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"4 Apex devices and 4 different search coils."

April 26, 2021 11:54AM avatar
As we all learned through the years, detector selection can be a very important task to take on as we try to match a unit or two to our types of sites, and make a good 'fit' for us physically. Equally important is search coil selection. We need one or more coils to better handle the different site environments we encounter. and make sure it works satisfactorily on the detector-of-choice.

We used to rely on using analog circuitry designed detectors, and progressed to some blended analog / digital deigns until today when almost all detectors made, that feature a visual display and tone-based audio Target ID, are a digital circuitry design. That can mean requirements for the use of 'chips' and other components for tight tolerances, especially for the 'tuning' required in making detectors AND search coils. The older detectors could be a little sloppier and still be made to work. I think back to when I built my first two, in early '65 and again in '66 / '67, and those Metal / Mineral Locators were BFO's. Only a single coil winding is needed with a BFO and the wire-winding instructions were easy to follow to come close-enough for them to be tuned to work.

The early TR and TR-Disc. models required two wire-windings in the coil for Transmit and Receive. Thy needed to be properly wound and positioned or they would be 'out-of-spec', but detector and coil design was still pretty easy-to-do. I remember when I worked at Compass Electronics in '87 to '89 and John Earle, the design engineer, would refer to the equipment's digital display when he wound and tuned coils for the new Scanner series which were for their 13.77 kHz operating frequency. That was at about the transition era of going to more analog / digital design, then things got tougher.

For a very modern example, let's get to the current Nokta / Makro Simplex +. It is digital circuitry and operates at 12 kHz so it's a fixed frequency. They made it / designed it with a round 11" DD coil and, for quite a while, that was the only coil they offered for it. I would like to have seen a good smaller-size coil like the 5" DD I used on all their other models, and a mid-sized coil such as the 5X9½ DD. Finally, after a long wait, they did offer a round 8" DD and an elliptical 5X9½ DD, but nothing smaller. The explanation was they couldn't design one to work with the Simplex +, and that had to relate to a 'chip' in the coil or in-line circuitry.

We heard announcements by Detech and NEL, both aftermarket search coil makers, that they would be offering coils for the Simplex +. I was informed by Delik at Nokta / Makro that they only provided 'chip' information to Detech, and only for their larger-size 13" Ultimate coil. She said we probably wouldn't see anything from NEL because they didn't share the Simplex + 'chip' information with them. Thus, it would be difficult to make proper coils. Minelab users also know aftermarket coils for their devices are also limited or restricted to those who they share specific design info with.

That brings us to detector design and how the visual Target ID works with a numeric VDI read-out, combined with an audio Tone ID that is associated with the numeric reading of a detected target. With multi-tone models, such as the 5-Tone Garrett Apex, the audio 'break-points' are associated with specific targets, and design tolerances, coupled with how well the search coil is designed, means that a coin, for example, will usually fall within a certain VDI range. Perhaps ± 1 or 2 numbers from a 'proper' read-out. If the design isn't proper, and here I am back to referring to search coils, we could have errant VDI read-outs as well as that shifting the audio response into a different, adjacent Tone ID range.

Okay, now we'll get on to my search coil testing of 4 coils, each used on my 4 different Apex devices.

Let me describe the detectors first:

► I purchased these in order of Apex #1, my primary-use device that I keep a 'Ripper' coil mounted. Apex #2 I bought to keep the bigger-size 'Raider' coil mounted. Apex #3 was because I got a NEL 5" DD provided by NEL for evaluation, and finally Apex #4 to have on-hand with the standard 'Viper' coil to use as a 'loaner-unit.'

► All 4 Apex devices have the same settings: Sensitivity at max; Volume at '8'; Iron Volume at '2'; start-up is Simultaneous 'MF'; Frequency Offset is '5'. The Mode is 'Custom' with th Discrimination set to accept from '20' on up.

► Apex #1 came with software version '.23' and Apex #2. #3 and #4 came with software version '.25' but ALL FOUR Apex devices now have the recent '.28' update.

Now for the search coils:

► The 'Viper' 6X11 DD is my 'original' coi that came with Apex #1 so it was an early release.

► The 5X8 'Ripper' DD and 8½X11 DD 'Raider' coils came directly from Garrett at the time they were first introduced.

► The NEL 5" 'Sharp' DD was provided by NEL at the time they first started producing coils for the Apex.

