I would like to ask about the coils on the x Terra. Three nine inch coils at different kHz ? one at 3k kHz, another at 7.5 kHz, and yet another at 18.75 kHz. Which one would you use for what purpose ? Is one better at finding coins and another better at finding silver and gold ? Is one better suited for Beach while the other not ? Then there is a 10x5 inch coil at 18.75 Can anyone tell us which coil would be better for what type of metal detecting?
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Different coils for x-Terra 70
- Thread starter Waterdog
- Start date
the lower frequency coils are better at detecting higher conductive targets, and larger/deeper targets. Higher frequency coils are more sensitive to lower conductive targets and are more apt to detect smaller targets. Generally speaking, smaller coils separate targets more readily, but don't hunt as deep as larger coils.
I use the 3 kHz and 7.5 kHz concentrics for most of my coin shooting. I don't hunt parks, and seldom hunt yards. I prefer to hunt old sites, for old coins. I've said many times that I would rather find a few old seated dimes or IH cents as opposed to finding a whole pocketful of clad and zincs. But, different strokes for different folks. Anyway, the reason I like the two lower frequencies is not because of any theory. I like them because I have found them to be more productive in the sites I hunt. Not that the 18.75 kHz isn't a good one. But I have found that when I hook up the 18.75 coil, the elevated sensitivity is offset by my having to lower the sensitivity setting on my detector.
When you consider that silver and copper are higher on the conductive scale than gold, combined with the fact that there are far more silver and copper coins lost than gold coins, I believe the two lower frequencies will maximize my chances of finding the coins I am searching for, in the sites I hunt. Between the two lower frequencies, I use to hunt with the 7.5 kHz coil all the time. Mostly because that was the first coil available when I got my X-Terras. But this past fall, I found myself using the 3 kHz more than the 7.5, due to the large amount of old iron trash (cut nails) in the particular sites I was hunting. Again, there is no scientific proof. But as one who hunts in the all metal mode, I honestly believe that I can separate the low tone made by an old nail from the high tone made by a silver dime, better with the 3 kHz coil. It seems that the low tone produced by the iron has a more narrow target response with the 3 kHz, than it does with the 7.5 kHz. With that said, in open locations without adjacent iron trash, I have found little (if any) difference in the depth of detection, or the separation characteristics, between the three coil frequencies.
As to the differences between concentric and DD coils, in similar sized coils, the electromagnetic field established by the DD coil is a narrower field than the broader field of the concentric. Although this is an over simplification, think of the concentric coil as producing a round electromagnetic field, the same size and shape of the coil, and penetrating straight down into the ground. As the signal is sent into the ground, it becomes narrower as it goes down. At a certain point, the signal will "run out", leaving you with an inverted cone shaped pattern of detection. In contrast, the DD coil produces an electromagnetic field centered around the center spoke of the coil. Running from the front tip of the coil to the rear. This pattern also penetrates into the ground straight down, but with more of a "front to back" pattern as opposed to an inverted cone. Kind of a windshield wiper blade effect. This allows the DD coils to be "hot" from front to back, without having to analyze as much ground surface (at any one time) as the concentric. This is one of the reasons that DD coils are better suited for highly mineralized ground than concentric coils. Just as with the concentric coil pattern, the DD pattern also "runs out" at a certain depth. Even though the DD coil may not go as deep as a concentric (in moderate or lightly mineralized soil), some believe the "front to back" pattern remains, to the full potential of the coil's depth capacity. This is one of the reasons that, on shallower targets, swaths taken with a DD coil may not have to be overlapped as much as required with a concentric coil.
Since my soil is lightly to moderately mineralized, and recognizing that I hunt for old silver coins in farm fields, I prefer the 3 kHz and 7.5 kHz coils. If my soil conditions were moderate to highly mineralized, or if I were hunting for gold jewelry in the park, or looking for a lost earring in someone's yard, I would chose the higher frequency coils. And, if I were hunting a beach, I would probably opt for 18.75 elliptical DD coil. The solid bottom would allow me to sweep over the sand with less gouging and bouncing. The DD design would allow me to concentrate the signal output directly into the sand. And, the higher frequency would be better suited for the gold jewelry left behind.
