Switchman’s Primer on the Tone Generator

Posted: 11/11/2013 in Communications

The following information was provided by one of my readers.  “Switchman” as you will see, has extensive experience in telephony. Read and heed and add another arrow in your quiver.


I’m going to apologize up front if any of this info is too elementary. I don’t know how much experience you have around telephony, so I am just going to assume an average layman’s base of knowledge. Tracers (also called toners or tone generators) are most often used to locate specific pairs of wire over long distances. Most also have the ability to provide enough battery to allow voice comms with buttsets across a dead or “dry” pair. Here’s a link to an example tone generator made by JDSU that has the talk battery feature. http://www.electriduct.com/JDSU-TG101-Tone-Generator.html

In the phone business we deal with massive bundles of wire that are often times snarled and resemble a rat’s nest. Even in the best conditions, just trying to find one individual pair of wires out of an 1800 pair cable can be virtually impossible if the color-coded binders have aged and changed colors. There are also relatively ancient cables where the individual pairs are all white. We refer to those as “tone cables” because the only way to find your pair is to put test tone on it at one end and then find that tone on the other end with an inductive probe.

When performing maintenance you often have techs on either end of a cable. One way they can talk to each other is to find a dead pair (no battery on it), then put test tone on it at one end with the toner. The tech at the other end finds the pair with an inductive probe or sometimes even with just a buttset. Once the two techs know they are on the same pair, the toner can be placed in series with a buttset and switched to “talk battery” mode to provide the voltage needed to carry voice over the dead pair. The other end just uses a buttset, you only need one toner to provide battery.

I can’t find specs for the range of voice comms using this method, but these little toners can send test tone over 10 miles. To put a toner in series with a buttset simply connect one lead from the buttset to one lead on the toner, the two remaining leads are used to connect to the pair being used for comms. When being used in this configuration, the end with the toner can “ring” the other end by simply switching to test tone and then back to talk battery. It won’t actually ring the other buttset, but it will generate that same warbling 2 freq test tone on the other end used to locate the pair in the first place.

I hope I haven’t lost you at this point. If there is anything I can clarify about this setup or any other telephony info please let me know. I’ve been working for a “Baby Bell” for 15 years and grew up around it as well.


Thanks for the info. Switchman, feel free to contribute at any time. That goes for the rest of you folks out there in  the blogosphere that have communications technical experience that is pertinent to our mission (METT-TC).  This is not a one man show.


Dan Morgan


  1. bmw says:

    Great post, I’m up to speed here from prior experience. A little more info; the tone generator will i.d. one pair of the telco wiring that is active, in use, dead or spare from one b-box or pedestal to the next, most telco wiring schemes center around a central office, or CO, and radiate wire, or fiber, to their customers. Usually averages 2-5 mile radius from CO, more with the advent of digital circuits. Either underground or aerial telco infrastructure is commonplace in rural to major metro areas, a little surreptitous work and you could have a hard wired net or remote comms or what-not…. I like the what-not… Forewarned; This infrastrucure is maintainence intensive and easily observed or monitored by the CO. A pair here or there clipped to a well camo’d connection will go unnoticed, especially if done in the same manner as the telco. Shop at Grainger, even Ho-Depot hase similar hdw. Do not disrupt service or run up charges/damages, (unless required), and you will likely go undetected.
    The tone generator, (fox) works with a hand held inductive pick-up, (the hound), one at each end of the pair. The hound, being inductive, can be waved in proximity to the wire bundles, or “rats nest” as Switchman knows it, to find the line or pair the fox is attached to.
    Additionally, the hound, being inductive, can pick up audio over POTS, (plain ole telephone service), What he says on powering the butt sets with the fox is true too. You would have to listen close on the butt set to hear the tone of the fox if used as a comm link, and would need to clip in another fox, (1 butt + 1 fox at each end) just for signalling. The fox usually has a three-way switch, tone-off-talk, and when off, while connected to a pair, will indicate through an LED the line state or if it has battery, 48vdc, by color of the LED. Another thing, on POTS, its 48vdc for the loop batt, but 98vac for ringing. Numbers approximate, but easily found on internet. I’ll add that data lines, or digital circuits, sound like noise and hash on the hounds and if you use an analog butt set, it will trip the line and cause an automated trouble report. Lots more possibilities exist to exploit when appropriate, always include a “Switchman” in your tribe or commo plans!

  2. BLAIR WARNKE says:

    Two other items to remember; the hound being an inductictive pick-up, usually with a speaker as well as terminals to hook up a butt set can be used to listen to conversations without contacting any wiring. 2-20 cm distance will pick-up audio on lines and not just telco. For all newer digital lines and phone systems, data safe butt sets can be had that won’t trip connections.

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