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5x10" DD/HF Coil and the 6" DD/HF Coil - Visible Differences
Posted by: nero_design
Date: March 09, 2008 03:48AM
I started to write this Thread as part of an answer to someone else's question. However, I ended up writing more information than I expected to... and rather than paste this into the reply, I thought it would be better off to place these details in a separate thread.

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As someone who wanted to start out detecting beaches and occasionally go out the the Gold Fields, I seem to find myself doing things the other way around.
Prospecting has become my hobby now and I had to look at buying an additional coil or two on order to have any success.

There's three main coils to be considered in the High Frequency range for the X-Terra 70:
The 10.5" DD HF Coil (Better for beach and field but possibly not so much for Gold Prospecting for smaller nuggets)
The 5x10" DD HF Coil (Elliptical, Shaped to use in Difficult Terrain, Replaceable Skid Plate)
The 6" DD HF Coil (Super Sensitive/Waterproof/ NO replaceable Skid Plate)

It's my understanding that the DD High Frequency Coils are particularly good in the sort of mineralized soils that gold typically is found in.
I have the 5x10" DD HF and the 6" DD HF coils. Both are completely different to one another, even though they are both High Frequency DD coils. I imagine the 10.5 DD is also quite different although it was not recommended to me for Prospecting so I have not yet purchased one.


5x10" Elliptical Double D High Frequency (18.75khz) Coil:
The 5x10" is probably best for exploring areas where gold might be found. Larger signal blade means more area can be covered, especially the sort of iron-filled soils near where I detect. But this blade-like Emission Field is weaker, wider and a little shallower that I would prefer. It has a replaceable skuff cover but it's not water-proofed (for immersion) where the cable meets the coil itself. It has quite a wide field of detection near the coil (see the green Halo in the illustration). The blade area of the coil emission is a little broad compared to the 6" coil. The coil is sensitive to metal but NOT to really small nuggets (eg: smaller than 1/5 of a gram, if it's a few inches under the surface, probably won't register).



6" Elliptical Double D High Frequency (18.75khz) Coil:
The 6" coil is probably best suited to careful scanning of areas where finer specimens might be found. A much smaller coil, this is also MORE sensitive but the user should work slower on the same ground due to the smaller detection field. If you were visiting a known site for gold, this is a pretty handy coil. It is waterproof and can be immersed in streams to search from clumps of smaller gold, small specimens in quartz or even very small nuggets. I tested this coil on a 0.02g 'micro-nugget' and found it responded nicely if the target this small is on the surface. That's a pretty small fleck of gold too! The 5x10" Elliptical Coil could NOT detect a sample this small under any circumstance. The Emission Field is almost like a knife blade on the 6" DD. I believe the Emission Field on the 6" to be sharper in shape and far more sensitive to gold that the Elliptical although the Elliptical is capable of detecting gold that is not near the actual coil or the blade.



I'm fond of both these coils but I'm baffled as to which coil to use myself sometimes.

I like the Elliptical. It even looks good on the detector. But if it misses VERY small gold, then I wonder sometimes if it's strong enough for me to rely on it. It costs me time and money to get to the right place and I have to take into account many other things including weather. I don't want to waste time with the wrong coil. Should I use the Elliptical and then change coils if I find something? I honestly don't know ...but this is what I have done in the past. Like owning a camera with two different lenses: if you take an expensive vacation and one lens is damaged or breaks... you can still complete your trip and take pictures with the remaining lens, regardless of the zoom. Same goes for coils. In some instances, serious prospectors take two detectors with them in case of mishap. So carrying an additional coil with me may have its benefits.

In under a week, I am traveling to a location which was once VERY rich in nuggets in the mid-1800s. I just found the details last night (!) which few people know about since it wasn't considered to be as high profile as other gold fields near here. I stayed up last night till 6am marking the map that my friend will use to navigate us there. But since the area has been dug up and 'thoroughly thrashed' (as they say) by other miners and later... detectorists, I'm going to consider detecting the area with the 6" coil. This is because I believe that any gold remaining would need to be small enough to have been missed by people who got there before me. And any larger nuggets will likewise be visible to this coil as long as the Emission Field passes over them. I believe the 6" coil penetrates deeper than the Elliptical and that may be important. I might be wrong too. But Nuggets on the surface should trigger an immediate response with either coil.

