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Re: What should I use to look for deep silver dimes?

April 17, 2019 09:21AM
Rich, thanks for sharing your experiences. In my case, I've tried 9.5" coils and 15" coils and found no better depth detections in the soils I've hunted! I've primarily hunted the S.F. Bay Area and the Portland Oregon areas, with moderate mineralization. Oh, and one time, the OTTS went for a club hunt in Washington Park in Portland. I saw a guy go over some ground with a "WOT" coil, which I think is 18" diameter. He found nothing. I went over the same ground with a 4X6" "shooter" coil with my MXT and found a Wheatie at ~4"!

I made a slight error in my response to kickindirt. I should have asked where (more specifically, the level of mineralization) he hunts in. This makes all the difference in the world.

Mineralization conducts the transmit field of the detector (in a typical "VLF" or induction balance detector). It "channels" the field into a smaller volume beneath the coil. The more mineralization, the more detection depth is lost, because the depth of the transmit field is reduced. This is the main reason for the value of the pulse induction detector, which is effected by the soil to a much lesser degree.

I found this coil selection chart on the web at an Aussie site:

• Small jewelry (e.g., necklaces and thin gold rings) at 7 – 15 cm
• Big jewelry (e.g., class ring) at 15 to 30 cm
• Small coins (e.g., Ticky, 1 cent) at 10 to 15 cm
• Large coins: (e.g., Kruger pond, 5 shilling) at 15 to 30 cm
• Jam jar lid, bicycle licence disc at 22 to 40 cm
• Coffee can size at 30 to 60 cm
• Cannon shell, etc. at 60 to 90 cm

Note: 7cM = 2.8", 10cM = 4", 15cM = 6", 30cM = 12"

Medium Searchcoils
For general-purpose hunting, which typically includes coins and coin-sized targets, a medium sized searchcoil (8 - 9”) is the best choice. Because a medium sized searchcoil provides the best combination of magnetic field concentration, detection depth and capability to detect the greatest range of target sizes within the detection area, it is standard with most detectors. In addition, it's lightweight and easy to maneuver.

Speaking of George Payne, this from a paper he wrote on detector design:


"As most of you have observed a larger coil will pick-up more ground mineralization. Because of the coil size it is effectively closer to the ground than a smaller coil. Therefore, it may make more sense to use a smaller coil in high mineral. Keep in mind that a coil picks up the ground in a very non- linear way. Pushing the coil down against a high mineral ground may get you say 1/2" closer to the target. However, the increase in ground signal may be several times greater than a deep target's signal. In this case you would wind up with less sensitivity. For better results raise the coil 1 or even 2 inches and use a smaller coil in highly mineralized soils.

Here are some general design parameters for a coil:

Transmit Coil -- 25 to 30 turns of 22 gauge wire. Diameter 7 to 8 inches.
Receive Coil -- 200 to 300 turns of 31 gauge wire. Diameter 3 to 4 inches
Feedback Coil -- 6 to 10 turns of 22 gauge wire. Diameter same as receive.
Tank Capacitor -- 0.47uF"


The bottom line: The largest coil size you can use to detect a penny/dime, depends upon your soil. In moderate mineralization that I'm familiar with, 8" is about it. In air, or soil without minerals, a larger coil can get you more depth - until the size of the target becomes the limiting factor.
Subject Author Views Posted

Important Topic by George: Deep coin shooting with a concentric coil???

glabelle 282 April 16, 2019 06:50AM

Related Reference if you're interested -

UtahRich 158 April 22, 2019 11:47PM

Related Reference of interest? Well, I'm not, and I don't mind commenting on it, either.

Monte 149 April 23, 2019 07:55PM

Coils and Coins -

UtahRich 105 April 23, 2019 08:46PM

Re: Related Reference if you're interested -

glabelle 132 April 23, 2019 07:11AM

Coil Sizes and Depth on Coins -

UtahRich 117 April 23, 2019 08:40PM

Re: Coil Sizes and Depth on Coins -

glabelle 96 April 23, 2019 09:37PM

Coil Sizes and Depth on Coins -

UtahRich 88 April 23, 2019 09:44PM

Re: Related Reference if you're interested -

OregonGregg 111 April 23, 2019 05:45AM

Re: Related Reference if you're interested -

UtahRich 99 April 23, 2019 08:54PM

Pardon me George and others, but this is a great topic.

Monte 187 April 19, 2019 10:35AM

George, this is a great topic. Question for Harold,ILL

UtahRich 166 April 19, 2019 05:45PM

Comments for Rich (Utah) from Monte.

Monte 152 April 20, 2019 08:40AM

What is DEEP ? - Some Detecting Options

UtahRich 147 April 20, 2019 07:43PM

Re: What is DEEP ? - Some Detecting Options reply Rich Attachments

Kickindirt 131 April 20, 2019 09:12PM

Re: What is DEEP ? - Some Detecting Options

OregonGregg 130 April 20, 2019 08:06PM

Re: What is DEEP ? - Some Detecting Options

UtahRich 110 April 20, 2019 09:22PM

Re: What is DEEP ? - Some Detecting Options Attachments

OregonGregg 129 April 20, 2019 09:35PM

Re: Pardon me George and others, but this is a great topic.

glabelle 132 April 19, 2019 04:43PM

George, I'll respond to your 5-points.

Monte 146 April 20, 2019 05:42AM

In a nutshell . . . . .

UtahRich 104 April 19, 2019 07:48PM

Re: In a nutshell . . . . .

glabelle 132 April 19, 2019 08:42PM

Preferences -

UtahRich 97 April 19, 2019 11:48PM

A few last comments on coils and absolute depth Attachments

glabelle 141 April 20, 2019 09:24AM

George, a simple reason I described the 'cone.'

Monte 126 April 20, 2019 03:59PM

Adjacency - And why is that still there thinking

UtahRich 115 April 20, 2019 06:13PM

Re: Adjacency - And why is that still there thinking Great Post Richthumbs up

Druid 99 April 21, 2019 09:49AM

Re: A few last comments on coils and absolute depth

jmaryt 102 April 20, 2019 10:28AM

Re: Deep coin shooting with a concentric coil???

Kickindirt 154 April 16, 2019 06:46PM

Re: Deep coin shooting with a concentric coil???

glabelle 131 April 16, 2019 09:57PM

Balancing to ignore the ground?

Monte 133 April 20, 2019 09:22AM

Re: Balancing to ignore the ground?

glabelle 143 April 20, 2019 09:34AM

Re: Deep coin shooting with a concentric coil???

Kickindirt 127 April 17, 2019 11:05AM

Just a thought or two regarding coil size selection.

Monte 126 April 20, 2019 09:59AM

Re: Deep coin shooting with a concentric coil???

glabelle 144 April 17, 2019 04:13PM

What should I use to look for deep silver dimes?

UtahRich 165 April 16, 2019 10:20PM

Re: What should I use to look for deep silver dimes?

glabelle 137 April 17, 2019 09:21AM

Re: What should I use to look for deep silver dimes?

Harold,ILL. 152 April 17, 2019 08:06AM

Re: What should I use to look for deep silver dimes?

jmaryt 143 April 17, 2019 10:44AM

Re: What should I use to look for deep silver dimes?

UtahRich 162 April 17, 2019 04:12PM



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