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coils for X-Terra
- Thread starter bubber
- Start date
I've found the easiest way to read that chart is going by the colors. If you look down at the bottom of the chart, you will see the word WaterProof in blue. If you follow that line of blue writing to the right, turn up into a column at the arrow, and you will find either a blue Y or a blue N on each row. Those letters stand for Yes or No. So, if you find a coil you are interested in, go to the right and see if the blue letter is a Y or a N. That tells you if that particular coil is waterproof.
The next line has the red word Mineralized Ground. Again, follow that line to the right until it goes up into a column. Again you will see the letters Y or N. But in this column they are red. If the coil you are interested in has a red Y in the column, it is designed for operating in mineralized soil conditions.
The bottom line is Favored Targets. The first letter of each word is in pink. Those targets are Brass, Copper, Gold, Lead and Silver. Again, if you follow that line across the bottom, and go up the column on the right, it will give the initial of what that coil was designed to be best at finding.
[attachment 77289 8e_400x1000.png]
So lets take a look at the 6-inch DD coil. We can find it on the chart as the 5th coil down. 6"HFDD. That stands for 6-inch, High Frequency, DD. And below that we confirm that it is 18.75 kHz, high frequency. If we follow that line to the right, we can see that it is not shown in the column below the X-Terra 30. That means that this particular coil will not work with the X-Terra 30. However, it does appear under the X-Terra 50 and X-terra 70. Therefore, it will work well with the X-50 or X-70. Now, as we look further to the right, we can see that there is a blue letter Y, indicating it is waterproof. Next is the red letter Y, indicating it is designed for mineralized ground. And in the last column you have the pink letters BGL. That means that this particular coil is designed to provide excellent results on Brass, Gold and Lead.
In a nutshell... Any of the coils designed for the X-Terra are capable of detecting any metals. However, there are some design characteristics that may make one particular coil perform better than the others, in specific applications.
The 7.5 kHz coils are designed to work with all three models of X-Terras.
The 18.75 kHz coils are designed for the X-50 and X-70.
The 3 kHz coil is designed for the X-70 only.
All X-Terra coils are all waterproof except the elliptical, which is considered to be water-resistant.
Higher frequency coils respond best to lower conductive targets such as gold, brass and lead.
Lower frequency coils respond best to higher conductive targets such as silver and copper.
DD coils perform better in mineralized soil than concentric coils.
Larger coils provide more coverage and generally more depth than smaller coils.
Smaller coils generally provide better separation of targets.
The next line has the red word Mineralized Ground. Again, follow that line to the right until it goes up into a column. Again you will see the letters Y or N. But in this column they are red. If the coil you are interested in has a red Y in the column, it is designed for operating in mineralized soil conditions.
The bottom line is Favored Targets. The first letter of each word is in pink. Those targets are Brass, Copper, Gold, Lead and Silver. Again, if you follow that line across the bottom, and go up the column on the right, it will give the initial of what that coil was designed to be best at finding.
[attachment 77289 8e_400x1000.png]
So lets take a look at the 6-inch DD coil. We can find it on the chart as the 5th coil down. 6"HFDD. That stands for 6-inch, High Frequency, DD. And below that we confirm that it is 18.75 kHz, high frequency. If we follow that line to the right, we can see that it is not shown in the column below the X-Terra 30. That means that this particular coil will not work with the X-Terra 30. However, it does appear under the X-Terra 50 and X-terra 70. Therefore, it will work well with the X-50 or X-70. Now, as we look further to the right, we can see that there is a blue letter Y, indicating it is waterproof. Next is the red letter Y, indicating it is designed for mineralized ground. And in the last column you have the pink letters BGL. That means that this particular coil is designed to provide excellent results on Brass, Gold and Lead.
In a nutshell... Any of the coils designed for the X-Terra are capable of detecting any metals. However, there are some design characteristics that may make one particular coil perform better than the others, in specific applications.
The 7.5 kHz coils are designed to work with all three models of X-Terras.
The 18.75 kHz coils are designed for the X-50 and X-70.
The 3 kHz coil is designed for the X-70 only.
