Making Great Detectors Even Better
By: Andy Sabisch
Accessories to Improve Your Success in the Field
The focus of this article will be on a line of search coils manufactured in Bulgaria by Detech and distributed exclusively by Kellyco Detector Distributors under the EXcelerator and S.E.F monikers.
When metal detector manufacturers design a detector, they choose a coil that will work well under a wide range of conditions -in terms of ground mineralization as well as target concentration and depth. What experienced hunters have come to realize is that there is no one perfect coil for all conditions -at times a smaller coil will pull valuables from amongst trash a larger coil can't while at other times, a larger coil will reach targets that might otherwise have been missed. In addition, there are times when a Double-D design will work better than a concentric design. Adding additional coils to your arsenal will give you the flexibility to successfully hunt any site you might come across
Detech has been in operation for more than a decade and has become a well-respected designer / manufacturer of coils for a number of detectors. Their current lineup consists of more than 20 different coils using both the Double-D and concentric designs, with most being Double-D. Before discussing the performance of these coils, a quick overview of the two designs is warranted. A few years ago, the vast majority of detectors came equipped with concentric coils and many manufacturers did not even offer a Double-D coil as an option. This has started to change but even today, most detectors come standard with a concentric coil. The concentric coil has two circular windings -one slightly smaller and located inside the other -that send and receive the signal used by the detector to locate targets.
The Double-D's two windings are "D-shaped" and overlap in the center of the coil. The downside of the concentric design is that while targets on the surface can be detected across the width of the coil, the electrical field is somewhat cone shaped and covers less-&-less area the deeper you go. Without overlapping each sweep, you may very well be missing more good targets than you are finding. The Double-D design is sensitive the entire width of the coil -under the strip where the two coils overlap -and will detect targets under this entire area. The Double-D is also less affected by mineralized ground or black sand/saltwater. A final benefit is that unlike concentric coils, using a larger-than-stock coil will not result is a noticeable loss of sensitivity to smaller objects nor will going with a smaller-than-stock coil result in noticeably less detection depth. Based on these advantages, Detech's engineers worked on developing a line of Double-D coils that performed better than other available coils thereby maximizing the potential of the detectors they would be used on. The result was the line of EXcelerator coils first introduced nearly a decade ago which quickly gained a loyal following based on their in-field performance.
Not resting on their laurels, Detech worked on redesigning their coils and find a way to combine the best features of Double-D and concentric coils into a hybrid-type coil. After more than 3 years of research-&-development, the line of Symmetrical Electromagnetic Field coils -or S.E.F for short -were introduced. These coils were intended to provide more detection depth when compared to a similar-sized coil, better ground balance, improved stability and more accurate pinpointing versus other standard-design coils currently available.
Talking with JW at Kellyco to scope out this article, we settled on using the 10"x12" S.E.F. and the 6" Double-D & 8" concentric EXcelerator coils for my Minelab E-Trac & Explorer and the 10"x12" S.E.F coil for my Whites DFX. Testing would be done by selecting several areas based on the specific coil(s) I was testing and gridding an area using stakes & kite string. Hunting each area with a particular detector and the stock coil, all signals deemed worth recovering would be marked. Then, switching to one of the new coils, the process would be repeated -again marking any good signal. Finally, all detected signals would be checked with both coils before recovering the targets. This would allow any performance differences to be readily observable.
10"x12" S.E.F. Coil
The first thing one notices when unpacking the S.E.F coil is its unique design which explains its nickname -"The Butterfly coil". Being larger than stock coils from Whites or Minelab, the biggest advantage one expects is increased detection depth and more coverage with each sweep -both of which can improve your overall success in the field.
The first site I went to was a section of an older park in Charlotte that still turned up coins from the 1800's on occasion. Due to having been heavily hunted over the years, most of what remained was deep ... 7"+. Marking off two sections, I hunted both with the stock coils on the Whites DFX (9.5" concentric) and Minelab E-Trac (11" Double-D). The settings were those that I had found to be optimal for the area and in order to make the comparison meaningful, I would keep the settings there for the duration of the test. The initial pass through the first area using the DFX resulted in 7 promising signals being marked. Switching over to the S.E.F. coil, I re hunted the same area in the same direction to eliminate that variance being a factor. The same 7 targets were identified, but this time 5 additional signals were flagged. Switching back to the stock coil, I was able to get a faint response on 2 signals knowing they were there but not on the remaining three. The 5 targets produced 3 Wheat cents (1917, 1935 & 1937), an 1895 Indian Head and a 1926 Mercury dime with all being at least 8" deep.
