Bicephale
join:2005-09-24
 ·TekSavvy Solutions..
| reply to HiVolt
Re: Stats help from someone at Teksavvy
Spectral Shaping |
HV> Changing the upstream does not affect the
HV> downstream whatsoever, they are on different
HV> frequencies.
I'm sorry but i must express disagreement since it
is possible to demonstrate just the opposite using
a GNet BB0060B MoDem/Router! It's what is refered
to as "Spectral Shaping", i believe, and i suspect
the GNet BB2060 can do the same. Essentially, all
amplifiers generate some noise and that which will
be produced by any MoDem's UpStream signal happens
to contribute locally to the overall noise seen by
its receiver side (e.g., the DownStream signal)...
If one's neighbours can induce Cross-Talk into the
phone line imagine what his own DSL device can do!
Consequently, less UpStream power means less noise
injection and this is what i seem to be observing:
5056/800 Kbps
DownStream Power: 19.59 dB
UpStream Power: 10.95 dB
DownStream Attenuation: 32.0 dB
UpStream Attenuation: 30.0 dB
DownStream SNR Margin: 18.0 dB
UpStream SNR Margin: 7.0 dB
5056/288 Kbps
DownStream Power: 19.44 dB
UpStream Power: 6.36 dB
DownStream Attenuation: 32.0 dB
UpStream Attenuation: 30.0 dB
DownStream SNR Margin: 20.0 dB
UpStream SNR Margin: 6.0 dB
As you may have noticed yourself, it looks like my
DownStream SNR Margin is inversely proportional to
my UpStream Power and it just makes sense to me...
The second reading has been obtained by setting my
UpStream start bin to 8 and my UpStream end bin to
14 while my DownStream start bin was 36 and my end
bin was 248. I've set the Tx Power Attenuation to
-1 dB, Coding Gain was 7 dB. 'DMT' isn't required
to make these tweaks but it simplifies this task a
great deal. A 0.5 dB variation must be considered
inconclusive but it has reached at least 1.5 dB in
this case, points constantly in the same direction
and it's higly reproducible. In conclusion, there
is evidence showing that the DownStream signal can
be affected by changes in the UpStream one indeed!
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