On Wed, Nov 07, 2001 at 10:54:57AM +0000, Colm Buckley wrote:
> 4", but it's been a very long time since I studied this stuff. ADSL
> works on this principle; it ignores the "large signal" properties of
> the phone line (a simple high-pass filter) and listens only to the FM
> data on the (8MHz?) carrier wave.
See the URLs I referred to the other day. ADSL actually works by
transmitting signals between 1MHz and 15MHz on a large number of smaller
bands - a classic use of FDM to increase the capacity of a channel. Given
the quality of its physical medium there's a huge possibility of dropout,
loss, crosstalk etc. so the bands are monitored and any which are too poor
to use are simply not used - gets worse with distance, hence the drop off in
max. ADSL rates with distance. But it's still much higher than the rates
typically sold to customers, hence a connection can be maintained even if a
large number of the bands are useless.
Mind you, I grew up with analog telephone lines and the problems thereof and
it's like black magic to me that these kind of signal rates can be sent down
copper pairs anyway but then Mr. Clarke's words about advanced technologies
come to mind . . .
Niall
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