Do I Really Need More Than One Coil?

By Monte Von December 1998

This question we see asked on the various forums and, as a rule, the responders to such a post are experienced detectorists who almost always reply with a "Yes." Sadly, too many dealers are not serious detectorists and fail to stock assortment of optional coils. An even fewer number suggest them to customers, and that's really a shame. Now, if the answer to the topic question is "yes," then a second question might be either "Which one?" or "How many?" Finally, anyone considering such a purchase decision should ask a simple "Why?"

For years I have encouraged serious hobbyists to have (and use) at least two coils. My reasoning is somewhat counter to the manufacturer's 'logic' for their standard coils. Let me offer a brief view of what has been, and is currently, offered as standard or as an accessory coil.

Many of my earlier detectors in the 60's to mid-70's were supplied with 5" to 8" coils, and they generally worked just fine. Coins were quite plentiful and trash, as we consider it today, was minimal and the coils supplied worked quite efficiently. Besides, not all detectors offered coil interchangeability. In the late 70's and through the 80's many manufacturers, like Compass, D-Tex, Fisher and White's, settled on the 8" to 8-1/2"diameter coil as standard. Garrett, Gold Mountain and Teknetics chose the 7-1/4" to 7-1/2" coil size, with Garrett going to the 8" by the late 80's. Tesoro's choice through the 80's included models with standard coils of 7" or else the 8" or 8-1/2" size.

Seems like a battle cry of so many hobbyists was to "Give me liberty or give me depth!" To this the manufacturers appear to have switched almost all of their models to an 8" standard size by the late 80's, and White's introduced their newly designed 9-1/2" coil on their top-end models. The idea here was to try and satisfy the desires of some customers who asked for better depth. Coin quantities on and near the surface were thinning down at popular detecting sites and many thought that older coins would naturally be deeper, so they wanted more depth. (NOTE: We know that such a belief is not necessarily true, but that's a topic for later coverage!) Anyway, going from 7" to 8", or from 8" to 9-1/2" diameter coils, we gained a slight increase in depth on coin-sized targets with a standard coil.

One very important thing to remember, however, is that we already had the 'liberty' of choice by simply opting for larger accessory coil. Most manufacturers had optional coils of about 10" to 12-1/2" available and, depending upon the particular detector and coil design, using those coils might have resulted in an extra inch or so in depth on coins. Personally, the 10" to 10-1/2" coil, usually offered by those who manufacturers who had the 7" to 7-1/2" coils as standard, was my favorite optional larger coil and they made a good compromise.

Another important consideration is that at about this same time, innovations in the electronics of detector design reached what is considered by many to be the about the limit. What we generally see are changes or improvements in physical design, battery systems, target ID via audio tone or visual display, etc. In other words, we have had power potential during the last twenty years or so, and have been constantly refining how they work in the discriminate mode, and how they convey the gathered information.

A final consideration by coin hunters is the type and amount of conductive junk that began to litter our parks, schools and recreation sites, especially in the last thirty years. Pull tabs everywhere, in many shapes and sizes. Screw caps and bottle caps that are more conductive than earlier types. More foil candy and gum wrappers than we used to see, and foil condom wrappers we never saw! So while the typical sites were being depleted of their coin targets, they were being resupplied with overwhelming amounts of conductive junk.

I have always appreciated having at least two or three coils for a particular detector, and that included smaller coils of about 4." It's my opinion that a coil in the 4" range is almost a must today for the serious detectorist to have at hius/her disposal. While the standard coils supplied today combine with advanced circuitry to punch a little deeper in the discriminate mode, they also tend to have a greater electromagnetic field around them making operation close to metal objects (such as pipes, posts and fences) and in very trashy sites more difficult. Combining the power and electronic control of today's detectors with the performance of a smaller optional coil will often allow you to detect as deep or deeper than a stock coil while dealing with annoying trash more efficiently.

