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Re: [10GBT] Request for Cat6 Emissions Characteristics

Hi Sailesh,

One item we both agree on is the benefits of power backoff for short
lines. Is 0 m short enough for you?

In your proposal (rao_1_0704.pdf, slide 62) you suggest 10dB of backoff
for lines shorter than 20m. With 10dB of power backoff I don't think we
will have EMI issues.

I don't know of any PHY vendor that has claimed to do DFE tentative
decisions with an LDPC without some tx filter.


-----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 6:32 PM
Subject: 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.

Sailesh Rao.

>From: Jose Tellado <JTellado@TERANETICS.COM>
>Reply-To: "IEEE P802.3an" <>
>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,
>-----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
>Subject: Re: [10GBT] Request for Cat6 Emissions Characteristics
>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.
>Sailesh Rao.
> >From: Glenn Golden <>
> >Reply-To:
> >To:
> >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
> >
> > >
> > > 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
> >The rep rate determines the average value: 27 dB below the data
> >
> >
> > >
> > > It is technically incorrect to pretend otherwise.
> > >
> > > Heck, I have a good mind to add a large number of dBs to the
> > >
> >
> >"Yikes!" and "heck" are not technical arguments. Perhaps you would
> >like
> >to offer one?
> >
> >
> >Glenn Golden
> >Principal Engineer
> >Teranetics, Inc.
> >
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