood of 220MHz, thereby rendering Jose's emissions
> contentions completely irrelevant.

and later

> I consider the point Jose made about the emissions issue to be pure
> specmanship, and I've already stated that it is completely irrelevant.

I think Sanjay's response probably had to do with the lack of clear
technical basis with this claim was made, and with the curious way that
plots which had been relevant prior to the bug fix became "totally
irrelevant" after it was corrected, since the actual plots -- had they
been included in the posting -- do not seem to support that contention.

The plots are attached, along with original (erroneous) plots:

    7525_orig.gif          0.75_0.25D filter, original (erroneous) results
    7525_corr.gif                "      "     corrected results

    unger_orig.gif         Ungerboeck filter, original (erroneous) results
    unger_corrected.gif         "       "     corrected results.

These were produced using the original and corrected spectra.m programs
respectively, with changes made only to the axis limits so as to focus
in on the claims being made about the behavior near the peaks.

In the corrected EMI PSD plots -- the ones that incorporate 20log(f)
and were omitted from Sailesh's second posting -- even if one completely
ignores the energy above 216 MHz [I think that's where the actual Part
15 mask breakpoint is] PAM12 has a lower peak value for both filters.
For the Ungerboeck design, both peaks occur below 216 MHz, and the peak
differential -- which Sailesh was interested in pointing out earlier
when his numbers were wrong and showed no penalty for PAM8 -- is now
0.8 dB in favor of PAM12.

So, as far as the actual data at hand goes, it seems disingenuous to use
the step in the EMI mask as justification for dismissing Jose's claim as
"totally irrelevant", when in fact for one of the filters, it supports
exactly the opposite conclusion.

It may well be true that when the smoke clears on this issue, neither
system is significantly different as regards peak EMI.  But the present
data does not make that case, and dismissing it with a verbal flourish
does not help to advance the discussion.

Glenn Golden
Principal Engineer
Teranetics, Inc.