Now, for the comparison results:

I expected to see some sight tolerance differences when coils we switched to different detectors. This can be somewhat normal. I'll show the VDI results for the different models in order of search coil size selection. I used US coins for this test: 2-Nickels, 1-Zinc Cent, 1-Copper Cent, 2-Clad Dimes and 2-Clad Quarters.

5¢ coins: With Garrett's 5X8 'Ripper', 6X11 'Viper' and 8½X11 'Raider' coils I had VDI's of '52'-'53' from all four Apex's. Usually a '50' with the 5" DD NEL 'Sharp' coil.

Zn 1¢ coin: With Garrett's 5X8 'Ripper', 6X11 'Viper' and 8½X11 'Raider' coils I had VDI's of '75-'76' from all four Apex's. Usually a '70'-'71' with the 5" DD NEL 'Sharp' coil.

Cu 1¢ coin: With Garrett's 5X8 'Ripper', 6X11 'Viper' and 8½X11 'Raider' coils I had VDI's of '80'-'82' from all four Apex's. Usually a '77'-'78' with the 5" DD NEL 'Sharp' coil, but I did get an '81' with one of the Apex units..

Clad 10¢ coins: With Garrett's 5X8 'Ripper', 6X11 'Viper' and 8½X11 'Raider' coils I had VDI's of '80-'82' from all four Apex's. Usually a '77'-'78' with the 5" DD NEL 'Sharp' coil, although one of the Apex units did give a '79'-'81' VDI.

Clad 25¢ coins: With Garrett's 5X8 'Ripper', 6X11 'Viper' and 8½X11 'Raider' coils I had VDI's of '87-'91' from all four Apex's. Usually an '84' with the 5" DD NEL 'Sharp' coil.

So all of the coils worked and gave a good 'Beep' on all of the coin samples. Also, all of the coils, on all of the units, hit 7-out-of-8 on my Nail Board Performance Test, just to check on Iron Nail handling.

But if you look at the results you'll see the issues I had with the 5" NEL coil.

On all 4 Apex units the 5¢ coin had a slightly lower VDI read-out. The Zinc 1¢ also had a significant lower VDI read-out. Both the Copper 1¢ and Clad 10¢ pieces, with very similar conductivities, gave a notable lower VDI with the NEL 5" 'Sharp' coil that it dropped them out of the higher Tone ID and down into that for a Zinc 1¢. The Clad 25¢ coins also had a lower VDI read-out with the NEL coil, but at least stayed in the higher Tone ID range.

My Conclusions:

• Naturally, I will kep enjoying my Garrett-produced search coils, especially the 'Ripper' on my 1st Apex as a general-purpose set-up. The larger 8½X11 'Raider' will be at-the-ready on my 2nd Apex for any sparse-target open area searches. The 'Viper' coil will stay attached to my 4th Apex which is a 'Loaner-Unit'.

• I will be contacting NEL in the next day or so to ask if they have had other issues with the 5" Sharp coil, or any of the other coils they made for the Apex, and, if so, have they made some correction in their design so that they will now produce VDI and one ID responses similar to the factory-made coils?

• If they have, then I want to get another 5" 'Sharp' DD because they fit where I need them, and they otherwise work okay at finding stuff.

If I hear more reports about errant behavior with the NEL coils, or if they haven't made any corrections, then I'll likely let it go. At the same time I will continue to pester the good folks at Garrett about trying to make their own smaller-size coil, like the 4½" they have or maybe a 5", and especially try to configure a workable Concentric coil. That's what I would really like to mount on the working end of my 3rd Apex ... the one assigned 'small-coil duty'.

We are talking about now and into the future as Garrett has now brought us a SMF design, and can only move forward by improving the 'Apex' series and that means offering a good selection of search coils. I'm just glad to have their Apex w/MF and the option to select 5 kHz, 10 kHz, 15 kHz or 20 kHz whenever I feel it will be to my advantage. The Apex has been, and is, working well for me, and that's what is important. And I appreciate the fact that it is such a light-wight and easily-to-handle package. Great for my aching body.


PS: Sorry I didn't get this posted last evening but I was out detecting after dark and taking advantage of the Apex back-light. Very comfortable dark-o'clock weather in this chunk of Texas. Looking forward to reports from others about their Apex and coil performance.

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

Stinkwater Wells Trading Post
Metal Detector Evaluations and Product Reviews
I'm now 'back home' in Farr West Utah
monte@ahrps.org ... or ... monte@stinkwaterwells.com
Detector Outfit: A selection of my chosen makes and models, with the best coils mounted for the tasks I'll take on.
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"4 Apex devices and 4 different search coils."

Monte 728 April 26, 2021 11:54AM

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