who bought the 11" X35 coil, I remain quite content just keeping and using my 5X9½ DD HF and 9" X35 search coils.
For over five decades of using so many makes and models of detectors and their standard and accessory search coils, I determined long ago that for my wants and needs in urban Coin & Jewelry Hunting, and especially for taking on ghost towns and other old-use sites that frequnty have densely concentrated areas of ferrous debris,, most larger-size search coils just don't prove out to be that beneficial. Back in the day when most 'standard' coils were 7" to 8" in diameter, I did use some 9", 10", 11", 12", 14", 15" and 16" diameter coils of both Double-D and Concentric design. Some of these were after-market coils but most were offered by the detector manufacturers, and I mean a lot of manufacturers.
I also evaluated search coils from three manufacturers when I was employed by one of them, mainly to disprove the wild claims the companies would make about improved performance. They had to be testing coil-to-car body and not coil-to-coin and ring sized objects. Some said going to a 12" coil would give them a 20% increase and a 14" to 16" coil might get them an additional 40% increase! Absolutely nuts! I designed a mechanical testing device to mount-and-sweep the coils and I used common US coins. I also worked with a couple of detector engineers to review my evaluations.
Naturally, we have seen come changes in the detector industry, such as most makes going to a larger-size 'standard' coil because too many people asked for, or claim they wanted / needed "more depth." That brings us to today when it seems most detectors come with a 9" to 11" search coil as a 'standard' size. Depending upon the particular coil size and coil type, and especially considering the particular make and model detector the coil will be worked with, going with any search coil larger than ±9" in diameter might provide slightly better side-to-side sweep coverage, but only slightly better. If a hunt site is relatively clean, being free of most ferrous and non-ferrous targets, you are likely to get a bit of an increase n larger-size objects, but generally little or no notable increase in detection-depth over a coil of about 9" in diameter. I am referring here to all these coils being round-shaped and not elliptical.
For example, with my ORX and the 5X9½ DD HF coil, I get very impressive depth-of-detection in larger parks when searching for coins and jewelry. Better than many competitor's detectors with comparable size coils. But I can use the same settings [size=small](other than Frequency)[/size] and mount the 9" X35 DD coil, and it provides even a bit better detection depth on those smaller-size targets. Thus, a coil comparison to keep elliptical to elliptical and round vs round for a fair comparison
I have talked with friends using similar detectors that I use and these are field-experienced detectorists, and generally we agree. I've done contract searches for a cache or other large object since the early '70s and for that I keep one detector at-the-ready. My Nokta FORS CoRe. Usually it only has the small 'OOD' mounted because I hunt densely littered sites, but when I want to go after a larger-size target, I mount the 13X15 DD on the CoRe. Otherwise, I do have the 11" DD on my Nokta / Makro Simplex +, but that's because they don't have any smaller coils yet. My most-used detectors, for hunting trashier ghost towns and homesteads, or old picnic groves, etc., or modern parks and schools and tot-lots where it gets trashier at times, all have smaller-than-stock coils mounted. From the 'OOR' DD to a 5" DD, 6" Concentric, 6½" Concentric, 7" Concentric, and for typical Coin & Jewelry Hunting locations with less trash to contend with I have my ORX w/5X9½ DD HF coil and another ORX w/9" X35 coil. Places like open grassy parks, sports fields, beaches, private yards, and other friendlier-to-hunt [size=small](less trash to deal with)[/size] sites.
For the ORX and Deus, I think these two coils cover the vast majority of needs we might have in coil selection. Just my biased opinion, but I found, and friends who tried the 11" agree, there really wasn't much of a benefit to the 11" coil, and it did make that nice, light-weight package a bit more nose heavy. Some felt the same as I found, that there was even a little loss in performance on smaller, thinner coins and jewelry. The smallest of the already small targets.
Monte
