For over forty-eight years I have preferred smaller-size coils for most of the places I like to hunt. By "smaller-size" I refer to those that were in the 4½ to 7" diameter, most of them being round shaped. As the years progressed the coil designs improved a little but the detector designs made very significant improvements and about twenty-thirty years ago I re-grouped my search coil assignment. Where 7" to 8" coils used to be 'standard,' by 1988 we saw the move in the industry to shift to larger-size 'standard' coils that measured in the 9", 9½", 8X9, 10", 10½" and 11" size, mostly round but some to the somewhat elliptical 7X11 to larger diameters than that. The bigger coils were, and are or can be, fine for larger, wide-open areas with very spread-out and minimal; trash. Beaches, big grassy parks, plowed fields and pastureland, etc.
As mentioned earlier, however, I have been spending the bulk of my search time in more crowded places, like dense woods or places with a lot of building rubble or sagebrush and other weedy vegetation. In addition to not much open space, the places I visit are heavily littered with ferrous debris, and some non-ferrous junk, but the iron contamination can be quite a challenge. For those places a smaller-size search coil is the absolute best when mounted to a detector model that is engineered to provide exceptional performance and unmasking abilities.
By my current coil descriptions I've relied on for the past few decades now, the "smaller-size" I am referring to are coils in the ±5" diameter to 6½" diameter, either Concentric or Double-D, whichever type and size provides the best in-the-field performance on the toughest iron trash challenges. Then for the fringe areas of those trashier placers, when the debris is less and more spread out, or for working many private yards or places like sports fields, I then like to select a detector with a "mid-size" search coil. And, to me, those would be a round-shaped 7" Concentric or an elliptically-shaped ±5X9½ DD, and of these coils I like an open-frame design, too.
I have found that in so many different hunt sites, these "mid-size" search coils provide impressive depth-of-detection and come very close to their otherwise 'standard' counterpart. They can actually have an edge in unmasking keepers near undesired trash, and also give a little tighter and better visual TID/VDI report on some of the mid-depth and deeper targets than a standard-size coil. So, enjoy that 5X9½ DD open-frame coil on your Anfibio Multi. It's a very good search coil choice for low to moderate trashy environments.
Monte
