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Gp Coil Question


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Hey guys. I've had a gp extreme for years, but never used it much, as I'm mainly a relic guy. But landed a permission last year, and stumbled on a real nice patch. This is Northern Cali...soil is rocky clay, not too bad, I run a Deus and Monster without too much trouble, except areas of hot rock. Anyway, been using the stock 11 inch coil, and getting nuggets to 2 dmt,down to around 12 inches. I'm ready to buy a 17x13 Evo coil,to see whats deeper..but here's my question...it's on a hilltop by a river canyon. Side I'm working, is uninhabitable. Directly across river, is subdivision, houses less than a mile, as the crow flies. I'm worried about EMI. I know if you flip that switch on the Extreme, it turns off half the windings in the DD coil. If I do so, would that be a good test, to see if a Mono coil will work here? I don't want to spend $500 on something, that won't be able to use here. Btw, I did pickup someone's cell phone or ham radio once before, lol.

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I found that if you switch a GP series DD coil to mono you will lose depth on deep nuggets but will get a boosted signal on a swallow nuggets that are very small for the DD coil. You would be better off burying a few nuggets of your area size at different depth and see what effect it has when you try both modes (DD or Mono) that should give you the best outcome and you should see the EMI effects also.

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Thanks Geof. Guess my question really is: is switching it to mono, really the same thing as using a mono coil? I plan on testing it Sunday, to see if it picks up too much EMI. 

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2 hours ago, deathray said:

I know if you flip that switch on the Extreme, it turns off half the windings in the DD coil. If I do so, would that be a good test, to see if a Mono coil will work here? I don't want to spend $500 on something, that won't be able to use here. Btw, I did pickup someone's cell phone or ham radio once before, lol.

It will work as a test to see how a mono (in general) works there, but it won't necessarily indicate how well a bigger coil like the 17x13 will work in the same place.

If you are running an 11" DD then flipping the switch will basically now have you running a 6x11 mono, which is a pretty small coil. The larger the coil, the more susceptible to EMI it will be. A 17x13 Evo is a big coil when it comes to EMI.

That said, I've run the 17x13 without issues with subdivisions in sight in Arizona and done ok. But then in other places further out it was getting so much interference I had to switch to a smaller mono. It kinda just depends on the location. Being too close to powerlines is always a problem though.

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16 minutes ago, jasong said:

It will work as a test to see how a mono (in general) works there, but it won't necessarily indicate how well a bigger coil like the 17x13 will work in the same place.

If you are running an 11" DD then flipping the switch will basically now have you running a 6x11 mono, which is a pretty small coil. The larger the coil, the more susceptible to EMI it will be. A 17x13 Evo is a big coil when it comes to EMI.

That said, I've run the 17x13 without issues with subdivisions in sight in Arizona and done ok. But then in other places further out it was getting so much interference I had to switch to a smaller mono. It kinda just depends on the location. Being too close to powerlines is always a problem though.

Thanks brother. Guess there may only be one way to find out, haha.

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 A GP with a stock DD coil is very hard to beat. Just go real slow with lots of overlap. I'm not disappointed with my Evo coil but my money might have been spent better elsewhere.

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The nice thing with Minelab and related coils is they hold their value and are easy to resell.

So even if you find emi levels intolerable, the "rental fee" wont be much and you can just re post the coil on the classifieds  here.

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You should ask around if someone has one second hand they'd sell you? With so many people jumping ship off their GPX to the 7000 or 6000 there is probably a bunch of larger Mono's floating around not being used anymore.  Buying brand new with so many being neglected might not be the best approach.

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On 7/21/2022 at 9:26 PM, deathray said:

.... I know if you flip that switch on the Extreme, it turns off half the windings in the DD coil. If I do so, would that be a good test, to see if a Mono coil will work here? I don't want to spend $500 on something, that won't be able to use here. Btw, I did pickup someone's cell phone or ham radio once before, lol.

A DD in the "E" (mono) switch position will run a little quieter than a straight mono coil, but it should still give you a fair idea. I.e. If in "Normal" (DD) the coil is very stable, but when you switch to mono mode you are getting a lot of false signals, then you can be pretty sure a straight mono isn't going to work out. 

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