Dave Plowman (News) wrote:

In article ,
JANA wrote:


Phones need 48 Volts DC with an in series of 600 to 800 ohm source. The
ring is 96 Volts at 25 Hz.



That's the spec to allow for vast voltage drop over the miles of cable
between phones. Just to get two to talk to one another 9 volts will work
just ok. Indeed if you're talking about old non electronics phones with
carbon mics 1.5 volts will be ok for short runs.



I have always used the assumptions that there was 400 Ohms in the
telephone. The telephone wants
20 milli-Amps or more so that says you need 8 Volts or more (per phone)
The 48 Volts (really 52)
that the central office uses is to push at least 20 milli-Amps through
the longest line.

Bill K7NOM