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Ask HN: Cablefinder to find telephone cables in the wall

2 points by fefferkorn ↗ HN
I have the need to find a certain cable in a pack of cables (harness) (i would say about 200). they have not been marked. so i only know the start and the end, but i need to find where it goes in the walls. Is there a device where i can bring on a modulated signal (to eliminate noise from other data cables) and track it through thick walls? but also directly? i know some (expensive) FLUKE devices, but they only allow to trakc half a meter i think. Im not an expert when it comes to electricity and antennas. Is it possible to build such a device myself with a raspberry maybe? Has someone done this? Thanks for advice!

9 comments

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theGeatZhopa
As I understand you have a bunch of cables and you know the start and end... Then .. you know where it's going to :)

This trackers for electricity in the walls track magnetic fields caused by the current in cables. They mostly differ between Metal/electric/nothing and have three signals. If it possible to disconnect all of the cables in the bunch of current and just connect to supply current on the one cable in question, then it would be possible to track it. Other cables would be recognized as metal and showing a different signal.. may be like this?

fefferkorn
thaaats true ;), but the problem is, i want to add another cable but im stuck in between and dont know where, and i dont know why, its a few hundred meters of cable, they go into different holes and walls, split and come together..i can not turn off all of them, different flats or offices. I know the electric tracers, but i need to trace a special one without disturbing the others too much. There are also lots of different cables (old telephone with data, fiber, cat with data, power with current, all together). Thats why i had the idea with a modulated signal. Any other thoughts?
theGeatZhopa
If you can't disconnect all of them, then disconnect the one you want to find and look in the end which one isn't carrying current. So you somehow need access to start and end of the cables. Or you need a professional equipment with (inductive) tone generator.

Or, if you have access to the end of the cable in question, you can try to connect it to a pulsed current source (on off on off) and at the start simply check with a tester which one has on off on off..

Similar possibly is it to switch on off load in the end (like having pair of 2k W hair dryers) .. then in the start it's possible to measure the amperes with a Amperemeter or something with volt that should also change a little bit rhythmically?

Indirectly measuring the energy consumption (inductively) :)

Modulation of a signal on top a current, nahhh I don't know. To dangerous. Ask a professional, may be? Make your work be magically someone else' problem hahaha

fefferkorn
its actually another cable pair where some are connected and some are not. so i can use one wire for that. Its a telephone cable, so i wont be able to push high amps or current through, but yes, i can connect aome generator on our end and use an antenna, i know where the end terminates but incan not access it (its behind a wall plate with a key). someone already gave the hint with a fluke intellitone, which has the abillity to use the sensor as antenna, but i dont know the detection range (i probably need a.few.meters, but it has not to be milimeter accurate)

i can not open the cable in between, its not ours, i just want to use it on howto find out where and how it is layed

tssva
Search for “wire toner”.
fefferkorn
yeah we already had an electrician / telecom technician here with such a device, but they only were working close range (1-3 centimeters) and had too much noise after a few centimeters of distance to the cable. But yeah, thats a good searchterm, i just came up with cable tracer or cable finder. Tone generator is also good.
fefferkorn
the intellitone pro 200 looks promising, any experience with it?
tssva
Unfortunate not. My experience using wire toners was mostly in the mid-90s when I was doing cable plant installations.