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George, I'll give some short replies.

February 22, 2020 04:37AM avatar
The theory was (previous post) the requirement for passing the "Plank" test is 1) Fast recovery speed 2) Small concentric coil.

1) Without fast recovery speed, the detector swung E-W is masked by the nails since it cannot recover to pickup the nickel in between.

2) Without a small CC coil, when swung N-S, the 2 iron nails mask the nickel, since the blade like field pattern of a DD picks up more of the iron than the more pointed field shape of a CC.

The AT Gold has fast enough recovery, and with the 5" CC, it can capture the nickel target when swept N-S, not being overloaded with the iron signal.
"Older "detectors, "medium age" detectors, "modern" detectors and "modern with digital circuitry" detectors, all using a Transmit/Receive principle and not a BFO or PI design, can all have their strengths and weaknesses Double-D and Concentric coils can also have their strong and weak performance abilities based upon:

1.. Size
2.. Shape
3.. How they work with the detector's cir5cuitry they are attached to.

And finally, differences in the individual performance of the detectors and coils is also dependent on the actual Test Sample and any variables. In the case of my Nail Board Performance Test, those are all of identical size and shape and placement of the Iron Nails and Coin. Anyone, anywhere can do the test and relate the detector and coil and settings as well as performance. The difference in that test is if someone makes a change in the tested Coin which could be larger or smaller, thicker or thinner, or a higher or lower conductivity level.

In this particular 'Test' that I call the 'Plank Board' I used two square Iron Nails and a US 5s Coin, and placed the Nails and Coin as close as I guessed they were in a similar test I saw on You Tube. Then, before I tried any detectors and coils on this set-up, I anchored the Iron Nails in place so that Nickel and Nails were always going to have the exact same orientation. Not be placed closer or farther apart, just a tough looking test that will always be the same challenge for anyone, any detector, any coil be it type or size.

I've seen the photo of your similar layout and I've seen Oregon Gregg's test layout, and now I've seen Kickindirt's layout (which looked like a rather generous in gap or spacing to mine) and all three are a little different. Placement, nails, etc. In that test, I can see or read what other's have for results, but I am curious how different detectors and coils will perform on my Test Sample.

Finally, there isn't a "blade-like" field or a "cone-shaped" or "pointed" field as some might picture. The EMF radiates out and around the Tx winding. Descriptions we use are referencing the "effective portion" of the generated EMF and not the "projected" field like many people imagine. Often it is due to errant descriptions they have seen in print. Jack Gifford of Tesoro and Charles Garrett of his company used some proper descriptions and artwork in their earlier publications that was correct.

I don't understand that, but the bottom line is instead of putting the nickel below a fixed 1x4 board, ~3/4" thickness, I simply pushed it down into the soil, until the detectors failed the N-S pass. That they can detect a good target 1/4" below 2 nails is encouraging.
Yes, it is encouraging, and that's why each of us, any individual, can do tests that we think might help us learn a detector or coil better, or gain an understanding of the abilities and limitations we face. The same with my method on placing the coin exactly below where it was on top of the board simply to learn more.

Very simply, the penny has less total metal than a nickel. As long as the discrimination has high resolution, the penny is a tougher target to hit in amongst trash. The half dime would be even tougher. The plank test is failed by both the Impact and AT Gold with the 1-5/8" nail spacing. It takes a spacing of ~2" before a penny is detected.
Yes, the Copper or Zinc Penny are smaller than the Nickel coin, but they are more conductive so that can also factor in depending upon all the variables. One is the detector's operating frequency..

Moving the nails got the the iron nails just enough out of the transmitted field shape that the detector could then "see" the good target.
Yes, kind of what happened, but different coil sizes and shaped can be over or more influenced by Iron Nails depending upon their placement. Note my Nail Board which is the reason why Nokta got the design engineer busy making a 5" DD for the Impact. Using the Half-Dime the Impact Pro Pack had the 4X7½ DD which performed terribly. The 5" DD brought the Impact up to just about on-par with the Relic w/5" DD

Funny you mention "another concentric coil". I'm investigating the possibility of making a concentric coil that is 3" or 4" diameter (since the mfrs. will not) Maybe better is the coaxial coil which has an even more "pointed" sensitive area. There are trade offs, of course. The smaller you make the detected area to get in between targets, the less area you can cover per sweep of the coil!
Only a few manufacturers ever made a 3" diameter coil or a 4" coil. Generally they just were not accept by many detector users.

About serch coils. I used to use some Garrett models and had their 4½ Concentric for them. Garret's always called it a 4½" Concentric but I never actually measured it. Search coil sizes have historically been the actual measurement across the diameter of the coil. Some manufacturers got a little goofy with their marketing folks using catchy different names, but it also hurt some of their sales. White's used the 6½" diameter housing of the Blue Max 600, which they called a 6 Inch coil even though it measures more closely to 6½ Inches, and renamed it 5.3 Black Max and then 5.3 BullsEye for the 6.59 kHz models. And 5.3 Eclipse for the upper-end higher-frequency models. All use the same 6½" coil housing.

Tesoro must have thought it was a cute idea and they named their new 6" Concentric coil a 5.75. In both cases, many consumers thought the coils were smaller, in the 5-something inch size, and didn't buy them.

You referred to the 5" Concentric for the Garrett sniper coil they call a 4½ Inch. Like I said, it's been many years since I had one around to measure. What is the measured physical diameter of that coil?

That would suggest that you have SOME coil there! The sharper (smaller) (more pointed) your detection area, the better you will be able to get in between targets. If your detection area is large, the detector will see many targets at once and will have a harder time discriminating between them.
Generally, and "in theory". that is kind of true. But there are many factors involved with a detector's circuitry and the projected area of different search coils.