As for "How many optional coils?" you might want or need, that will depend upon the number of detectors you have, and the areas of interest and types of sites you'll encounter, such as coin in parks and schools, beach hunting or serious relic hunting. "Why?" you might want an optional coil or two is simply answered. You'll have and use certain coils to better tailor the performance of a unit's capabilities to the specific challenges of a site. Challenges such as abundant high-conductive trash, iron junk, dense brush or building rubble, larger or deeper targets, tinier items or maybe just difficult mineralization.

Since this Internet site is read especially by Tesoro & SHADOWx2 users, I'll address them last, but because many of us do have more than one brand I will share my thoughts on practical coil selection. With most brands of detectors, the entire line operates on a similar principle and most search coils can be shared from model to model. In some cases their will be "specialty" models, such as those designed for nugget hunting, which operate at a different frequency and cannot share common coil sizes. Then there is one current manufacturer who's coils interchange, but they have two distinct operating types of detectors to select from. All of this can become confusing for many, so you need to know what your manufacturer has available.

Looking at the five biggest names in detector manufacture today we note some interesting offerings. Minelab builds several models but very seldom do you hear of any model used for coin hunting other than the Sovereign series. The available coils are an 8" or a 10." There are only after-market accessory smaller coils available so the consumer needs to select an 8" or 10" depending upon the particular site they will be working most often. If they will encounter much trash, the 8" would be better, and it their interests are mostly for coverage and depth, the 10" might be the way to go. Garrett and Fisher have basically two or three series of detectors that use the same size coil, but they are not interchangeable between the particular series. For example, Garrett has the CX & GTAx series which use different coils than the Treasure Ace (and GTAx 400) models, which are also different from the GTI series coils. With most models the standard coil available is an 8-1/2" size, except the GTI's which come with a 9-1/2" coil. Optional round coils include the 4-1/2" and 12-1/2."

One noteworthy feature of the Garret coil designs, except for the 9-1/2" GTI coil, is that they are all solid-bottom designs and that makes them less difficult to use in brushy sites as the stiff weeds and twigs don't have a hole to pop through and interrupt a smooth and consistent coil sweep. I believe most coin hunters would be best served with the 4-1/2" coil to handle trashy sites. The 12-1/2" coil might gain some added depth on coins, but I feel it is too large for brushy or moderately littered sites.

Fisher's coil selection is a little more interesting. They have two popular series detectors. The "X" models and the CZ models. Most come with an 8" Spider coil as standard, but you cannot swap coils from one series to the other. Optional coils listed for the "X" series are a 3-2/4", 5" and 10-1/2" Spider coil. One drawback for some users of the "spider" coils is their very open design which tends to hang up when bushwhacking. The 10-1/2" Spider coil might be of use to a few users who search very open sites, such as plowed fields or beaches, but feedback from many suggests to me that the Fisher's, which are known for their very good depth of detection, do extremely well with the standard 8" coil. I have found this to be very true and have chosen not to get a larger coil for my CZ-7a Pro. If anything, the 8" produces such an electromagnetic field that I prefer it only for beach work, or maybe some very open, low-trash sites.

The dynamics of the CZ series and their 5" coil are such that that combination is actually preferred for most detecting applications. The 5" coil is solid so there is no interruption in brush, and it gets extremely good depth. This combination actually rivals the performance of much of the competition with an 8" standard coil! This is the coil of choice to work trashy sites and although it's size is good, the CZ's performance limits it's overall success in iron nail trashy sites.

White's has what I feel is one of the best product line offerings available and I will tell you why. They are the only current manufacturer to offer very advanced fast-motion type detectors, known for their ability to handle bad ground and excellent target ID qualities, as well as excellent slow-motion type detectors with quick recovery and very good performance in trashy sites. It's not that they have both fast-motion and slow-motion detector, but the added benefit that they all share the same search coils! About half of them come standard with an 8" coil and the other half come with a 9-1/2" coil. Optional coils include a 4" and 6", as well as the 8" or 9-1/2", depending upon which coil the detector is supplied with. I personally have little use for an 8" White's coil. The 9-1/2" is my pick for searching wide-open spaces or the beach, but most of my work with an XLT or Classic IDX is done with a 6" coil. I also like the 4" coil for the trashiest of sites where iron abounds or to work in and around brush and rubble. It doesn't seem like there is much size difference between the 4" and 6" when you look at them together, but actual field use reveals some pronounced benefits. The 9-1/2" seems to be a nice compromise as a deeper-coin coil over a larger coil in the 12" range as I have found many 12" coils to lose some small-target sensitivity. With the 4", 6" and 9-1/2" coils I am set for most any application with either a good slow-motion or fast-motion detector.

