So if ground balancing comes out at below 28 I'll use my 10.5" DD coil. How about using my DD in soil that GB's at let's say 40? I always here that a DD is better for soil that is highly mineralized but is it not just as good as a concentric in soil that is low in mineralization? The reason I ask is that the 10.5" DD is a larger coil & can cover more "open" ground then my 9" coils.
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Concentric or DD???
- Thread starter fdl
- Start date
Silverbackbob
Active member
Good question. You know, I've also heard that a DD coil is better in hot ground, but never that it is WORSE in good ground?? Hope someone with more experience will jump in here. I've also heard that concentric coils are inherently deeper and that DD coils seperate better. Nice to have both and to experiment I think. Good luck and HH. Bob.
bob.oz
Active member
I use the 5x10 HF DD at the beach all the time(dry sand only).....My GB is @ 30...The difference I see is TID's read higher,quarters hit at 44/46 but somtimes TID lower when the coil first hits on them,then get the higher TID after narrowing down the swing on the target.
The grounds I'm hunting now with the 9" concentric are a GB 29 and quarters are a dead on TID 42....Both coils work, just have to refigure the TID/tone info.
The grounds I'm hunting now with the 9" concentric are a GB 29 and quarters are a dead on TID 42....Both coils work, just have to refigure the TID/tone info.
When I came up with the theory about having a ground phase number of 28 as a "break-point", it was based on using the stock 9-inch concentric coil at 7.5kHz. If I were to check that same exact spot with a comparable sized DD, I would get a larger number. That is because the design characteristics of a DD coil will help neutralize the effects of the mineralization. So if you go along with what I've found, the number 28 is only a reference point when using the 9-inch concentric at 7.5kHz.
You should be able to get good results with a DD coil in any soil conditions. But if the soil is moderately mineralized (having a ground phase reading larger than 28 using the 9-inch coil at 7.5kHz) then you are not going to get as much depth as you would with a comparably sized concentric. Unfortunately, we don't have a DD coil the same size and frequency as a concentric, so it is difficult to prove. Having said that, I am convinced that any of the X-TERRA coils will detect anything metal. The differences between them are the accuracy of TID on specific targets, the stability of the audio response and likely how high you can boost your Sensitivity. Smaller coils do not have to analyze as much soil at any one time, so they can usually be tweaked a bit higher. Other than that, I believe a concentric coil will hunt deeper in moderately mineralized ground than a comparably sized DD. Larger coils will detect bigger targets at a greater depth than a smaller coil. Smaller coils are more sensitive to small, shallow targets than a larger coil. Lower frequency coils are more sensitive to higher conductive targets (copper, silver) than a higher frequency coil of the same size. Being more sensitive to those higher conductive targets, lower frequency coils will not lock on to higher conductive targets (gold, iron) as tight as the higher frequency coils. That is why I use LF coils in fields with deeply buried iron, as those type targets will jump around between FE -8 and CO 48, providing a harmonic blending of audio tones. Higher frequency coils are more sensitive to lower conductive targets than a lower frequency coil. And that is why the 18.75 kHz frequency is used for Prospecting. DD coils will separate targets better than a concentric coil. Smaller DD coils will separate targets better than a larger DD coil. To maximize the depth of your concentric coils, I recommend you overlap your swaths by 1/2, due to the manner in which the field of detection fades away. On DD coils, I recommend you overlap your swaths by 1/3. Although the DD coil does penetrate at a lesser angle than the concentrics, there is still some "front to back" fading of the detection field. JMHO HH Randy
You should be able to get good results with a DD coil in any soil conditions. But if the soil is moderately mineralized (having a ground phase reading larger than 28 using the 9-inch coil at 7.5kHz) then you are not going to get as much depth as you would with a comparably sized concentric. Unfortunately, we don't have a DD coil the same size and frequency as a concentric, so it is difficult to prove. Having said that, I am convinced that any of the X-TERRA coils will detect anything metal. The differences between them are the accuracy of TID on specific targets, the stability of the audio response and likely how high you can boost your Sensitivity. Smaller coils do not have to analyze as much soil at any one time, so they can usually be tweaked a bit higher. Other than that, I believe a concentric coil will hunt deeper in moderately mineralized ground than a comparably sized DD. Larger coils will detect bigger targets at a greater depth than a smaller coil. Smaller coils are more sensitive to small, shallow targets than a larger coil. Lower frequency coils are more sensitive to higher conductive targets (copper, silver) than a higher frequency coil of the same size. Being more sensitive to those higher conductive targets, lower frequency coils will not lock on to higher conductive targets (gold, iron) as tight as the higher frequency coils. That is why I use LF coils in fields with deeply buried iron, as those type targets will jump around between FE -8 and CO 48, providing a harmonic blending of audio tones. Higher frequency coils are more sensitive to lower conductive targets than a lower frequency coil. And that is why the 18.75 kHz frequency is used for Prospecting. DD coils will separate targets better than a concentric coil. Smaller DD coils will separate targets better than a larger DD coil. To maximize the depth of your concentric coils, I recommend you overlap your swaths by 1/2, due to the manner in which the field of detection fades away. On DD coils, I recommend you overlap your swaths by 1/3. Although the DD coil does penetrate at a lesser angle than the concentrics, there is still some "front to back" fading of the detection field. JMHO HH Randy
atomicscott
Active member
Can't say much that Digger hasn't said already! IMO, DD coils seem to be better overall. I know that in highly mineralized gold bearing areas of the desert here in SoCal, a DD coil is a necessity. DD's also seem to work just as well in lower mineralization as concentrics. Also, DD offers the increased ground coverage with only a very minimal loss of depth (in most cases). Concentric coils (on a vlf) don't do well in black sand/heavy mineralization and the max depth will be decreased to a much smaller area than on a DD coil.
Hi everyone....I'm playing around in my test garden,which consist of a quarter,dime & penny,with my 10.5" 7.5 kHz DD coil. How do I determine exactly where a coin is located under this larger coil? I think I read that it should be directly under the minelab label,but not sure. With my 9' concentrics it's easy for me to pinpoint,meaning I do not have to dig a large hole to find the treasure. If I'm on someones pretty lawn I don't want to be digging in the wrong spot.....Thanks.
Easiest way on a DD coil is to X back and forth over the target, and while doing so, slowly bring the coil back toward you while continuing to X. When the tone drops off the front edge of the coil, the target will be buried directly below that front edge. HH Randy
Mark in S.E. IA
New member
I only use the 10.5 DD 7.5 coil because the ground in my area for the most part is on the hot side, but when I do run in to those areas that have mild ground what I have found is that I need to swing a lil slower to help pick up the deeper targets. like a 4 to even a 5 second swing speed and I do feel that I do lose some depth with the 7.5 DD coil in real mild ground.
Mark in S.E. IA said:
Hi Mark....I'm really trying to get the hang of the 10.5'' DD & it seems that I need to lower the sensitivity, compared to the 9" concentrics, due to chatter & falsing(on the same soil).I do swing slower but I still get some chatter so I'm guessing this is one of the differences between a concentric & DD coil. So with a concentric(again on the same peace of ground) I'm able to jack up the sensitivity/swing speed. Just an observation on my part.
Mark in S.E. IA
New member
most times when I get too much chatter and falsing is when I am around power lines or swinging too fast and most times I run my Sen at Max or 1 or 2 numbers below max. Keep your swing speed at 3 to 4 sec, no faster then that.