Re: [10GBT] Request for Cat6 Emissions Characteristics
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