EMI Interference

[Smudge]

I have been noticing on most of the Fisher and Teknetics user manuals they go to great lengths to warn users about EMI Interference.

I also see a lot of Fisher and Teknetics users describing issues with EMI on the different forums.

I absolutely am not trying to start a brand war here, but I am curious if these two brands are more succeptable to EMI interference than other detectors and if so, why would that be?

 

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[Sandman]

Electrical interference is a problem with all detectors with them being made more sensitive now days. It isn't just the Fisher brand. We are carrying cell phones, there are micro wave towers and all sorts of things that put out different frequencies that the detectors can pick up.

http://detectorstuff.com/2009/08/05...ay-by-first-texas-lead-engineer-dave-johnson/

 

[stevemc]

The bigger the coil and the more sensitive, as sandman said, the farther away a detector will pick up EMI/EMF. I have a large coil PI detector with a 5' x 3 1/2' coil, and it will pick up the large, cross the state power lines, the really powerful power lines 100s of feet away. I cant use it in a house of course, or anywhere near a large powerline. Just regular little 480 volt powerlines will make it wa-wa-wa. Phone lines not so bad. Electricity running in a wire will make an electrical magnetic field or interferance, which a detectors antena (coils) will pick up, if close enough. That is what they do, pick up electricly generated fields. Metal detectors fields are very small, and anything in that field will absorb the electricity and depending on how conductive the metal is, the detector will pick up the EMF from the metal and respond. But if there is a very powerful field much farther away than the regular field of the detector, the detector could pick it up.

 

[Smudge]

Ok, so it sounds like detectors in general have reached a state of technology, along with everything else, that we are starting to get some serious bleed-over in the frequencies.

That makes sense.

Thanks guys.

 

[U.K. Brian]

Don't forget that some detectors have frequency shift adjustment so have little bother even though they are very sensitive whilst others don't and the only way round it is to reduce sensitivity and lose depth.

There's also the question of how the depth of the detector is being achieved. If there's the choice of raising Pre Amp or just the general sensitivity of the detector then Pre Amp is often better in many respects except it maximises any interference. So with bad EMI use less Pre Amp and increase sensitivity if you have to using the standard sensitivity/gain control.

Some detectors do suffer less because they have better shielding of the wire to the coil and a properly shielded control box but others that are claimed to be good are just generally not very sensitive.

 

[gleaner1]

My 84 Garrett raises Cain crosstalking with my cz. Or is it vise versa? Such is EMI. Power lines raise Cain with all my machines. It's madness.

 

[niffler]

My DFX is pretty sensitive to interference. It gets a little better with a DD coil and the 15 khz frequency, although the only real solution is to reduce sensitivity. I also got (scavenged) a ferrite filter for the coil cable, but I can't really tell any difference between having it on there or not. HH Niffler

 

[Cable]

Just a thought---not a question or direct comment----ever think about the detecter that sits on your shoulders and ALL the signal that it receives---- Just a thought lol

 

[G.A.P.metal]

There are a lot of undergorund transformers,so if you can`t see above ground wires...and your detector wacks out you will know y.
Gary G.A.P.metal

 

[jmoller99]

2 detectors, running at the same frequency often cause EMI issues unless you stay at least 30 feet apart. So if you have 2 or more people using the same model near each other, you end up with issues. A lot of general purpose detectors run at 6.8 KHz (Bounty Hunters, ACE 150/250, some Fisher models, Some Whites models), so these tend to interact. Its easy to test this if your group of people all get together and check to see if their detectors interact before they start hunting.

 

[DirtyDon]

I wonder if it would work if someone made a Faraday cage to put around the control box.

 

[stevemc]

It is the coil that is the problem. And the type of detector. The more powerful the detector is to receive, the more it will pick up stray EMI - electrical magnetic interferance. Coils transmit and receive, just like a walkie talkie, VHF radio, or many types of radio gear. The more sensitive and powerful a detector is, and the larger the coil, the easier it will pick up any EMI/EMF. Certain types like Minelabs Sov and Excal and I assume the E types like the Explorer, which have many frequencies, and Pulse Inductions - PI detectors, also put out a powerful electrical pulse which both of those type will mess up into any other and also receive from any other detector, so they must stay way apart. Any charged electrical wiring will affect the above kinds, especially PI detectors. That makes an electrical magnetic field - EMF, and is picked up by the detector. Think of a detector coil as an antennea. It is receiving the electrical pulses from many sources (unfortunatly). I had a cell phone in my pocket and was using a PI detector and it rang, and the detector went wild.

 

[Cool Hand Fluke]

Any serious detecotrist needs both an older anoalog machine and a digital machine to help avoid the EMI problem. Some of the older analog machines are not nearly as susceptible to EMI as some of the newer digital units. I'm not an electrical engeener, not sure as to why this tends to be true.