All X-Terra coils are all waterproof except the elliptical, which is considered to be water-resistant.
Higher frequency coils respond best to lower conductive targets such as gold, brass and lead.
Lower frequency coils respond best to higher conductive targets such as silver and copper.
DD coils perform better in mineralized soil than concentric coils.
Larger coils provide more coverage and generally more depth than smaller coils.
Smaller coils generally provide better separation of targets.
You are correct in that it does indicate that the 3 kHz concentric coil works well in Mineralized ground. But I will let BarnacleBill explain the particulars of his chart. I will say, however, that there are simply too many variations in mineralization, sweep techniques, preferred targets and site specifics to make a definitive statement as to which coil is "best" at any given site. This chart gives a good review of the X-Terra coils available.
My reasoning behind which coil works best & where, is based on my soil conditions. As such, it will likely be different than someone living in another part of the world. But around here, my thoughts are that DD coils perform better than concentric coils in soil conditions where your GB number is less than 28 on the X-70. That is an arbitrary number, based solely on my observations over the past couple years. In other words, if I hook up a 9-inch concentric coil and ground balancing it indicates a number less than 28, I usually switch to one of my DD coils. By design, the DD coils will help neutralize the adverse effects of mineralization and allow the detector to operate with more stability. Most of the places I hunt have what I consider to be moderately mineralized. In X-Terra terms, that means the numbers represented by my GB efforts are most always higher than 28. In fact, my GB numbers are usually always in the upper 30's to low 50's. For these soil conditions, concentric coils give me more depth of detection than their DD counterparts. So chosing between concentric and DD coils is not something I have to think a lot about. If all the X-Terra coil designs were available in all the frequencies, my coils would be 3 kHz. I hunt for old coins in old sites. I don't prospect for gold and I don't specifically hunt for small jewelry items. So, the ability to detect those lower conductive targets (with the 18.75 kHz coils) is not what is important to me. I not only like the 3 kHz ability to detect higher conductive targets (silver and copper coins) better than the 18.75 kHz coils, it also gives me a distinct audio report on ferrous targets. Although I get just as much depth and sensitivity out of the 7.5 kHz coils, using the 3 kHz allows me to hear (and ignore) those deep pieces of old iron more easily. Since the only coil that currently available in 3 khz is the 9-inch concentric, that is the one I use for most of my open field hunting at old farm sites and homesteads. But like I said, the 7.5 kHz goes just as deep and separates just as well.
Again, the chart is a good reference tool for determining the attributes of the various X-Terra coils. Which one(s) you chose will depend on your mineralization, the type of targets you are hunting for, the site terrain and your style of hunting. HH Randy
My reasoning behind which coil works best & where, is based on my soil conditions. As such, it will likely be different than someone living in another part of the world. But around here, my thoughts are that DD coils perform better than concentric coils in soil conditions where your GB number is less than 28 on the X-70. That is an arbitrary number, based solely on my observations over the past couple years. In other words, if I hook up a 9-inch concentric coil and ground balancing it indicates a number less than 28, I usually switch to one of my DD coils. By design, the DD coils will help neutralize the adverse effects of mineralization and allow the detector to operate with more stability. Most of the places I hunt have what I consider to be moderately mineralized. In X-Terra terms, that means the numbers represented by my GB efforts are most always higher than 28. In fact, my GB numbers are usually always in the upper 30's to low 50's. For these soil conditions, concentric coils give me more depth of detection than their DD counterparts. So chosing between concentric and DD coils is not something I have to think a lot about. If all the X-Terra coil designs were available in all the frequencies, my coils would be 3 kHz. I hunt for old coins in old sites. I don't prospect for gold and I don't specifically hunt for small jewelry items. So, the ability to detect those lower conductive targets (with the 18.75 kHz coils) is not what is important to me. I not only like the 3 kHz ability to detect higher conductive targets (silver and copper coins) better than the 18.75 kHz coils, it also gives me a distinct audio report on ferrous targets. Although I get just as much depth and sensitivity out of the 7.5 kHz coils, using the 3 kHz allows me to hear (and ignore) those deep pieces of old iron more easily. Since the only coil that currently available in 3 khz is the 9-inch concentric, that is the one I use for most of my open field hunting at old farm sites and homesteads. But like I said, the 7.5 kHz goes just as deep and separates just as well.
