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Tone and Probe is a procedure used for tracking down a specific wire out of a bundle of wires, or finding which device goes to a certain port or plug. A useful practice when working with phones, networks, or almost anything involving long wires.

Lets say your working onsite on a 10BaseT network and a computer has a bad network connection. So test the cable, you might be thinking. But sadly, whoever ran the connection didn't label anything. If theres one hundred other computer's network connections coming into the same wiring closet and you have to track down one to test it, and nothing's labled, your best option is to tone and probe.

A basic tone and probe kit consists of an inductive amplifier and a tone generator. The amp is a wand shaped device which picks up any electrical noise near it, like fluorescent light ballasts, AC power lines, LED displays, even stuff in computers. It plays this noise aloud through a small speaker or butt set.

The generator is a small box that you connect to the wires to be probed via alligator clips. It sends audio tones down the wire, which can be heard anywhere along it's length by the amp. The tones are typically just a "high-low-high-low-high-low" sequence, easily discernable from other electrical noise. The generator can usually do other nifty things, like test continuity, the status and polarity of a POTS line, or even serve as a battery for butt sets.

So back to our onsite job, you just plug the generator into the wall jack of the troubled network connection. Then listen to the toner with the amp before you leave. If you don't hear it now, something is off, or you have a dead battery! Then, in the wiring closet, use the probe to find the trunk of cable with a wire in it that says "high-low-high-low". Then just trace along that truck to it's patch panel, and you then you can tone the wire down to it's exact port. Now that you know where it is, you can unplug it use your cable tester to run further tests.
If you never hear anything, you need to check in another closet, or the wire is broken somewhere, or the jack by the user is shot.

That's a mile high view of it... there is certain ear and zen that has to be developed. Some makers of tone and probe kits of all sizes are Harris and Progressive Electronics.

Technical note:
There can be ill effects to plugging a generator into wires that leads to live equipment (a switch, phone system, etc). I've never had any network equipment come to harm from toning, but I have had phone systems power down a card I was plugged into before (opps). Of course, you can't unplug everything from whatever your testing in the middle of the day either. The trick is to test on dead wire in the cable, for instance to tone a network connection, I usually tie wires 7+8 to positive and 4+5 to negative on the generator (I carry a female RJ-45 plug with a pigtail on it for this very purpose). These wires arn't used in a normal connection. Of course, they very well might still lead into the circuitry of your switch. Be careful.

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