HOW DEEP WILL IT GO?

This is another most frequently asked question.  It is also one without any single, clearcut answer.  Not being particularly savvy in the field of electronics, I’m not really the best one to discuss technical issues, but I’ll have a go at some of them.

There are a number of factors that affect detection depth.  The first is the size of the searchcoil.  Generally speaking, the bigger the coil is, the deeper the signal will go.  The next is the size of the target being detected.  A standard 8 or 9-inch coil might only detect a coin sized target to about eight or ten inches down, but it might detect an aluminum can at sixteen inches and a large metallic target like an underground tank as much as two feet deep or more.  Another factor that affects the performing depth of a detector is the mineralization of the soil.  In highly mineralized soil, depth might be quite adversely affected.  The sensitivity setting of the detector also affects depth, of course.  The higher it is set, the more sensitive the detector will be, and therefore the deeper it will detect buried objects.  However, if the sensitivity is set too high for the soil conditions, false signals may occur.  

So how does one choose the correct coil, and what’s the right sensitivity setting?  The sensitivity thing confused me at first.  The owner’s manual of one of my detectors put it this way: your car might be capable of going a hundred miles an hour, but that doesn’t mean you’d want to drive it at that speed everywhere.  I will generally run the sensitivity of my machine as high as it will go without starting to chirp, crackle, or chatter with false signals.  (In our forgiving coastal Georgia soil, that’s usually somewhere between 75% and 90%, but on our salt water beaches, a significantly lower setting must be used.)  

As to the searchcoil, there are small, medium, and large ones, to put it very basically.  Since the size of the coil affects depth,  why wouldn’t one just use the largest possible coil all the time, you ask? 

Larger coils tend to bigger than ten inches in diameter, and while they do detect much more deeply, they can make pinpointing more difficult.  They have more difficulty recognizing and separating multiple targets that are buried close together.  They are also a bit heavier and more unwieldy to swing around for extended periods.  

Small coils with diameters of four or five inches give less depth but are more accurate, and are sometimes called “sniper” coils for this reason, since they are used for shooting between closely-buried targets in heavily-trashed areas with increased accuracy and target separation.  So what’s the best size coil to use? 

Most often, it’s the medium-sized standard coil that provides the best compromise between depth and accuracy.  A good standard size coil for coinshooting is between eight and ten inches in diameter.  The standard coil covers most areas well, but if you have a smaller accessory coil you can put on and use in those really trashy spots, it can be a big help.  Similarly, if you are on a sparsely-targeted site where you’ll be searching for deep, old coins and relics, and you’re likely to be digging every signal anyway, then putting on a big accessory coil for added depth might be a good thing.

If you don’t have multiple accessory coils for your machine, however, don’t fret-  the standard coil with a 7-9” diameter that most detectors come equipped with might be the only coil you really need.  In most areas, it’s big enough to find some deeper, older targets, yet small enough to still be accurate.