Mineralized Ground and coil quesions (a bit long)

[TURNMASTER]

OK, this AM I got in a couple hours. this is what I GB'd at:
With tracking on in an area that has been ploughed many times over the years, or so it looked.
Stock 7.5k CC got numbers that ranged from 15 to 19 on average with a few high spots that got to maybe 22. Targets (good or bad) were few and far between.
Same coil in the gravel parking lot registered 17.

Changed coils to the 5 X10 HF DD and picked up GB points in the lot maybe around 25 (I need to double check).
Before I went home I scouted out a more wooded area in the property and in tracking with the HF DD got much higher GB #'s into the low 30's. Until I hit a whole bunch of iron junk then back down to 17 to 20. Got out of the iron for a minuet and numbers returned to high 20's low 30's..

I have found this type of result with my Stock coil at other locations in the eastern WA area. Low ground tracking #'s seem to abound.

I have gotten numbers all the way up to the 50 range a couple times, but not usually and I have been trying to check them a few times on each time out.

So armed with this info what is next?
I am thinking about getting a 10.5 MF DD.
Would this handle the ground better than the MF CC? and would it hit deeper.
From using my 5x10 DD I have found DD (that one anyhow) to be easier to pinpoint with.
Are all DD coils mostly the same for pinpointing?
OR do I need a smaller coil for the trash - I seem to be able to pick through pretty well with the 5x10 DD- would I do that much better with a smaller coil?

Just for the record I am leaning heavily towards the 10.5 MF DD for the penetration and mineralization and silver the places I have been hitting are older for sure some date back to the late 1800's. YEAH that ain't that old for you eastern folk, but it is what we have out here and I am jealous.

ALL Opinions Welcome (I need the knowledge) Eastern WA and Northern ID encouraged to chime in on this.

HH
Jeff

 

[Digger]

The fact that your ground phase readings indicated more "mineralization" while hunting in iron infested areas stands to reason. Remember, the coil is telling the electronics what the soil composition is. Seeing all that iron oxide bleeding into the ground is bound to skew the analysis toward a higher mineralization. And getting a higher ground phase number with a DD coil, compared to a concentric at the same site, also makes sense based on the fact that DD coils are designed in such a manner that "ignores" a portion of the mineralization. Therefore it takes less "electronic compensation" to obtain a proper GB using a DD coil as compared to using a concentric at the same location.

My findings are that if I am able to properly set my ground phase at 28 or higher (using a concentric), the concentric will perform well. However, if the ground phase setting is a lower number than 28, the DD coils will provide better results. All DD coils basically pinpoint the same way. If you center the target under the middle "bar" of the coil, slowly drag the coil toward you, the target will be directly under the front tip of the coil as the audio response drops off. Smaller coils will separate targets better than larger coils. Smaller targets are more sensitive to smaller, shallower targets. And larger coils will typically obtain more depth than smaller coils. Although the 5 X 10 is about the same "width" as the 6-inch DD, I find the separation better with the 6-inch. As well, the depth of the 6-inch is as good as the elliptical in my neck of the woods. (Iowa)

In my opinion, there are more old coins still hiding out there due to target masking, opposed to being too deep for most coils. In fact, I would venture to guess that 95% of the coins you will find are within the top 7 inches of undisturbed soil. In plowed fields, all bets are off! Sounds to me that the 10.5 DD at 7.5 kHz might be a good choice for you in the situation you described. Especially since you already have the elliptical. But don't sell the performance of the 6-inch DD short! It's on my X-Terra anytime I get into a trashy environment. Pulling a dime at 7 or 8 inches is well within it's capabilities. JMHO

Here are some posts I made concerning that "ground phase number" of 28.....
http://www.findmall.com/read.php?55,999298,999347#msg-999347
http://www.findmall.com/read.php?55,886917,886960#msg-886960
http://www.findmall.com/read.php?55,886917,887023#msg-887023


HH Randy

 

[TURNMASTER]

Thanks Randy,

I think I may need BOTH coils (ok want does not = need). It would appear both coils could work well at different sites.

I think I may need a Physics degree to hang with this hobby. I read thru all the links you listed and their links, lots of info.

I will have to put more consideration into my next coil before I pull the trigger.

I am leaning towards the 10.5 MF DD though (for the moment). I do like the way my current DD locates - I rarely use pinpoint mode with it and if I have to it is most likely not a coin in the hole (so far). Both coils would the best solution.

Great Forum
Jeff

 

[Digger]

I've used all the coils available for the X-Terras. The only "head to head" that I can perform is by using the 6-inch coils, because the 9-inch are all concentric, the elliptical is DD and both 10.5 inch are DD. Keep in mind that my soil is considered moderately mineralized, with concentric readings typically in the mid 30's to high 40's. But if I had to chose between a concentric coil and a DD coil for the soil conditions you described, and could just have one, I'd opt for a DD. Simple reasoning that a DD coil will perform in any soil condition. A concentric coil will perform best in sites with moderate or minimal mineralization. In moderate soils around here, the concentric coils will hunt deeper than a comparibly sized DD. That is why I like the 3 kHz concentric for my wide open spaces. I use the 6-inch DD for trashy areas. Not because it is high freq. But because the DD coil separates targets better than a concentric. JMHO HH Randy