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j.t., just a brief comment about a 'detection field'.

October 21, 2022 12:21PM avatar
Quote
jmaryt
to be truthful?..all the time, especially with a small coil on board. with a "concentric" small coil design at least 50% because of "cone" search coverage from widest at surface to
narrowing of cone as search coverage goes deeper.

I want to respond here to clarify the comment because some readers can be, or have been, misled regarding a search coil's projected EMF and misbelieve it is in a 'cone' shape from a Concentric coil or a 'Knife-Blade' shape from a Double-D coil. I don't want folks to misunderstand your post. Neither of those is correct.

You did use the word "coverage' in your description and I prefer to refer to it as the 'reactive-portion' or 'responsive-portion' of the projected Electro-Magnetic Field. I have seen way too many sketches or drawing or heard descriptions mentioned that show or saw the detector se3nd out a "cone-shaped" signal from a Concentric coil, but the EMF actually is very tight with the lines of the magnetic field closest to the Tx coil, and as the distance from the coil winding toward the center-axis of the coil they get farther apart.

Equally as the field extends out from the side of the Tx winding they get farther apart. Due to the physical design of the Tx and Rx windings of most Concentric coils the distance from the Tx to Rx winding is uniform or consistent, and that results in a uniform EMF. If we picture a nice-and-proper round0shaped target, such as a US Coin, that is positioned 'flat' to the coil or horizontal on/in the ground, then the very uniform EMF of a Concentric coil will generally have the best depth possible for that target if it is in-line with the center-axis of th3 coil. In other words, 'dead center'.

That's the nice 'pinpoint' ability many of us have enjoyed for a long time using a Concentric coil for Coin Hunting. And the reason we can pinpoint 'dead-center' or, in other words get our deepest detection depth at the coil's center, is because that is the farthest distance from that particular coil where the EMF lines are still 'tight' and haven't bent or curved away. The tighter fields results in best depth and best pinpointing. Closer to the surface the strength of the field is strong and the lines are tighter so we 'see' a larger-size detection field closer to the coil, but as the distance to the weakest or farthest detection point increases, the 'responsive-field' is getting weaker as it weakens and THAT results in the 'reactive-portion' or 'detectable-portion' of the EMF is more of a "cone-shape" with a Concentric coil. It isn't the projected shape.

What about those Double-D coil designs? The ones that can annoy some of us in how they do or don't respond well? Well, things get a bit goofy due to the overlapping of the Tx and Rx winding and that they are rather stretched out to form the elongated overlapping 'D' shapes we refer to front-to-rear with those coils. Their functional field isn't as uniform as a Concentric coil, and they can behave differently with a left-to-right sweep compared with a right-to-left sweep on many targets. However, they still will produce their best depth-of-detection and most accurate Pinpoint and Target ID read-out on a horizontal coin in line with the center-axis of the coil.

In many cases, if viewed from thew size of the coil presentation, instead of a 'cone-shaped' responsive portion of the field it might be more of a 'bowl-shaped' reactive-portion, but nonetheless the best depth of strongest portion of the field does dwindle to a small area in line with the coil's center-axis.

Just wanted to maybe clarify some of the often mis-understood terms as it relates to a search coil's functional field-of-detection that is not a proper description of the actual projected EMF.

Now, here we were mainly discussion 'Overlapping' but for newcomers or less experienced to better understand what to or how much to 'overlap' they still need to understand what a detector's coil can provide them in the way of a functional detection field.

Monte

PS: Most know I am not an engineer but I am sharp enough to understand these tools, but if you question my comments, both Garrett and Tesoro used to show a proper EMF about a search coil, and you can contact a sharp engineer like Carl M. or read his works to get a nice, design engineer's explanation of what i am trying to describe.

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Subject Author Views Posted

When is it beneficial to Overlap Coil Sweeps?

UtahRich 330 October 20, 2022 11:38AM

How do you walk in a straight line?

