[Gllug] ADSL on BT phone wires

[Chris Bell]

On Wed 16 Aug, Andy Farnsworth wrote:
> 
 
> DSL modem has it's own ground, one wire is all that was necessary for 
> the DSL rather than two.  Anyone know if this is just some tech making 
> it up as he went along or what?
> 
> Andy

   Telephone pair cable uses a pair of wires twisted around each other, and
the signal is sent down both legs, with one phase reversed.
   On average the same interference is picked up on both legs and will self
cancel at the end of the cable. Using earth for the return connection will
not cancel the noise, the actual resistance could be anything, and the
effective path length will be different.
   The phone will almost certainly stop, but the higher ADSL frequencies may
just about bridge the gap thanks to a small amount of stray capacitance. It
will not be perfect, but it might work if you are only transferring small
amounts of data.

-- 
Chris Bell

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