Again, the chart is a good reference tool for determining the attributes of the various X-Terra coils. Which one(s) you chose will depend on your mineralization, the type of targets you are hunting for, the site terrain and your style of hunting. HH Randy
Digger... thanks for the clarification. I wasn't finding fault with the chart, I was just looking for clarification, reason being that I thought that I understood from various sources that DD coils generally operate better in mineralized soil than the CC coils do. I also was under the impression that DD coils detected deeper, but I think I was wrong in that assumption.
I, based on my old detectors, thought that I should lean more towards a low freq (3 - 5 kHz), given that they will sniff out silver coins better. My main interest is in finding old silver coins. I won't be looking for nuggets and I don't anticipate doing much beach detecting. If I stumble across any jewelry, it will be by accident.
The only 3 kHz coil that would work for me was the 9" CC coil, but I was afraid of the mineralization issue. I don't know where you are from, but I'm in mid NC. Lots of mineralization. Therefore, I was thinking along the lines that maybe a better choice would be the 10.5" 7.5 kHz DD coil.
Would you recommend, given that my main interest is silver coins, that I go with the 3 kHz 9" CC and deal with the mineralization or the 10.5" 7.5 kHz DD coil which should handle soil conditions better?
Unfortunately, I've been into some "trashy" areas lately and almost everyone is recommending 6" coils.
Could use some advice.
Thanks,
Bob
I, based on my old detectors, thought that I should lean more towards a low freq (3 - 5 kHz), given that they will sniff out silver coins better. My main interest is in finding old silver coins. I won't be looking for nuggets and I don't anticipate doing much beach detecting. If I stumble across any jewelry, it will be by accident.
The only 3 kHz coil that would work for me was the 9" CC coil, but I was afraid of the mineralization issue. I don't know where you are from, but I'm in mid NC. Lots of mineralization. Therefore, I was thinking along the lines that maybe a better choice would be the 10.5" 7.5 kHz DD coil.
Would you recommend, given that my main interest is silver coins, that I go with the 3 kHz 9" CC and deal with the mineralization or the 10.5" 7.5 kHz DD coil which should handle soil conditions better?
Unfortunately, I've been into some "trashy" areas lately and almost everyone is recommending 6" coils.
Could use some advice.
Thanks,
Bob
You're thinking along the right track. Since you already have the X-Terra, you probably know about where the GB numbers have been, for the areas you hunt. As I mentioned, if the GB numbers are under 28 at those sites, I'd suggest the DD coils. You will obviously get more depth with the 10.5 DD at 7.5 kHz than you would with the smaller 6-inch DD. And, in my opinion, the 7.5 kHz provides more sensitivity on higher conductive targets than the 10.5-inch DD at 18.75 kHz. But you need to also think about the amount of soil (and targets) that the coil is analyzing at any given time. If the area is super trashy, (four or five targets per sweep) masking is less of an issue as the smaller coil will separate the targets better. Even though it is higher frequency than I typically use for silver and copper coins, the 6-inch DD at 18.75 kHz still finds them for me. I have found dimes at depths of over 6 inches with the 6-inch coil at 18.75 kHz.
Until Minelab comes out with more coil options at the 3 khz frequency, (and no, I've not heard that they will be) I'll keep using my 6-inch DD at 18.75 kHz to achieve the best separation. And since my soil (SW Iowa) doesn't warrant the design characteristics of the DD coil, I'll keep using my 3 kHz concentric for those less trashy areas. For my soil and the places I hunt, the concentrics do a better job for me. Obviously, your conditions are different and your choice of coils will likely be as well. But like I said, you are thinking along the right track. You just need to decide how big of a coil you can use effectively. JMHO HH Randy
Until Minelab comes out with more coil options at the 3 khz frequency, (and no, I've not heard that they will be) I'll keep using my 6-inch DD at 18.75 kHz to achieve the best separation. And since my soil (SW Iowa) doesn't warrant the design characteristics of the DD coil, I'll keep using my 3 kHz concentric for those less trashy areas. For my soil and the places I hunt, the concentrics do a better job for me. Obviously, your conditions are different and your choice of coils will likely be as well. But like I said, you are thinking along the right track. You just need to decide how big of a coil you can use effectively. JMHO HH Randy
The "penetration pattern" of the 5 X 10 elliptical DD coil you already have is very similar (in size) to the 10.5-inch DD that you are considering. So you are already able to accomplish much of what you are expecting from a 10.5, with the 5 X 10. With that said, the round coil does seem to have the edge on depth, compared to the elliptical. But they both cover just about the same amount of turf with each swath.
