On Thu, 31 Mar 2005 21:47:59 +0100, Andy Burns
wrote:

martin.shaw11 wrote:

How can two phones with two seperate numbers be supplied by just two wires ?
Are there some filters somewhere ?

DACS
ISDN/2 or HomeHighway
PSTN with ADSL with VoIP
in ye olden days party line, was that 2 wires plus local earth or 3
wires back to exchange?

The party line (later known as "shared service") was two wires and a
local earth. Instead of ringing current being applied across the two
wires it was sent over one or the other wire with an earth return.
Outgoing calls were originated by the calling party pressing a "call
exchange" button to send the local earth to one wire or the other.

In a very few instances where it was impractical to get a local earth
at the sub's premises a "semi-local" earth was achieved at the local
distribution point (DP) (usually a "telegraph pole!") which always had
an earth connexion.

If you were really clever you could rehash the setup to make your
outgoing calls as if they were from your very old next-door neighbour
you shared the line with, who would never dream of querying her
bills... Or so Im told.

--
Frank Erskine