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Spent the week with the 3 kHz coil

N

NH Bob

New member
Got out 4 times in a small field, each time with a different person with a different machine. I always boasted that the 10" DD was the coil of choice for open field hunting. I've changed my view on this and am sold on the 3 kHz coil.
Of the nine coins found, only 1 was found by another person with a different machine.
My first outing netted me these nice finds.
[attachment 124063 HAM09.JPG]
Second time out in the same field with another friend.
[attachment 124064 Ham092.JPG]
Third time out and I thought this was it for this small field so posted the group.
[attachment 124066 Ham093.jpg]
The group
[attachment 124067 Hamall.jpg]
Then today I decided to give it one More shot. I got another Merc and this
Sweet Standing Liberty Quarter.
[attachment 124068 SLQ1923.jpg]
I must say, this coil is a little touchy on the edges of iron, but nothing you can't get used to.
Give it a try and give it a chance I think you'll like the results.
 
I've been posting praise for the 3 kHz coil for over two years! In soil that can GB with a setting of 29 or higher, it is the best coil I've found for the X-Terra. I'm convinced that GB settings of less than 28 do better with the DD coils. But, as you've learned, the 3 kHz is an outstanding coil for those higher conductive targets. After you've initially located a target, if you wiggle that coil as you pull it toward you, the distinct audio (harmonic tones in multiple tone mode) will tell you if it is a good target or a piece of deep iron. Sure saves digging a lot of extra holes out in those fields! Congrats on some great finds! HH Randy
 
n/t
 
To what do you attribute the higher GB numbers setting the better the 3khz coil does. ????????????
 
Diggers posts on the 3KHz is what got me to buy one. It does have that funny little sound on iron.
 
It isn't just the 3 kHz coil. It is all concentrics vs DD coils. In moderately mineralized soils, I get more depth out of my 9-inch concentrics than I do the larger DD coils. My theory is that, if the mineralization is such that a proper GB setting gives you a GB number of 28 or smaller, you are best served with a DD coil. Simply a matter of design characterisitics in that the DD coil handles higher levels of mineralization better. Concentrics, by design, won't "compensate" for that high of level of mineralization. On the other hand, if the ground allows you to balance with a setting of 29 or higher number, it must have low enough mineralization that a concentric will work just fine. I don't have any scientific evidence of this. But over the past few years, I'm pretty well convinced I'm in the ballpark with those numbers. JMHO Randy
 
Great post Bob.
Seeing all the good post on the 3kHz coil will insure that I buy one in the near future. I haven't owned a detector to put it on till a few weeks back. It'll add a new dimension to the X-Terra's.
Mick Evans.
 
In thinking this out many times, I believe the DD sees less ground than the Concentric. Thus better GB
The soil I've been working in for these finds is running in the high single #s to low teens. So it's been a tad touchy but can be tolerated.
 
and hopefully something in it is beneficial.
Thanx to Digger for his knowledge on the subject as I have just started with the 3 kHz coil.
I have used it on 2 other occasions and took it off. It takes a little practice to understand the coil.
So give it time and you will like it too.
 
a few posts I've made over the past two years, concerning this very topic.......
http://www.findmall.com/read.php?55,624925,625228#msg-625228
http://www.findmall.com/read.php?55,615433,615537#msg-615537
http://www.findmall.com/read.php?55,575118,575188#msg-575188
http://www.findmall.com/read.php?55,513606,513711#msg-513711
 
Thanx Digger

Fisher used to state in their manual that an 8" coil will process about 1 gal. of dirt, where a 12" coil will process about 7 gal. of dirt.
The design of the DD coil should see less dirt in a given area than a concentric coil of the same size. This to me says, that is why a DD coil is more stable in mineralized soil.
This is not a fact but only what my limited experience is telling me.
Is this worth further discussion?? I can stand corrected.
 
The DD coil does analyze much less soil (at any one time) versus the concentrics. But it does so because the design of the DD coil is such that it actually cancels the effects of ground signals. In short, detector coils are comprised of two windings. A transmit winding and a receive winding. The transmit windings transmit an electronic field into the soil. Metallic objects in the ground create a distortion to the signal. And the detector recognizes that distortion and signals the operator.

Concentric coils have the transmit coil "around" the outside perimeter of the coil and a similarly shaped receive coil near the center of the coil. This arrangement allows for a large "detection field", which typically results in the greatest depth and the most sensitive of coil designs. The downside of this arrangement is that the large, sensitive detection field makes the concentric coils more suceptible to ground signals (interference). This can result in a huge loss of performance when used in highly mineralized soils. So it can be said that a concentric coil is more succeptible to ground signals due to the volume of soil it analyzes at any one time. This is due to the electronic design in that it simply has a bigger "detection" footprint.

The DD coil also has two windings. But instead of one of them being "inside the perimeter" of the other, they are side by side, and parallel to each other. The name DD represents how they would look if you took one apart. If it were an elliptical coil, the right hand half (transmit side) would represent a capital letter D. The left hand side (receive winding) would be the mirror image of the right hand side. Or, a backward capital letter D. Instead of the detection field running between the two windings, as on a concentric, it actually runs down the center of the coil, directly under where the transmit winding and receive windings overlap. That signal "down the center" is why so many consider the DD coil excellent at target separation. Anyway, with the positive detection field running down the center of the coil, the remainder of the coil acts as a negative (cancelling) field. That cancelling field is what allows the DD coils to analyze less soil, and operate more effectively in highly mineralized soil conditions.



HH Randy
 
Basically I was on the right track but without the technical stuff. Aside from that, you have made it much easier to understand. Thanx Randy
Bob
 
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