But.....How Deep Is That Metal Detector?
First of all, it's very difficult to answer that question, if not impossible. The answer really is "it depends"
The following all play a significant role, and in combination will always give varying results:
-size of a target-> the larger the target, the deeper a target can be recognized.
-conductivity-> aluminum vs. copper vs. gold. vs. iron vs. silver. Some rings, with size & mass being equal can be detected deeper then others.
-size of coil-> general rule says "larger coil = deeper depth however, add a lot of conductive particles, metal junk and high mineralization to the matrix, and the large coil becomes redundant.
-type of coil-> DD vs.concentric vs. mono. Each coil has a definite advantage over the other under different conditions
-frequency of signal from coil-> higher frequency usually (but not always) is more sensitive to tinier objects.
-VLF vs. Pulse Induction-> Pulse induction can easily pick up a dropped mini or gold ring with a medium sized coil 15-20" whereas a VLF might get about half that all other things being equal.
-Humidity, moisture in soil, orientation of target to the coil
--ability of the to perceive the receiving frequency from a coil and distinguish it's conductivity, depth, size etc.
-operator - properly setting up the electonic components based on knowledge and experiences
There are many more variables in involved affecting depth.....the above are just some of the more obvious ones. So really, YOU need to figure out what you are looking for ie. relics vs. jewelery vs. common coins vs. deep copper/silver coins. You also need to know the soil conditions and other factors in YOUR area where you are going to hunt. Lots of electronic interference from above ground or below will make some of the most expensive machines useless, unless you turn the sensitivity way down, which often times reduces your depth considerably. Same goes with extremely high mineralization like in Australia or red clay oxidized clays in North America areas. VLF may really struggle under these conditions, yet a PI (pulse induction) will punch down deep with no trouble.
Why should depth not be the most important factor for purchasing a metal detector? Because depth is only relative to certain conditions. Most targets are in the top 6 inches anyway, so why do you need to go down to 15-20"? In places like salt water or areas with a lot of deep junk rusty targets, the large coil on your $1,500.00 machine is practically useless, and when set up to it's maximum potential in these areas, will only give you say 4-5 inches. If somebody is trying to sell you an expensive detector, that they say is the deepest machine, you had better turn around and run fast....as that equates with someone trying to sell you a a parcel of land in a swamp. There is no 'DEEPEST" machine....it simply doesn't exist. But there are BEST configurations of a metal detector type for any given matrix of soil.
Choose wisely!
