'How Do I Stop my Phones From
Interrupting My Modem'
7-21-94 by John Lundgren Ver. 950715a
Telephone mini-FAQ: Please Read
_before_ you ask in a Usenet Post
First off, have you taken the time to look at the messages in the
newsgroup, especially the newsgroup that is appropriate for the
question you have? This question comes up often, but not in the
appropriate newsgroups, which are comp.dcom.telecom.tech, comp.dcom.telecom, alt.dcom.telecom, comp.dcom.cabling.
Synopsis:
Q1. How do I stop the phones in my house from interrupting my
modem session? Or how do I make a 'Phone In Use' indicator?
Q2. What voltages and signals are on the telephone line?
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Q1. How do I stop the phones in my house from interrupting my
modem session? Or how do I make a 'Phone In Use' indicator?
A1. There are at least three answers to the 'Phone In Use'
indicator question. One is to go to your favorite Radio Shack
store and buy the Cat. No. 43-107 Teleprotector. It's about $10
(US) as of mid'94. It is put on _each_ of the phones that you
don't want interrupting your modem session. This is _not_ the
best or cheapest solution.
A2. A second answer is to connect a blinking LED light to the line
at each phone, so that it warns the user not to pick up the phone,
but it doesn't stop them from doing so. But the problem here is
that it requires power, and connecting it to the AC has possible
hazards and legal problems, as in violating FCC part 68 rules.
And if you use batteries, then they have to be changed every so many
months. Radio Snack has the cat no. 43-108 Line In-use Indicator
for about $10.00.
A3 ==THE REAL ANSWER==
Another very effective answer is to connect all the offending
phones to a line that plugs into the back of the modem, so that the
modem can disconnect them during a session. This requires no power
or batteries, and is perfectly legal, and simple.
There are a few assumptions that we have to make.
1. This is the only phone line that is used in the house, or that
all phone jacks have an extra pair of wires available.
2. The phone line is a standard 'POTS' (Plain Old Telephone
Service) line. NOT a party line, or PBX line.
3. The modem is the kind that disconnects the phone when it's
online. Some of the cheaper modems didn't do this. If not,
you could do it manually with a switch.
There are a few objectives that we would like to meet here.
1. Keep the existing jacks as they are, so that we can go back to
the original system if things don't work out. And if someone
unplugs the modem or the new jacks are not working, we can
plug the phone into the original jack.
2. Make a system that really will prevent the other phones from
interrupting the modem.
3. Do this with a reasonable amount of time and money. And keep
it simple and easily understood by the layman that has some
experience with electrical wiring. And have a safe system.
If you're somewhat proficient with a screwdriver, you can do this
with some telephone wire and some modular jacks. It's relatively
easy if you have the correct wire installed.
First thing to do is determine that all the phone lines in the
dwelling have two pairs, or four wires, and that the second pair is
not being used. If so, then you can proceed to the next step. If
not, then you may need to do some rewiring. If rewiring scares
you, you can do it with the silver satin wire that you can buy in
hundred foot rolls( about $11). You can buy the crimp-on modular
connectors and the crimp tool ($10 US). The wire is just laid on
the floor and can be taped down.
The idea is to create a second line that goes to all phones
including the modem. This second line, which is the second pair,
is connected to a second modular jack at all the phone locations.
But it is NOT connected to the incoming phone line.
The black and yellow wires of the second pair are connected to the
second jack. The black wire is connected to the G screw terminal,
and the yellow wire is connected to the R screw terminal.
It doesn't matter where the modem is connected to the second pair
of wires, just as long as all the second jacks are connected to the
black and yellow wires, and all the black and yellow wires are
connected together.
From >--'Tip' Green----+---------------------------- To existing
|
|
Outside >-- 'Ring' Red----(-----+---------------------- Phone Jacks
| |
| | ================...
| | I
+-----(----------I
| I 'Line in' jack
+----------I
I MODEM
+------------I
| I 'Phone' jack
| +------I
| | I
| | =================...
| |
Second Jack | | Second Jack
<-- 'Tip' Black-or wht/org---+-----(----+---------> To other
to other phones | | Phones
in the house | | In the
<-- 'Ring' Yellow-or org/wht-------+----(-----+---> House
| |
| |
+-----(--->
| Etc.
|
+--->
You'll also need another modular cord, long enough to go from the
modem to the jack.
If you're using the stick-on surface mount jack, mount the jack to
the wall, where it's easy to reach. Label the old jack 'Line In'
and the new jack 'To Phones'. If you have a jack cover plate on a
hole in the wall, then you can replace it with a dual jack cover
plate.
Strip off the insulation from the wires a half inch or so. If you
use a knife or anything sharp, make sure you don't knick the wire,
which can cause it to break.
On the 'To Phones' jack, connect the SECOND pair 'tip' (black or
white/orange) wire to the G screw terminal. Connect the 'ring'
(yellow or orange/white) wire to the R terminal. If the existing
black and yellow wires inside the jack are too short, you can
extend them with the telephone butt splices which crimp on with a
pair of pliers.
If there are two cables at the jack, one from the entrance and also
one going to another jack, then you have to connect both black wires
to the G terminal and both yellow wires to the R terminal of the
second jack.
Make everything look decent with some staples, and put the covers
back on the jacks.
Connect the 7 foot modular cord from the 'Line In' wall jack to the
'To Phones' jack on the modem.
At the point where the phone line enters the dwelling, you have to
connect the second pair. All the black wires have to be connected
together, and all the yellow wires. Any second line from the CO,
in other words, the black and yellow wires from the CO, must be
disconnected
At the modem location, connect the modular cable from the original
jack to the second jack. Go around and disconnect the phones from
the original jack and to the second jack.
Essentially, you are making a second line through the whole house.
If you've followed the procedure so far and the modular jumper
cable is plugged into both jacks, then you should have your phone
service back. If you unplug the modular jumper, all the phones
should go dead. If some work but other do not, then you will have
to trace the wires back and check to make sure all the black and
yellow wires are connected at all places.
Now plug your modem's 'Line in' jack to the original jack, and the
'Phones' jack to the second jack. All the phones should work until
the modem goes online, then they'll be disconnected. All the newer
phones have circuitry that is not polarity sensitive, and you can
connect them either way. If you have the older standard touch-tone
phone and it gets dial tone but won't dial, in other words, the
buttons don't make tones, then the wires may be switched. Just
switch the green and red wires at the jack.
===============================================================
Q2. What voltages and signals are on the telephone lines?
A2: As long as the phones are on-hook, i.e. there is no phone using
the line, the voltage across the line is around 48 to 54 volts DC,
supplied by the C.O. batteries. Normally, the 'tip' or green or
white/blue wire is negative.
When someone calls your number, the CO (central office) puts
ringing current on the line. This is around 90 volts AC at 20
Hertz. When the phone is picked up, it draws DC current, so the
voltage drops quite a bit. The CO senses that the phone has gone
off-hook, i.e. has been picked up, and stops ringing, and connects
you with the other end. During this time when the phone is off hook,
the voltage is somewhere between 6 to 15 volts DC, but that can vary,
depending on how many phones are off hook. The current is somewhere
between 20 to 40 mA, but this depends on how long the line is from
the CO to your phone. Since the current varies, the voltage varies
also.
The voice signals ride on top of the current from the CO. The
signals from the far end are weaker than your voice, so there is a
circuit that splits the two signals and sends the far end to the
earphone, and sends yours from the mouthpiece to the other end.
When you hang up, the CO senses that no current is drawn and
disconnects the connection.