Don't get all caught up in coil frequencies. They each may have specific purposes. But, the frequency difference between the X-Terra's 3 kHz - 7.5 kHz - 18.75 kHz is not very big. Detectors specifically designed to find gold have a much higher frequency than 18.75 kHz. And, most relic machines have a frequency much lower than 18.75 kHz. I think the X-Terra addresses the demands of those of us who hunt for want the versatility to hunt for everything! Knowing the strong points (and short comings) of each coil design, and how a specific frequency responds to specific targets, is important in maximizing your potential for success. But more importantly, know how to set the operating parameters of your detector for any given location. HH Randy
I use the 3 kHz and 7.5 kHz concentrics for most of my coin shooting. I don't hunt parks, and seldom hunt yards. I prefer to hunt old sites, for old coins. I've said many times that I would rather find a few old seated dimes or IH cents as opposed to finding a whole pocketful of clad and zincs. But, different strokes for different folks. Anyway, the reason I like the two lower frequencies is not because of any theory. I like them because I have found them to be more productive in the sites I hunt. Not that the 18.75 kHz isn't a good one. But I have found that when I hook up the 18.75 coil, the elevated sensitivity is offset by my having to lower the sensitivity setting on my detector.
When you consider that silver and copper are higher on the conductive scale than gold, combined with the fact that there are far more silver and copper coins lost than gold coins, I believe the two lower frequencies will maximize my chances of finding the coins I am searching for, in the sites I hunt. Between the two lower frequencies, I use to hunt with the 7.5 kHz coil all the time. Mostly because that was the first coil available when I got my X-Terras. But this past fall, I found myself using the 3 kHz more than the 7.5, due to the large amount of old iron trash (cut nails) in the particular sites I was hunting. Again, there is no scientific proof. But as one who hunts in the all metal mode, I honestly believe that I can separate the low tone made by an old nail from the high tone made by a silver dime, better with the 3 kHz coil. It seems that the low tone produced by the iron has a more narrow target response with the 3 kHz, than it does with the 7.5 kHz. With that said, in open locations without adjacent iron trash, I have found little (if any) difference in the depth of detection, or the separation characteristics, between the three coil frequencies.
As to the differences between concentric and DD coils, in similar sized coils, the electromagnetic field established by the DD coil is a narrower field than the broader field of the concentric. Although this is an over simplification, think of the concentric coil as producing a round electromagnetic field, the same size and shape of the coil, and penetrating straight down into the ground. As the signal is sent into the ground, it becomes narrower as it goes down. At a certain point, the signal will "run out", leaving you with an inverted cone shaped pattern of detection. In contrast, the DD coil produces an electromagnetic field centered around the center spoke of the coil. Running from the front tip of the coil to the rear. This pattern also penetrates into the ground straight down, but with more of a "front to back" pattern as opposed to an inverted cone. Kind of a windshield wiper blade effect. This allows the DD coils to be "hot" from front to back, without having to analyze as much ground surface (at any one time) as the concentric. This is one of the reasons that DD coils are better suited for highly mineralized ground than concentric coils. Just as with the concentric coil pattern, the DD pattern also "runs out" at a certain depth. Even though the DD coil may not go as deep as a concentric (in moderate or lightly mineralized soil), some believe the "front to back" pattern remains, to the full potential of the coil's depth capacity. This is one of the reasons that, on shallower targets, swaths taken with a DD coil may not have to be overlapped as much as required with a concentric coil.
Since my soil is lightly to moderately mineralized, and recognizing that I hunt for old silver coins in farm fields, I prefer the 3 kHz and 7.5 kHz coils. If my soil conditions were moderate to highly mineralized, or if I were hunting for gold jewelry in the park, or looking for a lost earring in someone's yard, I would chose the higher frequency coils. And, if I were hunting a beach, I would probably opt for 18.75 elliptical DD coil. The solid bottom would allow me to sweep over the sand with less gouging and bouncing. The DD design would allow me to concentrate the signal output directly into the sand. And, the higher frequency would be better suited for the gold jewelry left behind.
Don't get all caught up in coil frequencies. They each may have specific purposes. But, the frequency difference between the X-Terra's 3 kHz - 7.5 kHz - 18.75 kHz is not very big. Detectors specifically designed to find gold have a much higher frequency than 18.75 kHz. And, most relic machines have a frequency much lower than 18.75 kHz. I think the X-Terra addresses the demands of those of us who hunt for want the versatility to hunt for everything! Knowing the strong points (and short comings) of each coil design, and how a specific frequency responds to specific targets, is important in maximizing your potential for success. But more importantly, know how to set the operating parameters of your detector for any given location. HH Randy