GB_Amateur 201 October 22, 2022 10:15AM

GB_Amateur, your addition to this topic fits well.

Monte 187 October 22, 2022 02:18PM

Thanks, Monte

GB_Amateur 232 October 23, 2022 09:57AM

Great questions, Rich. thinkingconfused smiley

Monte 508 October 21, 2022 01:33PM

Re: When is it less productive to overlap coin sweeps?

Sodbuster 186 October 21, 2022 09:36AM

Re: When is it beneficial to Overlap Coil Sweeps?

jmaryt 465 October 20, 2022 06:10PM

j.t., just a brief comment about a 'detection field'.

Monte 170 October 21, 2022 12:21PM

Re: j.t., just a brief comment about a 'detection field'.

jmaryt 204 October 21, 2022 07:02PM

j.t., I agree about the 50% overlap coverage.

Monte 177 October 22, 2022 04:45AM

Re: j.t., I agree about the 50% overlap coverage.

jmaryt 182 October 22, 2022 07:54PM

hmmm . . . . .

UtahRich 194 October 21, 2022 08:41PM

Re: hmmm . . . . .

jmaryt 199 October 22, 2022 08:01PM

It looks like what?

UtahRich 229 October 22, 2022 09:46PM

Re: It looks like what?

Geotech 205 October 27, 2022 12:00PM

Re: It looks like what?

GB_Amateur 176 October 28, 2022 09:52AM

Re: It looks like what?

Geotech 169 October 29, 2022 01:54PM

Re: It looks like what?

GB_Amateur 189 October 30, 2022 09:38AM

Experimenting with your own equipment

UtahRich 192 October 28, 2022 10:42AM

Re: Experimenting with your own equipment

nwdetectorist 170 October 31, 2022 08:49PM

Rich, there is another way to deal with cell phone EMI.

Monte 208 October 29, 2022 10:43AM

Re: Rich, there is another way to deal with cell phone EMI.

jmaryt 164 October 29, 2022 07:20PM

Re: Experimenting with your own equipment

GB_Amateur 175 October 29, 2022 09:46AM

Re: Experimenting with your own equipment

Monte 188 October 29, 2022 10:52AM

Great response.

UtahRich 202 October 27, 2022 04:12PM

Re: It looks like what?

FeistyFrank 185 October 27, 2022 02:44PM

Re: It looks like what?

Geotech 186 October 28, 2022 10:15AM

Thank You, Carl.. Appreciated by many. N/T

Monte 145 October 29, 2022 10:54AM

Re: It looks like what?

FeistyFrank 170 October 28, 2022 11:10AM

Re: It looks like what?

jmaryt 172 October 23, 2022 07:52PM

Descriptions can be confusing. confused smiley

Monte 182 October 24, 2022 12:57PM

Re: Descriptions can be confusing. confused smiley

jmaryt 186 October 24, 2022 06:03PM

j.t., as UtahRich said ... No worries.

Monte 227 October 25, 2022 05:21AM

Re: j.t., as UtahRich said ... No worries.

jmaryt 272 October 25, 2022 05:07PM

Re: Descriptions can be confusing. confused smiley

UtahRich 188 October 24, 2022 07:54PM

Re: Descriptions can be confusing. confused smiley

jmaryt 193 October 25, 2022 05:13PM

Sunrise . . . . sunset . . . .

UtahRich 185 October 26, 2022 01:12AM

Re: Sunrise . . . . sunset . . . .

jmaryt 169 October 26, 2022 06:20PM

Or is that Snow Fal .... Snow Melt ....

Monte 167 October 26, 2022 01:29PM

A better description?

UtahRich 189 October 23, 2022 09:05PM

Rich, I am looking for Carl's post. N/T

Monte 195 October 23, 2022 07:09PM

Yes, the topic can create some interesting discussions.

Monte 189 October 22, 2022 02:35PM



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