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Truth and fiction regarding search coil types

August 23, 2020 06:14PM avatar
If we run the clock back to the late sixties and up to like about 1970 - '71, most detectors were BFO or conventional TR types and discrimination was not in use, and there were different search coil types of different labels or descriptions that were basically a coplanar or concentric type, and in '71 when Compass Electronics started, they brought out the first Wide-Scan coils, also known as Double-D, for hobby consumer detectors.

They worked just fine, and in '71 & '72 I was using Compass, White's, Garrett and Fisher models in my outfit, and that meant I not only had slightly different circuitry design detectors, but definitely different search coil options.

All of them had their pros and cons, and I never had a problem using the Double–D coils in most any type of trash, to include bottle caps. But that was then and using conventional analog TR circuitry. When discrimination became popular with all the major manufacturers oh, it was used on most all of the detector models and at that time, which was mid-to-late 70s, they learn that the detectors with Double D coils did not handle discrimination as well as models with a coplanar or concentric coil.

Most detectors sold where Hobby and related for Coin Hunting or Beach Hunting and with discrimination most manufacturers went to concentric coils. A lot of models offered for electronic prospecting, now referred to as Nugget Hunting, we're offered with Double-D coils. At the time I still favoured concentric coils on the detectors I used for nugget hunting and they worked fine. Even some very popular nugget hunting units came with concentric coils such as the Fisher Gold Bug 2.

One issue we do have to consider as we address some problem trash like those pesky bottle caps, is not just the coil type but the circuitry type and how things are designed. Most of the modern detectors in perhaps the last decade have been or have been transitioning to digital circuitry. That can make a difference compared with a lot of the analog circuit remodels we enjoyed.

The other problem to consider is the frequencies that are used in more of the modern detectors, as well as the High Gain design to try and achieve better depth and sensitivity there is a trade-off that makes them have a bit more challenge with bottle caps and rusty tin.

So it's not really the fact that the coil might be a Doubl-D that is the main issue, it's the detector circuit redesign which involves the frequency used, a High Gain design all combined.

I continue to use EPR, short for what I named Edge-Pass Rejection, when I get into a typical iron infested site which includes picnic areas and other places where bottle caps are frequently discarded.

Most of the time it is a lot easier to do a quick EPR check using a concentric coil then a double d, but both coil types still work okay for that.

And while some Doubl-D coils on some detectors do demonstrate reasonably good discrimination and visual ID, a concentric coil is generally going to be more accurate.


"Your EYES ... the only 100% accurate form of Discrimination!"

Stinkwater Wells Trading Post
Metal Detector Evaluations and Product Reviews
monte@ahrps.org ... or ... monte@stinkwaterwells.com
Detectors: Fisher F5; Garrett Apex; Minelab Vanquish 540; Nokta / Makro FORS CoRe, FORS Relic & Simplex +;
Teknetics T2+; Tesoro Bandido II µMAX & Silver Sabre µMAX; White's XLT
Pinpointers: Pulse-Dive -- ProPointer AT .. Headphones: 'Hornet' & 'Wasp' -- MS-3 Z-Lynk -- ML-80 -- N/M Green Edition
Note: Detectors are listed alphabetically by Brand. Models are chosen based on search site conditions.
*** All working well today to make memories for tomorrow. ***
Subject Author Views Posted

heeeeellllpppp! Monte, what am i doing wrong with the SimplEx? Attachments

dixiedigger57 123 August 23, 2020 07:29AM

I like Monte's fact/fiction response

zincoln 75 August 24, 2020 08:27AM

just may have to change coils.

dixiedigger57 69 August 24, 2020 12:50PM

dixiedigger57, quick comments about coils.

Monte 73 August 24, 2020 01:18PM

Re: dixiedigger57, quick comments about coils.

SvenS 61 August 24, 2020 04:43PM

Re: just may have to change coils.

OregonGregg 64 August 24, 2020 01:00PM

Re: heeeeellllpppp! Monte, what am i doing wrong with the SimplEx?

WM6 68 August 23, 2020 10:00PM

DD coils love rusty beer bottle caps, your Tesoro with a concentric coil would be better thumbs up N/T

Hombre 60 August 23, 2020 05:11PM

Truth and fiction regarding search coil types

Monte 78 August 23, 2020 06:14PM

Re: heeeeellllpppp! Monte, what am i doing wrong with the SimplEx?

OregonGregg 78 August 23, 2020 04:49PM

It's not just the Simplex plus that has trouble.sad smiley

Monte 81 August 23, 2020 01:19PM

have noticed coil differences

dixiedigger57 67 August 24, 2020 06:36AM

Re: have noticed coil differences

OregonGregg 68 August 24, 2020 07:19AM

Have noticed sound differences -

UtahRich 57 August 24, 2020 11:33AM

Crown Capsi

UtahRich 85 August 23, 2020 11:48AM

Bottle Caps -- Detector & coil decisions based on site opportunities.

Monte 67 August 24, 2020 05:58PM

Re: Crown Capsi

Sodbuster 65 August 23, 2020 06:24PM

Re: Crown Capsi

Dan'o 73 August 23, 2020 01:08PM

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