I have what I think is an unsual question which I couldn't find an
answer to: in my attic there is a coax splitter with several coax
outputs to coax cables which snake into the ceiling and disappear in
the boweles of the house. They are all of the same color and have no
identifying marks. In the house itself, there are coax jacks in
And now the question: is there a way to determine, without buying
expensive equipment, which cable in the attic leads to which room?
Since not all coax jacks in the rooms are connected to a tv, it's not
just a matter of disconnecting one cable after another from the
splitter and seeing which tv loses its signal.
"Since not all coax jacks in the rooms are connected to a tv,
it's not just a matter of disconnecting one cable after another
from the splitter and seeing which tv loses its signal"
I can think of two ways right away. The way I would do it is
to get a small TV and conenct it to a cable outlet. Turn the sound
up high. Go in the attic and perhaps with a helper listening
disconnect one coax at a time. bingo.
the hard way would be to use a volt-ohm meter. disconnect all the coax
in the attic and jumper one outlet
across itself. then check in the attic for the line with 0 resistance.
Cut a small cable in two.. On one cut end wire up a 9v battery connector. On
the other cut end wire up a buzzer, or at least strip it so you can use a
meter to test the wire and shield.
Hook the 9v at the wall outlet. Go up to the splitter and check each lead
that comes up to the splitter. When you buzz, or get a 9v reading, you've
found that room.
: > And now the question: is there a way to determine, without
: > expensive equipment, which cable in the attic leads to which
: > Since not all coax jacks in the rooms are connected to a tv,
: > just a matter of disconnecting one cable after another from
: > splitter and seeing which tv loses its signal.
: Cut a small cable in two.. On one cut end wire up a 9v battery
: the other cut end wire up a buzzer, or at least strip it so you
can use a
: meter to test the wire and shield.
: Hook the 9v at the wall outlet. Go up to the splitter and check
: that comes up to the splitter. When you buzz, or get a 9v
: found that room.
Good grieg, Charlie Brown! That's the hard way, and destructive,
too. Read the previous post - much easier and cleaner and more
dependaghle and a lot less destructvie.
Sorry for the newbie question, but what happens if there is a splitter?
Also, is possible to tell - and if so, how - if there are one or more
splitters between the attic and the room?
And, another also, will the presense of one or more splitters affect
the other approach suggested by others on this thread (volt-ohm/multi
At least thehick's other idea - using a portable tv - should still
If there's another splitter, then it depends on the particular splitter
in question -- some will pass DC, others won't. If it doesn't pass DC,
then neither the buzzer nor the meter will register the battery's
As for using a TV, it'll introduce some ambiguity there, too, since you
might have two (or more) equally good signals.
If you have the same number of wires in the attic as wall connections,
there's probably not another splitter.
The e-mail address in our reply-to line is reversed in an attempt to
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If there were more splitters, it would be unlikely that they would be
hidden away somewhere. Splitters and connectors do occasionally fail and
they would have to be accessible for service. Depends on the
intelligence of the installer.
If the cable was daisy chained as was the custom years ago, there could
be a splitter at every outlet. My last house had a run with 9 splitters
in it. Needless to say, it didn't do very well with a broadband
also: cable tv company here will upgrade your splitters and replace the
cable ends from the pole to your jacks to deliver a nice picture to
your cable tv's.
and: maybe time to break down and buy a digital multimeter for $25.
look what you can fix with it at:
Let's assume there are no other splitters involved.
Forget the battery method.
Go to RadioShack or equivalent and buy a 75 ohm terminator.
If you don't own a test meter, get the cheapest one you can find that
Disconnect all the sets that are attached to the cable system
Put the terminator on one wall outlet.
At the splitter disconnect, all the cables.
Take the meter and at the splitter end find the cable that measures about 75
ohms between the center pin of the cable connector and the outside of the
Tag both ends of that cable.
Move the terminator to the next wall outlet and repeat.
Having an assistant who can move the terminator around and communicate to
the attic is a great time and effort saver.
Well, that's a departure from the other proposals :) Just to be on the
safe side, I'm going to get tomorrow both a buzzer and a 75 ohm
I already have a 9v battery and even a multimeter - analog,
unfortunately, but it does measure resistance, so I should be all set
(assuming by wife agrees to act as the assistant...)
As an aside, I must say it NEVER occured to me how useful a multimeter
is. Talk about learning something new every day.
On 21 Jan 2006 15:38:48 -0800, email@example.com wrote:
Unless there is a complet floor in the attic, I would follow the wires
into the ceiling, lifting the insulation a bit until I find where they
go down into a wall, from the top. In the attic, a wall looks like
the broad side of a 2x4. The wire is not likely to stray too much
once it heads into the wall. The ones you can't trace this way, you
can trace with the other methods given.
Remove NOPSAM to email me. Please let
me know if you have posted also.
Other posters have given you reasonable suggestions for identifying the
cables. But I'm wondering why it matters as long as each outlet is feeding
the same signal from the same source -- the splitter.
A caveat --
In a setup such as yours, each unused outlet should have a 75 ohm
terminator. Radio Shack has them. Unterminated cables can mess up the
signal to the active devices on the network.
"> A caveat --> In a setup such as yours, each unused outlet should have a 75 ohm
That goes for any unused connections on the spliter(s) as well. "
Wow, for someone who is regulary considered by his friends as a more or
less maven, I now feel unbelievably ignorant ): I guess ignorance is
relative... I have never heard of 75 ohm terminators, nor of the
problems caused by unterminated cables and unused connections on
splitters. As I mentioned in another response - learn something new
The center conductor of the coax is acts a small broadcast antenna (as
well as a receiver) the outer shield serves to contain the signal on the
center conductor to prevent both radiated signal leakage and reception
of over-the-air signals. The exposed end of the cable or splitter
connection is breaks the "seal" on the system and allows for leakage and
reception of unwanted signals. The terminator acts like a lid on jar and
maintains the cables impedance.
Wrong reason. The unterminated piece of cable, either open or shorted,
creates a phenomenon called a standing wave. Depending on the length of the
offending cable and whether it is opened or shorted, the wave can raise the
dickens with the right signals. Terminating the cable in the correct
impedance doesn't let the standing wave be created.
Take a look at
It talks about standing waves in a string, but the concept is similar for
liquids and radio waves.
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