This brings us to the Tesoro product line. As we know, most Tesoro's are shipped with an open center 8" coil. I like the thickness (thinness) of the 8" but the open center isn't handy in some brushy conditions. The optional coils include a 4", 7" and 10-1/2". They have also offered the user 8-1/2" and 11" wide-scan coils but since most hobbyists are coin hunters and the concentric coils are better discriminators I prefer to address only the concentric types. I have one main objection to the 10-1/2" coil and that is poor weight and balance. They can work just fine, but because the mounting point is so far to the rear they can become "floppy" and annoying in the field. For deeper searches on larger objects they work fine, but I don't think they maintain very good small-target sensitivity.

Over a dozen years ago I preferred the 7" coil for most of my type of detecting as I worked a lot of ghost towns and they handled better in and around the rubble and brush than the 8-1/2" which was the option. I noticed, too, that they were quieter in the nail trash while still working through it well. When Tesoro came out with the 8" open center coils they were lighter and nice appearing, and they o okay in the same ghost towns, but I have stuck with the 7" design as they seem to be quieter. Less "ticky" in the iron. As a rule I would only use the open center 8" coil on the beaches, where I like it because it tends to suck to the sand than a solid bottom coil. Otherwise I have relied upon the 7" and 4" coils for virtually all other Tesoro work. The Tesoro 7" coil gets very good depth with just a slight loss as compared to the 8" coil. Then along comes Troy Galloway and his SHADOW concept. Still a Tesoro, the SHADOWx2's most noteworthy advancement was a redesign of the thin-line 7" coil designed for their water units. Eliminating the weighty epoxy and through reversal of the inner coil windings, Troy's idea and Jack Gifford's design talents have delivered to us a very unique and impressive coil. Nice appearing and lighter than a Tesoro 7", but with performance over that of Tesoro's offering such that it can rival the 8" coil for depth. I evaluated the stock 8" and a "Super 7 Inch" coil designed for the Shadow at both inland and beach sites in Oregon, as well as many urban and older sites in Washington, Utah, Nevada, Colorado and California only to find that if I limited my self to two coils for a Tesoro product it would be the Super 7 Inch Shadow coil and the 4" accessory coil for the more trashy sites. You'll note that most of my recommendations are for a smaller coil. To be honest, there have been a lot of people detecting for over a third of a century and the most commonly searched sites are thinned down. To that you must add the abundant high-conductive trash that has been littered at these same sites and it is obvious that smaller is most likely to be better. If working a large sportsfield for coins then a comfortable larger coil will have some benefits. If I had my wishes answered, Tesoro would work with Troy and combine ideas and availability, and some newer design. My wish would be to see Tesoro offer the Super 7 Inch coil in a white housing for their detectors, and since the S-7-I coil performs near to an 8" but is still thinner, lighter and smaller to fit tight places, I wouldn't mind it if they dropped the 8" and offered us a thinner larger coil in the 9" to 10" size. Nothing bigger. If equipped with a nice 9-1/2"-ish coil to compliment the 7" and 4" I feel the Tesoro line would be well rounded. Especially if it was of a thin, solid- bottom design.

Do YOU really need an optional search coil? If you have only one detector, I would say "yes" and suggest that you get with a dealer, hunting buddy or fellow club member to try some available coils and determine just which one you think might bolster your success. Try them in the field, if possible, or try to duplicate an actual field situation and see for yourself.

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