Coaxial Line Tester - Point to Point ID




I recently started digging through a nest of cables in my basement only to discover that nothing was labeled, nothing made sense, and probably 50% of the cables weren't even hooked up. It appeared to me the previous owner had some kind of multi-purpose system installed for video, audio, data, etc. Naturally, it was rendered inoperable when they removed the brains of the whole system and left just an empty enclosure.

Removing the obviously not connected cables was the easy part. When it came to identifying where each connection was actually made in the house, I realized I'd need tools. A standard coaxial line tester, otherwise known as a "network line tracker" or other similar term, can be purchased from Amazon for around $22-$30 US. Usually that'd be the end of it, just wait for delivery. But, I don't plan on using this thing regularly, so I have a hard time justifying the expense when that same money can be used for other things. I did find one for under $15, it didn't appeal to me.

Step 1: Background

Coaxial cables are simple: single center conductor insulated from a braided jacket for the signal reference. There are a few types of coaxial cable, each with different gauge size for the center conductor, for different applications, etc. You can spend hours online learning about all of that.

The center conductor is the key part. The size of that conductor will determine the voltage drop in the line. For me, it was 0.04V/ft drop. That means at 100 feet, the input voltage would drop 4V. I didn't expect to find runs in my house which were longer than 100ft so I planned for that. Using Ohm's Law I was expecting a very low current draw at 100ft of line, and initially had concern it wouldn't be enough to light up the LED. But, it worked fine, so no worries. Just keep in mind the resistance will change (increase) with longer runs, and it will make your LED dimmer. Too long, and it might make the LED too dim to see.

By the way, this is my first official Instructable. I've entered into the Home Hacks contest, and the first time author contest. Please vote for me if you feel compelled to do so! Thanks!

Step 2: Gather Materials

One big reason I didn't care to buy something was that I had a bunch of scrap materials laying around with nothing to do. So here's what I gathered:

12VDC Power Adapter, commonly used for phone charging, power to small electronics, etc. The one I used is 12VDC, 1A output, 120-240VAC input. These can be found on Amazon for under $5.

10k Resistor, QTY 1.

Standard LED, 5mm. You pick the color, I chose red with a clear lens.

Coax Adapter, Male to Male, QTY 2. You can get these at most hardware stores, or electronics stores. A 2-pack cost me less than $2.

Electrical Tape

5 Minute Epoxy (Optional)

Solder (Optional)

Soldering Iron (Optional)

Hopes and dreams (Never leave home without them!)

Step 3: Step 3: Cut the Cord!

Leave yourself a few inches of wire when you cut off the end, you can use that part later for other projects. You'll need to also strip the black wire jacket off, I took about an inch off. Then, strip the red and black small wires, I took off about a quarter inch of the insulation.

Step 4: Step 4: Connect the Resistor

It will be difficult to solder the wires to the coaxial adapters, but go ahead if you'd like something more permanent. I wasn't planning to use this thing for longer than a weekend, so I just did the following:

A. Trim the resistor leg a bit on one end, and use that piece to stick into the center of the coaxial adapter.

B. Solder the red wire to that piece you just stick into the adapter. So I guess the soldering iron is useful... you can try to shove the red wire directly into the center, but you probably won't get a good connection.

C. Solder (or twist) the black wire to the trimmed end of the resistor. Did you leave enough after trimming?

D. Solder, or just tape, the long end of the resistor to the outside threaded part of the coaxial adapter.

If your lengths were good, it should fit somewhat straight. It was here that I decided to use the 5-minute epoxy to secure everything, then wrap a couple layers of electrical tape to keep it all together.

Step 5: Step 5: the LED

This one is easy. Make sure the NEGATIVE side of your LED (usually the short leg, flat side of the lens) is on the outside of the coaxial adapter. The POSITIVE leg of your LED goes into the center. Just wrap this with electrical tape, or add the epoxy before wrapping the tape if you really want to keep it secure.

Just an afterthought, the epoxy might prevent a good electrical connection with the negative leg. Make sure to keep the epoxy at the center if you use it. Solder really is a better way to make the connection, so use flux and maybe scuff the threads on the adapter with some steel wool? I haven't tried that yet.

Step 6: Step 6: That's It... Go Test!

You might want a spare length of regular coaxial cable in case you're testing wall mounted coax. I had a 1ft length laying around so I just used that. All together you should have 3 pieces: the wall plug with the resistor end, a small adapter with an LED sticking out, and a short length of coaxial cable.


I do not know what will happen if you plug the 12VDC source into the wall, and send 12VDC in reverse back to your splitters or modem. If you do this, and something breaks, don't say I didn't warn you. Before testing point to point with this rig, it's probably a good idea to disconnect all of your coaxial cables from the modem, splitters, etc. at the point of origin for the signals. For example, in your basement where the main line comes in and goes to your distribution splitters / modem.

The process is time consuming, but works. Just plug the power supply into the wall, and connect the other end to a coax outlet / line. Then, run around plugging your LED adapter into wayward ends of coaxial line until the LED lights up. It's probably a good idea to label that one, it's the one you're looking for. ;) Repeat as necessary.

As a note: if you plan to use this thing more than just one evening or two, go ahead and purchase something. Chances are it has all kinds of functionality my simple rig does not... detecting shorted lines, or signal integrity / quality, etc.

Happy Hunting!



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    5 Discussions


    2 years ago

    by the way some months ago, i did a different creation, I think it will be my first Instructable. see you friends


    2 years ago

    Your creation is just great and useful, i don't need the multimeter to check continuity, i can tell you, you would test any wire using your creation, and paying attention to the warnings. thanks so much. 100 points for you friend!


    2 years ago

    Nice idea, I have always used a shorting plug and a multimeter but I can see that this could be easier :)

    1 reply

    2 years ago

    Good info! Thanks!