30VAC at 1KHz? Sounds like a good excuse to get that old Crown DC-300A from the shed! Thanks for the tip. I figured it would be something simple. I have an old inductive "telephone handset amplifier" that I can use as the receiver, I'll substitute the pickup coil with an antenna. I probably should make a handle from a paint stirring stick to reduce body coupling. Square wave, I assume? Thanks! Bob On Wed, May 15, 2013, at 09:40 AM, Dwayne Reid wrote: > I have a bit of experience with this kind of stuff and my buddy does=20 > underground utilities location professionally (its his day job). >=20 > 1) A couple of people have suggested using divining rods. Seriously,=20 > its worth a try. My buddy Russell (the guy who does this=20 > professionally) uses divining rods whenever he has to locate old=20 > sewer pipes that he can't connect his electronic tracing gear to. He=20 > says that it works well for him. >=20 > Me: I can't offer an opinion. I haven't observed divining in=20 > operation nor have I tried doing it myself. But I absolutely won't=20 > discount its effectiveness. >=20 >=20 > 2) The easy way to do this electronically is to attach a relatively=20 > high voltage 1KHz signal to one end of the wire. Grab any old audio=20 > power amplifier that can deliver at least 20 or 30 Vac (rms), ensure=20 > that the ground end of that signal is actually grounded (near the=20 > line if possible), and connect one conductor of that line to the=20 > output of the amplifier. Then use an equivalent of a "Hound"=20 > telephone line tracer. If you have one, use it. Otherwise, just use=20 > an audio preamplifier that can handle low-level mic signals. Attach=20 > a length of unshielded wire to the preamp's input and make sure that=20 > you can hear the 1KHz tone from more than a foot away. >=20 > If you have an old PA amplifier with a 70V speaker output, use that=20 > to drive the line. >=20 >=20 > I've got an old piece of Telco CO equipment called a "Jumper Tracer"=20 > - its used for tracing long jumper wires in an old-fashioned Telco=20 > Central Office. That's where all of the incoming subscriber wires=20 > wind up on large walls of dense punch-blocks and need to be=20 > cross-connected to the switch equipment. It uses a fairly-low=20 > frequency RF carrier modulated at 800Hz or so. The pickup wand has a=20 > coil wound on a short piece of ferrite rod at its end - this coil=20 > connects to the pickup unit with a piece of shielded twisted-pair audio > cable. >=20 > This unit is absolutely marvellous - I can trace wires that are=20 > inside conduit buried under six or eight inches of concrete. But if=20 > your wires are not inside metal pipe, its really easy to detect an=20 > audio-frequency electric field using that power amp mentioned above=20 > and a Hound listen unit. >=20 >=20 > Finally, my company makes a couple of pieces of equipment used for=20 > detecting coating damage on buried pipelines. The transmitter sends=20 > audio-frequency current down the pipeline and the detector is a=20 > hand-held large-diameter walking stick that connects to the backpack=20 > that the survey guy is wearing. The pickup elements (there are 5)=20 > are circular coils that feed high gain, very low noise preamps. When=20 > all is said and done, we wind up with the depth of the pipeline (if=20 > it is buried or under water) and the magnitude of the current at that=20 > location. All of that data is logged along with the GPS=20 > coordinates. All the guy has to do is walk along the pipeline's=20 > path, swinging that thick walking stick from side to side. Every=20 > time the stick is exactly in line with the pipeline, he gets a beep=20 > from the receiver and the current measurements are made. The beeps=20 > help keep him on track when he doesn't know exactly where the line is=20 > buried or if he is in a boat. >=20 > This gear is good for taking measurements several miles away from the=20 > transmitter. But its WAY overkill for what you need to do. >=20 > dwayne >=20 >=20 > At 10:57 PM 5/14/2013, Bob Blick wrote: > >When the power company wants to follow the path of a buried cable, they > >attach a gadget to one end and walk along the ground with another > >gadget. Looks real easy when you have that $7000 pair of gadgets. > > > >Any idea what inexpensive thing I could modify to get a similar effect? > >I don't need to do it on a live wire, and the maximum depth underground > >is one meter or less. > > > >Thanks, > >Bob > > > >-- > >http://www.fastmail.fm - Send your email first class > > > >-- > >http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > >View/change your membership options at > >http://mailman.mit.edu/mailman/listinfo/piclist >=20 >=20 > --=20 > Dwayne Reid > Trinity Electronics Systems Ltd Edmonton, AB, CANADA > (780) 489-3199 voice (780) 487-6397 fax > www.trinity-electronics.com > Custom Electronics Design and Manufacturing >=20 > --=20 > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.fastmail.fm - Access all of your messages and folders wherever you are --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .