[Gllug] Multiple ADSL splitters

[Chris Bell]

On Tue 14 Nov, Matthew King wrote:
> I am rewiring the telephones in my house and need advice from real
> people rather than websites.

   To be absolutely clear about the wiring, the original telephone wiring
before ADSL would have looked like this:

          /\   Incoming twisted pair
          \/
          /\
   ______/  \______
  |                |
  |------>  <------| Anti-surge spark gap
  |          ___   |
  |--||--.--|___|--| Ringer circuit with capacitor and resistor
  |      |         |
  |      |         |___  Original pair plus
  |      |_____________  ringer wire connected
  |____________________  to phone and all extensions
       
   The extensions are normally wired using a twisted pair plus a single wire
from another pair. The ringer circuit is not likely to pick up any signals
that would interfere with the telephones, but the ADSL system is much more
likely to see increased noise. There can also be significant carrier loss in
the local wiring and any phones connected, and it causes noise on the phones.
   The ADSL carrier on the incoming pair is connected direct to the modem,
and should be totally blocked from the remainder of the telephone system.
   The ADSL modem input has a high pass filter which blocks normal telephone
frequencies.
   The full specification ADSL filter blocks the carrier from the incoming
line pair to the telephones with a sharp cut-off balanced low-pass filter,
acting equally on the two wires, breaks the existing ringer wire, and
supplies a replacement ringer circuit after the filter. This makes it much
easier to design an efficient filter, although the replacement capacitor and
a high quality filter capable of handling the full telephone load are
relatively large.

-- 
Chris Bell

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