Metal detectors and fiber optics.

[srd1941]

A couple of years ago my neighbor and I had fiber optics installed for our computer and telephone connections. The utility company had to run from their main line down the alley to the nearest pole then over to our houses. Prior to this installation my detectors all worked fine anywhere in either of our yards. Ever since the install they are so erratic as to be rendered unusable in the immediate area. Has any else experienced this?
Stan

 

[digitaltim]

There isnt any way for the cable itself to emit interference. Its a light traveling down a piece of glass.

The jacket housing the fiber may be armored / metal flexible conduit. Maybe this is some how causing your issue? It should be ground when installed / terminated.

 

[srd1941]

Now that you mention it that does sound right; however, when I moved here five years ago everything worked normally. That lasted for about 2 years till my neighbor moved in. He had cable TV brought in and fiber. There was a lot of work going on in the alley at that time. There is a transformer on the nearest pole but I think that was always there. Anyway it

 

[dixiedigger57]

same problem in the ga country side at my in-laws house. a high tech cable was put down the ditch on the highway, and forget it! pulses like a heartbeat. then the electric cattle fence out back. had a garrett once, and could not even turn it on. they eat up my tesoros bad too. i also went under a cross country power line on a choice site, same problem. I could not adjust it out. I dont understand it at all either. fiber is not metal.

 

[tvr]

I'm with digitaltim on this one. The fiber by itself is easy to break and is normally supported and protected with sheaths and strength strands even if not running through a conduit. Some of the strength and protective materials are conductive. The connector ends are frequently plastic, so there is sometimes no easy way to ground the sheath that may be conductive.

Another factor may be EMI from the converter / demultiplexer / router / tuner box they hook into. And if the sheath on the fiber is conductive and does not have a ground connection, the box EMI can re-radiate down the sheath or conduit.

As for hunting under the power line towers, some places aren't too bad, others are. If it is a choice site, try it another time. Sometimes interference can be from debris on a tower that affects a line and an insulator (birds nests, plastic bags that are dirty or wet, other stuff). Other times an insulator is breaking down. Debris sometimes clears itself, and when the insulators get bad, they do get replaced and then a lot of the noise goes away.
tvr

 

[dixiedigger57]

Will try the power line with a different detector, maybe see what a friend's PI will do for kicks. He has several different khz units, from 5 to an old Hayes 100. The area is too good to pass up.

 

[Jerry Ga.]

I can tell you this, certain makes and models of wide screen TV's will play havoc with a metal detector

 

[UtahRich]

Another factor may be EMI from the converter / demultiplexer / router / tuner box they hook into. And if the sheath on the fiber is conductive and does not have a ground connection, the box EMI can re-radiate down the sheath or conduit.
tvr

I suspect that TVR is right on. If you didn't have trouble before the install and you now have trouble after the install, I would suspect that the unit used to convert and demultiplex the fiberoptic signal is giving off a bunch of EMI.

Unplug it and see if the trouble goes away. Also, make sure that you have a good ground on the power outlet that your fiber equipment is plugged into. You can go as far as turning all the power off in the house and see if that helps. If it does, turn on the breakers one at a time until the problem returns. If it returns after switching on a certain breaker, whatever equipment you have on that breaker is your culprit.

It might not be you. Could be a neighbor.

If it is any consolation, I can hardly hunt in my yard at all. Years ago, when we first moved in, I planted a test garden, after cleaning out all the signals in all metal mode, (There weren't many) I planted some pennies, nickels, dimes and quarters at various reasonable depths (4"-8") along an imaginary line extending from a particular place on my house. I Haven't been able to detect ANY of them in discriminate mode with a half dozen high end detectors of various brands and frequencies. I can't bench test in the house or yard very well either, get all sorts of pulsating interference. I have a power pole/telephone pole in my back yard, but not a transformer. I have noticed the problem in my house is worse since we started changing out the regular incandenscent lightbulbs for the new style fluorescent bulbs. And since we moved in, wireless internet rounters and all sort of other stuff have come into vogue as well.

Good luck.

Rich