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Re: [10GBT] Request for Cat6 Emissions Characteristics



Hi Jose,

What happens if the THP FIR filter coefficients that we exchange are all
ZERO? For instance, you could be operating over a 0m line and/or you could
be working with a PHY vendor that knows how to do tentative decision DFEs -
we know of at least one, don't we? You cannot rely on the THP then.

The data PSD won't help if your frame start PSD keeps shooting up
uncontrollably. I already explained why I used 128 as the frame repetition
rate. If you don't understand that explanation, please feel free to
"correct" my code.

Regards,
Sailesh Rao.
srao@phyten.com

>From: Jose Tellado <JTellado@TERANETICS.COM>
>Reply-To: "IEEE P802.3an" <STDS-802-3-10GBT@listserv.ieee.org>
>To: STDS-802-3-10GBT@listserv.ieee.org
>Subject: Re: [10GBT] Request for Cat6 Emissions Characteristics
>Date: Sun, 25 Jul 2004 18:07:21 -0700
>
>Hi Sailesh,
>
>There are several problems with this code.
>
>1. First of all you forgot to include the data stream, which accounts
>for 99.8% of the PAM12 frame energy. The spectrum you are showing
>corresponds to the remaining 0.2% as Glenn described to you.
>
>2. You made the same mistake as in your rao_1_0704.pdf presentation
>(most slides from 29 to 52). You forgot to include the THP again, which
>was approved unanimously by the task force. The THP will effectively
>whiten the data, so the 0.02dB peaks will likely not be there
>
>3. You increased the duty cycle from 8/5000 to 8/128.
>
>
>If you need further help I can fix these problems for you,
>
>Jose
>
>-----Original Message-----
>From: stds-802-3-10gbt@IEEE.ORG [mailto:stds-802-3-10gbt@IEEE.ORG] On
>Behalf Of sailesh rao
>Sent: Sunday, July 25, 2004 5:39 PM
>To: STDS-802-3-10GBT@LISTSERV.IEEE.ORG
>Subject: Re: [10GBT] Request for Cat6 Emissions Characteristics
>
>Glenn,
>
>OK, I agree with you to keep these e-mails technical in order to advance
>the discussion.
>
>I've written a short matlab code (glenn.m) to illustrate the PAM12 PSD
>problem. I'm using 128 symbols as the repetition rate for the frame
>start symbols in order to keep the vector sizes sane in matlab.
>
>1. Please run glenn(128) and you will see the PSD shape you expect.
>2. Next, please run glenn(65536) and you will see the PSD discretize and
>shoot up by about 50dB because the same pattern is being sent over and
>over.
>
>I hope this clears up the confusion. I think the problem will manifest
>itself in the CISPR average PSD requirements, though I'm not sure of the
>minimum time constant for the averaging. I believe that the FCC only
>uses quasi-peak averaging in our frequency range of interest, but I'm
>not sure what the time constants are there either.
>
>I welcome any inputs from the EMI experts.
>
>Regards,
>Sailesh Rao.
>srao@phyten.com
>
> >From: Glenn Golden <gdg@zplane.com>
> >Reply-To: gdg@zplane.com
> >To: STDS-802-3-10GBT@listserv.ieee.org
> >Subject: Re: [10GBT] Request for Cat6 Emissions Characteristics
> >Date: Sun, 25 Jul 2004 17:33:58 -0600
> >
> >Sailesh Rao writes:
> > >
> > > You are adding these peaky bumps in the PSD to the data "average".
> > >
> >
> >Of course they're adding.  But to assess their effect, it's necessary
> >to account for the duty cycle at which they are being added, which you
> >are not doing.
> >
> > >
> > > This gets worse. A closer reading of tellado_1_0704.pdf reveals that
>
> > > fixed patterns are being sent once every microsecond on all 4 wire
> > > pairs simultaneously!
> > >
> >
> >An even closer reading would reveal that the period is 5 usec, not 1,
> >and an even closer reading than that would reveal that the peak PSD at
> >this rep rate is 23 dB below the data signal level, and consequently
> >irrelevant.
> >
> >The proposed frame alignment signal (FAS) consists of 112 bits out of
> >every 52833. This is represented on each pair with a sequence of 8
> >symbols -- different on each pair, and intentionally synchronized
> >across all 4 pairs -- out a total frame length of 4224 symbols.  Thus,
> >the repetition period is 1/825 MHz * 4224 = 5.12 usec, the rep rate is
> >1/5.12 usec = 195 kHz, and the duty cycle 8/4224, about 0.19%. The
> >power of the FAS is thus
> >
> >     10*log10(8/4224) = -27.2 dB
> >
> >below the steady state power.  The frequency peak of the FAS power
> >spectrum is roughly 4 dB above the average FAS power, hence around
> >23 dB below the data signal. As has Jose and Seki have pointed out,
> >this represents an increment of 0.02 dB above the average power level.
> >
> > >
> > > Talk about peaky PSD bumps in the PAM12 transmit spectra, yikes!
> > >
> >
> >Talk and "yikes!" all you want; it does not affect the arithmetic.
> >At 23 dB below the average signal power, your local FCC/CISPR
> >certification shop would be hard pressed to even detect the presence of
>
> >these "peaky PSD bumps", much less measure them.  If you believe
> >otherwise, then sharpen your pencil and make the case.
> >
> > > I disagree that the "ripple is small". If we keep sending the same
> > > pattern over and over, once every MHz, the ripple won't be small.
> > >
> >
> >I'm not sure I appreciate the units of measurement you're using, but in
>
> >any case, the ripple in the FAS will always be the same size regardless
>
> >of the rep rate: It will be +/- 4 dB relative to the FAS average value.
> >The rep rate determines the average value: 27 dB below the data signal.
> >
> >
> > >
> > > It is technically incorrect to pretend otherwise.
> > >
> > > Heck, I have a good mind to add a large number of dBs to the
>PAM12...
> > >
> >
> >"Yikes!" and "heck" are not technical arguments. Perhaps you would like
>
> >to offer one?
> >
> >
> >Glenn Golden
> >Principal Engineer
> >Teranetics, Inc.
> >ggolden@teranetics.com
>
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