Mark...I would NOT use coax. Most telephone cables of recent vintage should have at least two pairs in there and one is usually unused unless you've got a second phone line. So what I would do is check the existing wiring and use the unused pairs and then tap that off with a junction box somewhere. Otherwise either tie a telco cable to the coax and pull it through the wall or just drill a hole and run a cable.

That's my $0.02. ;-)

leon

* Mark Henigan wrote, On 2/10/2008 10:29 PM:

Mark Henigan wrote:

A very off-topic question aimed at anyone on the
list with telco experience.

I have a second phone line to install that only
needs to run to one room. There is already an
unused coaxial cable from a previous installation
by a cable TV company connecting the area of the
junction box to that room. The incoming phone
line is only a two-wire connection. Would the
impedance/capacitance/inductive load of the coax
be compatible with a telephone connection? I'm
trying to save the trouble of installing
additional premises wiring in a house that we
rent. Making adapters to allow modular
connectors to interface with the coax is no
problem for me so long as the characteristics
of the line would allow it.

TIA,

- Mark

Mark Henigan

Ed Durrant replied:

Phone lines are usaually 600 Ohm impedance, co-ax on the other hand is 50 or 75 Ohm.

I'd try it since it's there - the worst that I would expect is that the volume on one or both phone units will be lowered and if that's the case you can easily disconnect the cable. Chances are it'll work fine.

Hello Ed:

I think I need to describe the situation a little
more clearly, given your reply and several others.

I am talking about a second telephone line, not
splitting a single phone line.  The new line is
for my business number.  It runs to my home
because I am only in the office with a door that
bears my name one day a week.  So, I chose to have
the address listed as the office location but the
installed line at my home where I could have more
efficient access to it.  My wife is my assistant
and will be able to use the line for reception of
messages and to schedule appointments.

The telephone company (AT&T) originally installed
it without installing a connector kit on the
connection box inside a small metal access door
on the side of the house.  I called and was able
to get them to send a repair person to install the
connector kit (it includes a screw-down terminal
strip and a modular jack) so that I can install
the premises wiring.

There is a run of coax from the access box to the
room that I intend to use as an office.  It was
installed on the outside of the house and is no
longer than 15 feet.  There is no telephone line
to that room.  The other telephone jacks in the
house are connected to our home number.  This
means that there is no run of cable or telephone
wire to use to pull through new wire.  There is
also no point for access to the new line where it
can be easily connected to the electrical power
wiring of the house.  Note that the other side of
the wall where the access box is located is the
garage and would allow a surface run of telephone
wiring to a point where I could drill vertically
to enter the wall of the office room.  However,
the coax is already installed and enters the room
next to the desk.  It will only carry standard
telephony and possibly fax (not a show-stopper if
it is impractical).

Standard analog telephony uses approximately 40V
connections, although Will makes the point that
the ring tone is at 135V.  The use of UTP for the
majority of connections leverages both its
ability to cancel inductive interference and its
differential signal.  However, a short run of
coax can avoid induction and can carry signal
through both shielding and center wire.  In some
audio frequency applications the shielding of
coaxial cable (admittedly with different
construction and characteristics such as
microphone cable) is intended to carry current;
although this causes ground loops in many
configurations requiring isolation transformers).
I realize the foil shielding of much HF coax is
not a great conductor.  However, it should be
adequate from what others (Ed and Jeffrey) have
said.  If, as noted by Jeffrey the cable or
connectors are of poor quality or condition, I
can always install a new connector (I have a
compression type installation tool.) or remove
the cable and install telephone cable in its
place.  I'd rather avoid the latter since the
cable enters the house of the second floor.

So, thank you all for your suggestions and
thoughts on this rather confounded question!
I'll try the installation using the coax and
revert to replacing (or adding a run of phone
cable in parallel with) the coax if it does
not work.

Again many thanks!  There is so much knowledge
available on this list!

- Mark

Mark Henigan
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