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Will A Smaller Coil Help Me And My Garrett AT Max?


mh9162013

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I got in a few hours of hunting at an interesting permission this weekend. It's the construction site for an expansion to my local library. They already cleared out much of the top 6" of dirt, trees and shrubs. So all that's left are a few inches or rocks/rubble and sand, then highly mineralized clay underneath. Oh, and trash. Lots of trash. There's so much trash, it's impossible to ground balance in that area.

So the approach I took was going into custom mode and notching out anything that was 68 (or so) and below. Basically, I was looking for coins (except nickels). I noticed that I'd often get a lot of short high tone "chirps" that I could not get to repeat, or could only repeat once or twice. I guessed that my detector was getting a "high VDI" target, but due to the trash and the size of my coil (stock 8.5x11), it was struggling to separate the "target" from the trash I had notched out. 

I also had sensitivity around 3 or 4, although boosted it to 6 or 8 to get a better read on a potential target if I thought I might have something. I did this because at least 6 inches of the top ground material had been moved into large piles or taken away by dump trucks. So I figured if there's anything good in the ground, it wouldn't be deeper than 6 inches or so. And if there's anything good that's deeper than that, I didn't want to spend the effort to dig it. I was digging in ground that was so soft and muddy due to heavy rains, I was sinking into the ground worse than wet sand.

All that being said, here's the reason for this post: It's my understanding that I would have had a much easier time sifting through this construction site for coins if I had a smaller coil. The top 2 contenders for me right now are the 5x8 Garrett and the 4 inch Garrett hockey puck. Is my understanding correct? And if so, what would you all recommend if I could only pick just one of those coils? Or would you recommend both...or a different one? Also, another reason I'm thinking about a smaller coil is to reduce the weight of my machine.

My current thinking is to get the 5x8 and use that full time, with the hockey puck on occasion. Then I sell the 8.5x11. And in the rare cases I need full depth AND there's little trash, I buy a NEL Storm or something along those lines.

I'm considering the smaller coil b/c this isn't the first time I've received a permission to hunt a promising location that's filled with a lot of trash.

Thanks ahead!

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The 5X8 is a good choice for an all around coil. The 4.5 is a specialty tool. I would keep the stock coil for less trash sites. It is a very good coil in the right conditions. I am a big believer in having multiple coils for each detector.

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13 minutes ago, JCR said:

The 5X8 is a good choice for an all around coil. The 4.5 is a specialty tool. I would keep the stock coil for less trash sites. It is a very good coil in the right conditions. I am a big believer in having multiple coils for each detector.

If you had the 5x8 on your AT Max and you could choose from b/w the stock 8.5x11 or a third party large coil, like the NEL Storm, which would you choose and why?

And if the 4.5 inch hockey puck isn't designed for trashy ground, what's it good for?

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The 4.5" coil's specialty is dense shallow trash or in/around playground/fence poles. If I were to get a larger than stock coil it would be the new Garrett Reaper. I have always found their coils to be excellent on their machines.

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47 minutes ago, JCR said:

The 4.5" coil's specialty is dense shallow trash or in/around playground/fence poles.

Sounds like that coil might be great for me. I like to hunt tot lots and areas with lots of trash and potentially shallow targets.

When I get a permission, I usually avoid digging deep. Even when there's no risk of damage to lawns or yards, I have limited time to hunt and it's usually not worth the added effort and time to dig for a deep target...at least that's my thought process and hunting strategy.

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The chirps are probably iron in the area along with other higher conductors. If your getting a lot of iron grunts, smaller dd's will give you more chirps but even with the quickest recovery speeds dd coils still can mask out. Concentric coil might be a better option. I sold my 9x12 concentric I had on my AT Pro to my buddy that has a Max and it works well and though your not going to get an accurate id on the target if in the same hole as an old iron nail the target will give you a better id and you should be able to trim out the iron. I think the smaller of the concentrics is lighter and has a smaller footprint so should do better in trashier areas.

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1 hour ago, kac said:

The chirps are probably iron in the area along with other higher conductors. If your getting a lot of iron grunts, smaller dd's will give you more chirps but even with the quickest recovery speeds dd coils still can mask out. Concentric coil might be a better option. I sold my 9x12 concentric I had on my AT Pro to my buddy that has a Max and it works well and though your not going to get an accurate id on the target if in the same hole as an old iron nail the target will give you a better id and you should be able to trim out the iron. I think the smaller of the concentrics is lighter and has a smaller footprint so should do better in trashier areas.

Are you saying that a concentric coil can handle trashier sites better than a DD coil? 

Or are you saying that a concentric coil can handle good targets mixed in with iron targets better, even when the iron trash is located close to the good targets that might otherwise get masked out?

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Concentric coil will reveal a target mixed in iron where a dd will only report iron. As an example on my Tejon I will set my discrimination to break on an iron nail and if there are silver or copper coins in the mix I can still hear them. On a VDI machine the ID#'s will be lower on those targets but you can still ignore the iron.

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9 hours ago, kac said:

Concentric coil will reveal a target mixed in iron where a dd will only report iron. As an example on my Tejon I will set my discrimination to break on an iron nail and if there are silver or copper coins in the mix I can still hear them. On a VDI machine the ID#'s will be lower on those targets but you can still ignore the iron.

I think I see what you're getting at. Let me use some examples to see if I'm understanding you correctly.

Scenario 1: an iron target next to a silver coin and you're using a DD coil - if the coil and metal detector don't have the ability to separate the coin from the iron, the iron will mask the coin. If in zero discrimination mode, you'll hear iron. If in discrimination mode to only hear/see silver coins, you'll hear/see nothing at all.

Scenario 2: an iron target next to a silver coin and you're using a concentric coil - if the coil and metal detector don't have the ability to separate the coin from the iron, the iron and coin targets will "average out." So If in zero discrimination mode, you'll hear a tone or see a VDI that indicates a mid-conductor (give or take). 

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Yes. I believe what happens is a concentric coil envelops and combines the targets so when targets occupy the same space the lower conductor will drag the higher conductor down. Much like audio where the bass can drown out or reduce the treble.

A dd coil works different where the signal is vertical so targets on top will block targets below.

Between the 2 concentrics that Garrett has for the AT series the 9x12 is ok in open areas with low to moderate trash. It has some descent depth, bit more than the stock dd by just a bit nothing to brag about. It is also a little heavier than the dd.

The smaller 6x9 concentric will do well in high trash areas but will have same or less depth than the stock dd. Smaller DD may work well in wooded areas as it is smaller and easier to work around obstuctions.

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