That brings me to another point. Since all modern detectors use digital technology now, the ones with the best "target separation" will have higher resolution analog to digital converters. Typical A/D converters are 8bit, 10bit, 12bit, 16bit, etc. resolution. The higher the resolution, the sharper the ferrous/non-ferrous break point.
Kind of, but not always so. The Teknetics T2's have some of the fastest "separation" you'll find. Some others come close, but the T2 demonstrated "separation" to me after they came out in 2006. To demonstrate a detector's ability to 'separate' I have two 12" wooden paint stir-sticks, and fastened between them are 7 Trade Tokens. The 1st Token is positioned half-way on the ruler with the '0' line running down the center of Token. The 7th Token is at the far-end with the 12" mark running through the center of that Token. I then positioned the other 5 Tokens so the Inch 'mark' is running across their center-point at 2", 4", 6" 8" and 10".

All 7 Trade Tokens are a higher-conductive metal, all about the size of a US 5¢ piece, and all positioned so their centers are exactly 2" apart. That means there is very little distance or space between the edges of each metal Token. Using the motion-based Discriminate mode, and when hunting in dense Iron trash I favor the 2-Tone mode, then with the search coils about 1½" to 2" above the Tokens, sweep the coil right down the line and listen to each Token sound off. Slowly increase the speed and you can quickly count the 7 audio 'Beep' responses from each one. Very impressive demonstration of 'separation

But that means very little in high target-count areas IF there are any nearby masking targets that are ferrous, or if anything is being rejected. Why? Because the detector's circuitry also has to process a low-tone for Iron targets and an even greater rejection signal that has to recover enough to respond to a nearby Non-Ferrous object. Separation is very good when comparing a series of closely-spaced Non-Ferrous targets w/o any Discrimination or target processing in the circuitry. There's just a lot going on in detector circuitry and it varies from brand-to-brand or model-to-model.

Well, based on previous tests, I was looking for a machine that could best separate a good target with close surrounding iron trash. As stated above, the criteria was fast recovery time and small transmitted field area. The AT seemed to fit that. It passed the test! The other criteria that I'm acutely aware of is weight. The AT is light. The problem with the AT is balance. This can be addressed. I could hip mount it or build a shaft for it that balances.
Things get top-heavy, for me at least, with the AT design. I had an AT Pro to evaluate years ago when first introduced and it became fatiguing after I wasn't into the day's hunt for very long. I used to own and use a Garrett Scorpion Gold Stinger and it was also a bit top-heavy, but the control box snapped off the rod and could be belt-mounted quick-and-easy.

Okay when I used it for some urban hunting around the Portland metro area, but in the sagebrush and weed-choked old ghost towns I had to deal with brush snagging the coil cable between the handgrip and hip-mounted control housing. I didn't use that method long after that.

Also, I've got 3 silver dollars coming so I can test the "silver stack".
That will be interesting. I know I had some control of the GB setting for the motion-based Disc. mode on the Scorpion, but I'm not sure how the Garrett AT's are designed. You might be able to tell how it will do on the silver coin stack just by checking the manual GB over a very mineralized rock or typical black asphalt. Just manually adjust the GB for a very negative Ground balance in All Metal.. Quite negative. Then go into either of the Disc. modes and bob the search coil up-and-down, from 6" to 1". If the detector 'Beeps' on the uplift away from the ground, then the GB might be tied in and affecting the Disc. mode.

Monte, pass the test or not, I'd NEVER take your money. You have given us all so much. That would be stealing!
Well, I'm going to change my post and withdraw my offer. I know that Nail Test #4 is going to shock a lot of people, and I'm not going to give away the number of Iron Nails used, or the length or thickness. This is something I've encountered in old town sites through the years, and a few times in 'Lone Tree' here in Eastern Oregon. It is simply an example of what we might encounter and how an Iron Nail can impact a detector's performance in a heavily Nail Infested Site.

It will leave a lot of people scratching their head, but I am sure most folks who attend the WTHO and use their everyday detector choice with best settings for them to work those old townsites will not get a two-way decent response from the Nickel coin. I just double-checked last night and I have 3 or 4 detectors out of all those I have in my den or vehicle that DO hit on Nail Test #4 quite well.


"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
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*** All working well today to make memories for tomorrow. ***
Subject Author Views Posted

Updated test results, AT Gold added Attachments

glabelle 305 February 19, 2020 11:49AM

Stacked silver dollar results

glabelle 115 February 26, 2020 09:01AM

Good information. Were the Silver Dollars all

Monte 119 February 26, 2020 05:33PM

Re: Good information. Were the Silver Dollars all

glabelle 106 February 26, 2020 06:02PM

I haven't tried the AT Gold w/4½" Concentric coil.

Monte 121 February 21, 2020 08:45AM

I updated my above post and withdrew the money offer. N/T

Monte 106 February 22, 2020 04:46AM

Re: I haven't tried the AT Gold w/4½" Concentric coil.

glabelle 101 February 21, 2020 05:43PM

George, I'll give some short replies.

Monte 108 February 22, 2020 04:37AM

Re: George, I'll give some short replies.

glabelle 109 February 22, 2020 08:08AM

Back to you, George.

Monte 108 February 22, 2020 09:33AM

Re: Back to you, George.

glabelle 103 February 22, 2020 10:12AM

George, 'Rippville' is huntable!!

Monte 106 February 22, 2020 07:45PM

Re: George, 'Rippville' is huntable!!

glabelle 98 February 22, 2020 07:50PM

Yes, we get to control our time .... sometimes ....

Monte 102 February 22, 2020 08:43PM

Re: Updated test results, AT Gold added

OregonGregg 114 February 19, 2020 04:07PM

Re: Updated test results, AT Gold added

diggindeep 109 February 19, 2020 04:04PM

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