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emi problem?
Posted by: emubob
Date: July 25, 2018 04:23PM
would ground balancing help to erraticate emi.the machine i used in a park this morning didn't have ground balancing feature and it went nuts.lowering sensitivity didn't help,emubob

Re: emi problem?
Posted by: GeorgeinSC
Date: July 26, 2018 02:40PM
The only way I have found to combat EMI is using a small coil. And even that does not get rid of all of the EMI



Minelab Sovereign GT With an assortment of coils
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Leche digging tool
Minelab Excalibur II
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Re: emi problem?
Posted by: still looking 52
Date: July 26, 2018 04:40PM
My F5 has frequency modes that I can tottle around with to help EMI and it will make a difference. Check your owner's manual for information about that on your machine.
Ground balance doesn't seem to effect EMI at all.

Re: emi problem?
Posted by: MI-AuAg
Date: July 26, 2018 06:40PM
Hello emubob,

A ground balance adjustment (if you had one) wouldn't mitigate heavy EMI. Ground balancing deals with mineralization within the ground matrix you are detecting in, EMI eminates from a variety of electrical sources near the area.

Reducing sensitivity as you tried, is usually the first attempted remedy. The other possible remedies mentioned above of using a smaller coil, or trying a frequency shift (if your detector is so equipped) may be of some help.

Going to All Metal mode could help, but, if it's a trashy park, you'd just be trading one misery for another. In Disc. mode you could try reducing the level of discrimination.

Determining the source of the EMI would be a big help! Something as easy as turning off your cellphone could do it. If you are near powerlines, standing directly under them is better that at a 30-40 degree angle away from them.
Those are mostly suggestions by Dave Johnson, a design engineer at First Texas. They are contained in an article he wrote, with much more about EMI. It would make a good read for you. It's on the Fisher website.

All that said, it could still possibly be a bad ground mineralization issue. In a park near me, there was fill put there that contained a whole bunch of small coke/flyash from a foundry. That stuff in large quantity will light up a detector too.

Re: emi problem?
Posted by: chuck, ky
Date: July 26, 2018 08:01PM
Reducing the level of discrimination would only increase the noise level. As you increase the disc. some of the interference may be eliminated but it would seem like that decreasing would increase what you're picking up no only in the ground but also in the air.

Re: emi problem?
Posted by: MI-AuAg
Date: July 26, 2018 08:31PM
Quote
chuck, ky
Reducing the level of discrimination would only increase the noise level. As you increase the disc. some of the interference may be eliminated but it would seem like that decreasing would increase what you're picking up no only in the ground but also in the air.

Quote from Chief Design Engineer at First Texas, Dave Johnson's article on "Electrical Interference":

"In the Discrimination Mode, setting the discrimination level into the foil region will usually reduce electrical interference problems. However, there are many different discriminator designs out there in beeperland, and this trick doesn't work for all of them.

Perhaps I should not have said "try reducing the level of discrimination" and said, set it in the foil region, I shouldn't have presumed to know at what level of discrimination the OP would have started in. It's something I have never personally tried or had to do. Normally I can get bad EMI to a tolerable level. I was just relaying some possible remedies outlined in his article. As I said, the article is a good read, I'd recommend it to anyone who has an interest.

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Re: emi problem?
Posted by: mrwilburino
Date: July 27, 2018 01:02PM
What detector were you using, emubob?
Has it worked OK at other sites?
Have you tried a different machine at the site where you were having the emi problem?



Fisher Teknetics XP Minelab

Re: emi problem?
Posted by: emubob
Date: July 29, 2018 09:32PM
this morning i tried the ctx3030 with the noise canceling feature.reduced the noise a bit but not enough to make detecting comfortable.other day i tried tesoro's deleon,that was a total waste of time,seven inch concentric coil.the only detector that i have that worked in this park with a six inch dd coil was the xterra 705.so it looks like that ones the best all round and all the coils leads are falling to pieces.emubob

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