The reason I have the 6-inch DD at 18.75 kHz isn't because of the frequency. It is because of the smaller amount of turf analyzed at any one given time and separation characteristics. If the area you are wanting to hunt is as trashy as you indicated, separation is what you are lacking with a larger coil. And in that case, you would probably be better served with the 6-inch DD coil, regardless of frequency. It won't get the depth of the 10.5-inch DD or even the elliptical. But again, it doesn''t sound like depth is the issue for this application. If depth isn't the issue, you can already do most of what the 10.5 inch will do, with the 5 X 10 elliptical you already have. A bit of depth difference and target sensitivity differences, based on frequency. But many similarities as well.
Again, this is just my opinion, based on my observations. Your mileage may vary! HH Randy
The reason I have the 6-inch DD at 18.75 kHz isn't because of the frequency. It is because of the smaller amount of turf analyzed at any one given time and separation characteristics. If the area you are wanting to hunt is as trashy as you indicated, separation is what you are lacking with a larger coil. And in that case, you would probably be better served with the 6-inch DD coil, regardless of frequency. It won't get the depth of the 10.5-inch DD or even the elliptical. But again, it doesn''t sound like depth is the issue for this application. If depth isn't the issue, you can already do most of what the 10.5 inch will do, with the 5 X 10 elliptical you already have. A bit of depth difference and target sensitivity differences, based on frequency. But many similarities as well.
Again, this is just my opinion, based on my observations. Your mileage may vary! HH Randy
Excellent point, Digger... I was so wrapped up in finding similarities between the 5 X 10" 18.75 kHz DD coil and the 6" 18.75 kHz DD coil that I totally missed the similarities between the 5 X 10" 18.75 kHz DD and the 10.5 7.5 kHz DD coil.
Sounds like, once again the recommendation by popular (educated) opinion is the 6" 18.75 DD coil.
Thanks, again for your time and patience, in helping me understand this issue.
HH...Bob
Sounds like, once again the recommendation by popular (educated) opinion is the 6" 18.75 DD coil.
Thanks, again for your time and patience, in helping me understand this issue.
HH...Bob
BarnacleBill
New member
My decision to note the 3KHz for high mineral use is based on a couple of different factors. While testing the X70 with the 7.5KHz concentric, 3KHz concentric, and 18.75KHz elliptical coils on a saltwater beach with moderate black sand, I ran several trials involving ground balancing.
The X70 uses a computing engine of some nature to find the correct ground balance point during use of the Auto GB & Tracking GB methods. During these experiments I would manually adjust the GB to it's highest and lowest settings, and using a timer I would then engage Auto or Tracking functions and note how long it took the X70 to resolve the correct GB point. This is very easy in Auto mode because she will beep at you to tell you when she's done.
Of the three coils I had at that time, the elliptical HF was by far the quickest, and the 3KHz about 75% as fast when using the 7.5KHz concentric as the reference baseline. I spent well over an hour switching coils and changing locations on the beach, making note of my findings. This proved to me that the 3KHz was not that far behind in ignoring the conductive and magnetic matrix on this beach. The only kind of puzzling thing was why the salt didn't give the 3KHz more problems in that experiment.
In a later experiment using the ground signal reading ability of the X70, and testing soil which I then immersed in salt water mixed to the same salinity as ocean water. It became very clear that, the magnetic component strongly dominates over the conductive component of the salt. Therefore the mystery of why the 3KHz did so well was resolved for me at that point.
