To each his (or her) own. But here are my rules of thumb for chosing a coil....... Larger coils cover more ground with each sweep. Therefore, larger coils do not separate targets as well as smaller coils. In areas with heavy concentrations of targets (trash and/or keepers) I prefer a smaller coil. DD coils separate better than concentric coils, due to the field of detection. (blade vs conical pattern). So if I am hunting a site with multiple targets with each sweep, I opt for a small DD coil. DD coils are designed to perform better in areas with higher levels of mineralization. When I am unable to properly GB my stock 9-inch concentric at 7.5 kHz with a ground phase readout of 28 or more, I consider that to be in the area of "higher mineralization" and switch to a DD coil. Higher frequencies are best suited to identify targets with lower conductivity.(gold) And, lower frequency coils are better able to properly identify targets with higher levels of conductivity. (copper and silver) If I am hunting for small gold jewelry or gold, I'd opt for a higher frequency coil. On a wide open beach it would be one of the larger high frequency coils as they cover more sand than a smaller coil. If I am hunting for US coins, I opt for either the 7.5 or 3 kHz coils. If I am coin hunting a wide open area that is moderately mineralized, I put on the 3 kHz concentric. If it were a highly mineralized area, I'd go with one of the larger DD coils. If it is an area with multiple targets, like the local park, I use the 6-inch DD. Although I would prefer a lower frequency coil for coins, the only available small DD is the higher frequency 18.75. And I believe any tradeoff of using the higher frequency is worth it due to the ability to best separate targets. So the things to consider are the mineralization level, target concentration and type of targets you are wanting to best identify. With all that said, any of the coil frequencies will detect anything metal. Some just identify certain metals better than others. By searching this forum, you can find many posts about the benefits of using specific coils and the different audio response you might hear on different targets. But based on what you've told us so far, it sounds as if your first priority will be to get a DD coil of some size and shape. If you primarily hunt wide open areas, a larger coil may serve your needs. If you are hunting parks or yards with multiple targets per sweep, then I'd recommend the smaller 6-inch DD at 18.75 kHz. JMHO HH Randy
