Greetings All.
Maybe I can add a tiny bit of information to this discussion. Back when we
started ADSL with the HDSL work in 1987 we quickly learned that the UK had
a special problem (through the work of British Telecom) because of the very
wide use of QUAD wire in the distribution plant. QUAD was four wires twist
wound uniformly together rather than two pairs, each twisted independently.
This caused the much modified ISDN (2B1Q and 4B3Q codes) based HDSL/ADSL
and the multi tone modes (now almost the universal way to go) to have a
special lower bit rate option for use in the UK. I was able today to find
one of the current popular ADSL chip sets, in this case a multi tone type,
and I see a four pins out of well over a hundred that "implement the UK
option" so this must still be an issue in the UK.
At the end of the day, this means the UK will have a large extra power
bulge at the very low frequencies. Beyond this, there were tests done in
1990 that showed the proposed 2B1Q and multi tone models would not reach
any where close to the range on UK QUAD wiring.
One final point, if you doing the ADSL setup yourself. The North American
ADSL/HDSL systems are largely line powered. It takes a major effort to
deliver 1W of DC to the far end of a long local loop so they regularly see
both sides of the 120VDC office battery for a total of nearly 250 V DC on
the loop from the central office. This can cause some very strong
reactions when ones fingers get into the stuff so if your doing it yourself
it is best to be careful, many of us have forgotten how to live with higher
voltages with all this 5 and 12 v stuff hi.
Good Luck....
Larry
VA3LK
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