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Why No Concentric Coils For The Recent Multifrequency Detectors?


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14 minutes ago, DOOGY-MD said:

Question to the Forum:

Can you miss more targets with a DD than a concentric coil, at the same reachable ground depths (say, 0-5")?

From my understanding, the answer is yes. Concentrics will sometimes "average" two signals (such as an iron nail and a coin) while a DD coil could miss both due to iron masking and insufficient recovery speed and/or target separation.

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18 minutes ago, mh9162013 said:

From my understanding, the answer is yes. Concentrics will sometimes "average" two signals (such as an iron nail and a coin) while a DD coil could miss both due to iron masking and insufficient recovery speed and/or target separation.

You lost me.  If a concentric averages that's really not much different than masking.  

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That being the case, then the ultimate weapon would be a waterproof pulse induction w/discrimination, VDI, notching, v- break, tone variety and a elliptical concentric coil?

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54 minutes ago, Chase Goldman said:

You lost me.  If a concentric averages that's really not much different than masking.  

If two different targets are detected by a concentric coil (like a nail and clad coin), the signals of each could be averaged. 

So let's say you've got your discrimination set up so only iron is eliminated. Then a concentric coil passes over a modern coin next to an iron nail. Assuming the machine/coil can't separate them, you might still get a signal from your machine telling you there's a target under the coil. But this signal will probably be some sort of average or blend of the nail and coin signals.

If a DD coil passes over those same 2 targets, AND the DD coil and machine can't separate them (and only iron is discriminated out), then you might get no signal from your machine.

This is why my Tesoros (with their concentrics) matched, if not exceeed my Equinox 600 when run with my modified Monte's Nail Board test.

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55 minutes ago, DOOGY-MD said:

That being the case, then the ultimate weapon would be a waterproof pulse induction w/discrimination, VDI, notching, v- break, tone variety and a elliptical concentric coil?

Not really, b/c DD coils have their benefits, such as in high trash areas and highly mineralized soil.

Also, I think elliptical coils sometimes get less depth than their more round counterparts (but have the same height).

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27 minutes ago, mh9162013 said:

If two different targets are detected by a concentric coil (like a nail and clad coin), the signals of each could be averaged. 

So let's say you've got your discrimination set up so only iron is eliminated. Then a concentric coil passes over a modern coin next to an iron nail. Assuming the machine/coil can't separate them, you might still get a signal from your machine telling you there's a target under the coil. But this signal will probably be some sort of average or blend of the nail and coin signals.

If a DD coil passes over those same 2 targets, AND the DD coil and machine can't separate them (and only iron is discriminated out), then you might get no signal from your machine.

This is why my Tesoros (with their concentrics) matched, if not exceeed my Equinox 600 when run with my modified Monte's Nail Board test.

DD coils will also average two adjacent targets. 

Put a nail on top of or next to a US dime.

In your scenario the Equinox will average the iron nail and non ferrous target when the center spine of the DD coil is parallel to the nail's orientation.  With iron rejected the Equinox will more than likely null when the center spine of the DD coil is perpendicular to the nail's orientation. 

Depending on the detector's iron filtering quality, using a concentric coil in your scenario the targets will give a good response and be averaged (if you have a display), partially broken up but averaged or nulled.

This is why most experienced relic hunters or hunters that detect in thick iron usually have all or most of the iron range target IDs accepted whether they are using a DD or concentric coil and why suspected borderline iron targets are approached from more than one direction when swinging a coil over them especially when using a DD coil.

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Ok, how about, a waterproof pulse induction w/discrimination, VDI, notching, v- break, tone variety with a round concentric coil and DD coil package?

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duplicate post

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8 minutes ago, DOOGY-MD said:

Ok, how about, a waterproof pulse induction w/discrimination, VDI, notching, v- break, tone variety with a round concentric coil and DD coil package?

Dream on......................

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Usually a concentric that has the same volume as a DD will have a little more depth. DD coils have a very narrow and directional null that help in high mineralization and trash as you can better isolate targets where a concentric's null is much wider and more apt to have multiple targets in the same null.

Null is the area where the Tx and Rx intersect. Any time a metallic object passes through the null it disrupts the signal and the machine will sound off. Little bit like feedback with a mic and speaker.

The null on concentrics is between the Tx and Rx, not the very center as most think. Why a shallow target can cause a double hit more than a dd.

Because the detection field is much larger on a concentric they can be noisy in high mineralization or perform poorly such as in the salt.

Monty's Nailboard test is a good example of what Jeff is saying.

As for Concentrics there are standard 2 coil types Tx outer with Rx inner (reverse wound) and Co-planer where the Tx and Rx are wound flat and the Tx has a reverse wide only around the Rx creating a forced and well defined null. My guess is it would do better in iron infestation than the others but in the case of analog machines may flatten the audio response. Co-planers are more difficult to make as I don't think you can machine wind them.

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