I repeated this test at another section of the park using the Minelab E-Trac with similar results. Five targets were detected using the stock coil and 3 additional targets were found using the S.E.F. coil. The missed signals produced a 1906 Indian Head and two Wheats from the 1920's.
My impression of the 10"x12" S.E.F coils on both machines was that that they did provide the additional detection depth needed to reach targets just beyond the reach of the stock coils and that the response to these targets was more discernible even when I knew there was a target present. The slight increase in coil weight is more than offset by the increased performance the S.E.F. coils provide in sites that are not excessively littered with trash ...which leads into the next section of this article.
The 6" Double-D and 8" Concentric EXcelerator Coil
While the larger S.E.F. coils proved they can find coins deeper and handle mineralized ground better than stock coils, smaller coils also have their place in a detectorist's arsenal. There are countless valuables remaining in sites with a high concentration of trash and only a smaller coil can ferret the good signals from amongst the junk. Due to the overwhelming popularity of the EXcelerator coils, JW indicated that the 6" Double-D for the DFX was backordered so I used the coils I had available for this report.
Hardy Russell is a friend of mine that has recently started using the E-Trac and offered to work with me in trying the 6" coil out at some local sites. One was extremely trashy yet I knew still held some mid-1900's coins. As with the other tests, we started out by hunting a section with the stock coils on both the E-Trac and Explorer SE (10.5" Double-D). Both detectors really struggled in the trash and even with minimal discrimination, nulled almost constantly. Putting the 6" EXcelerator coil on both detectors, we re hunted the area and were amazed at the number of good signals. It was clear that most were in close proximity to trash. The results? A few clad coins with the stock coil ... and with the EXcelerator coils ... 4 silver dimes, a silver quarter, 9 Wheat cents and a silver bracelet.
On the way home we stopped of at a home built in the 1700's that had been very stingy with finds since we started hunting it. The small front yard was littered with old nails which resulted in almost constant nulling when hunted previously. Hardy switched to the 6" coil and almost immediately hit a good signal. The stock coil on my E-Trac did not produce a signal I would have dug, but wanting to see what Hardy had found, I started digging. After pulling the 3rd rusted nail from the hole, I was not overly positive about what was there when suddenly we saw a coin in the dirt pile .... an 1883 Indian Head! Not a bad find and one that had been in the same hole as several pieces of iron.
A few days later I took the 8" concentric coil (which is the only one made for Minelab FBS detectors) to some lots in a nearby town that were partially surrounded by a chain link fence. Working near metal such as fences, bleachers and parking meters is a bit of a challenge for a Double-D coil and I have found that having the concentric coil available was a useful option. Again, I hunted an area adjacent to the fence with the stock coil, and other than frustration, had nothing to show for the effort after 30 minutes of hunting. Switching to the concentric coil, the Explorer acted like a totally different machine. Keeping the coil just off the fence, I moved parallel to it and was able to recover 18 coins along the length of the fence line.
These experiences showed that the smaller EXcelerator coils provided better separation in high trash than the stock coil with better-than-expected detection depth.
The line of EXcelerator and S.E.F. search coils includes a range of sizes and configurations for models from Whites, Minelab and Garrett and greatly expands their versatility in a wide range of sites. All of the coils come with a one year warranty.
There are many different Excelerator Search Coil choices for owners of White's, Minelab, Garrett, Tesoro, Fisher, and Teknetics detectors, all have proven to be extraordinary in depth and sensitivity. All detectorists are looking to go deeper to find older more valuable coins. Excelerator coils make that possible. It takes only one "deep" find to pay for a search coil and perhaps a lot more left over. Investing in an Excelerator Coil can bring you exciting finds!