But since the above is just the experience of one individual on a forum, I have included below a section of the manual for a White's DFX, so that you can also see this is not any hype from Minelab, or the ravings of a metal detector lunatic.
"1 Frequency (3 kHz) - Operates at 3 kHz exclusively.
Provides for superior high iron mineral rejection
and depth when salt is not present. Also provides
for better depth on higher conducting metals such as
copper and silver alloys.
1 Frequency (3 kHz) provides an alternate search
mode when iron (without the presence of salt) is
extreme and the primary target is higher conducting
metals such as copper or silver. Some of White's
early 1970 models operated at 3 kHz and are still
revered for there performance in high iron black
sands."
HH
BarnacleBill
The X70 uses a computing engine of some nature to find the correct ground balance point during use of the Auto GB & Tracking GB methods. During these experiments I would manually adjust the GB to it's highest and lowest settings, and using a timer I would then engage Auto or Tracking functions and note how long it took the X70 to resolve the correct GB point. This is very easy in Auto mode because she will beep at you to tell you when she's done.
Of the three coils I had at that time, the elliptical HF was by far the quickest, and the 3KHz about 75% as fast when using the 7.5KHz concentric as the reference baseline. I spent well over an hour switching coils and changing locations on the beach, making note of my findings. This proved to me that the 3KHz was not that far behind in ignoring the conductive and magnetic matrix on this beach. The only kind of puzzling thing was why the salt didn't give the 3KHz more problems in that experiment.
In a later experiment using the ground signal reading ability of the X70, and testing soil which I then immersed in salt water mixed to the same salinity as ocean water. It became very clear that, the magnetic component strongly dominates over the conductive component of the salt. Therefore the mystery of why the 3KHz did so well was resolved for me at that point.
But since the above is just the experience of one individual on a forum, I have included below a section of the manual for a White's DFX, so that you can also see this is not any hype from Minelab, or the ravings of a metal detector lunatic.
"1 Frequency (3 kHz) - Operates at 3 kHz exclusively.
Provides for superior high iron mineral rejection
and depth when salt is not present. Also provides
for better depth on higher conducting metals such as
copper and silver alloys.
1 Frequency (3 kHz) provides an alternate search
mode when iron (without the presence of salt) is
extreme and the primary target is higher conducting
metals such as copper or silver. Some of White's
early 1970 models operated at 3 kHz and are still
revered for there performance in high iron black
sands."
HH
BarnacleBill
Bill... aha.. that's very interesting. Like I stated earlier, my first choice for coil frequency, based on my quest for silver coins, has always been for a stable 3 kHz coil.
Is sounds like the Xterra 3 kHz 9" CC coil might still work for me, in my red clay mineralized soil.
Thanks for your help.
Bob
Is sounds like the Xterra 3 kHz 9" CC coil might still work for me, in my red clay mineralized soil.
Thanks for your help.
Bob
Your DFX references may have proven that singing the praises of 3 kHz isn't just "any hype from Minelab". But seems to me that the jury is still out on "the ravings of a metal detector lunatic". Especially after learning that you actually tested "soil which I then immersed in salt water mixed to the same salinity as ocean water". 
Glad I don't live near the ocean. All we have are feed lots and hog yards here. Hmmmmm. do you suppose........... Nope! 
HH Randy
Glad I don't live near the ocean. All we have are feed lots and hog yards here. Hmmmmm. do you suppose........... Nope! HH RandyJackpine Savage
Active member
Haven't you ever gotten a target response in a Cow Pie? Now what do you do, that is the question 
Tom
Tom
(just kidding Bill) HH RandyJackpine Savage
Active member
are sensitive to foil?
Where's Jerry?
Just kidding of course. The stock concentric will pull small stuff quite deep as most know.
Tom
Where's Jerry?
Just kidding of course. The stock concentric will pull small stuff quite deep as most know.
Tom
Jackpine Savage
Active member
You just made me think of the "sail rabbits" in Return to Macon County.
Tom
PS: Never loan out your digging tools when field hunting!
Tom
PS: Never loan out your digging tools when field hunting!