Below is the Business Card-sized manual that I used to keep in my pocket to remind me which settings to start off in.
I've pretty much memorized these details but am posting them here in case others want to print them out for use. Bit of a "Startup For Dummies" which I made after i realized I was neglecting the correct process myself at the beginning. I think I wasted my first three days with the X-Terra 70 by hitting the buttons in the wrong sequence. There's a few experienced detectorists here who wouldn't have use for it but I thought it might come in handy for newbies who don't want to carry their manual around with them on their first few trips.

Cheers,

Marco



Fold Down the Middle. Laminate if desired.


Thanks Marco, just what I needed for tomorrow.
Posted by: AuzeeSheila
Date: March 09, 2008 05:19AM
I have printed out most of what is written in FAQ, but my memory is not what it used to be and I really appreciate your efforts and your willingness to share your info.
Sheila.



When someone says, ''Maybe I'm wrong but. . . ," you can be pretty sure they are right.

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Another fine post Marco.......with your permission, I'd like to....
Posted by: Digger
Date: March 09, 2008 10:08AM
add this one to the FAQFAQ section on the forum. Awesome graphics!!! Thanks. HH Randy



You'll never know for sure......unless you dig it! HH "Digger"




After more than 46-years of detecting, and having owned dozens of different detectors, I've come to the conclusion that maintaining success in the field is largely dependent on three things..... choice of site, acquiring a proper skill set for the detector and the detector itself..... in that order. Research, practice and persistence. There are no substitutes.

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Re: 5x10" DD/HF Coil and the 6" DD/HF Coil - Visible Differences
Posted by: nero_design
Date: March 09, 2008 10:38AM
You're most welcome, Digger. Go right ahead.

I spent tonight repeatedly mounting both coils to the X-Terra 70 and testing a variety of gold nuggets of various shapes and sizes (minute shapes the size of a pinhead to spherical shapes over 5 grams). It would best be described as playing with two different shaped magnets! The shape of the detection field around the two coils is very much like the above images. The coils react when any metal enters the "green halo" zone. This halo extends on both top and bottom of the coils - even if this is not apparent in the illustrations.

The Elliptical was LESS sensitive to TINY nuggets, yet the 6" was easily able to detect their presence when they were close.

With slightly larger nuggets, the 6" coil was unable to detect targets that were not in the "projected emission blade" yet the Elliptical could easily sense them as they approached the ege of the coil - above or below it... Even if they did not enter the projected emission blade area of the Elliptical coil.

But both coils are VERY similar! I found it hard to see a CLEAR benefit for one or the other at first glance. One comes with a replaceable Scuff Cover and a larger footprint.... the other is Waterproof, more sensitive to smaller targets and fits in narrow places. The Elliptical certainly has a wider Emission Blade - which has "soft" edges. The 6" had a more defined Emission Field Blade which appeared tighter, narrower and projected further than that of the Elliptical.

The ends (front and rear tip) of the Elliptical are slightly more sensitive than previously noted.

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"I found it hard to see a CLEAR benefit for one or the other at first glance."
Posted by: BarnacleBill
Date: March 09, 2008 12:20PM
In field use over a 10ft(3m) x 10ft(3m) heavily iron trash infested area will demonstrate the differences readily. Methodically covering the area first with the 5x10", then 6"HF DD, will be an eye opening experience. The 5x10" is excellent in trash, but the 6" HF DD is Nirvana.:smile:

And I define high iron infestation as a new piece of iron about every two inches or so in every direction.

HH
BarnacleBill

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Re: 5x10" DD/HF Coil and the 6" DD/HF Coil - Visible Differences
Posted by: I a thr
Date: March 09, 2008 05:27PM
Marco GOOD read...!!! :thumbup: I just got my X70 late last Fall so am very anxious to get out this Spring and do some serious detectiong. I hunt about 90% of my time with some real tough competition so the more I can learn the better my edge might be.:twodetecting: I live in an area that has very low mineralizattion so CC coils work rather well here. I have the stock 9" 7.75Khz, 6" 7.75Khz cc, 9" 3khz, and just recently traded my 6" 18.75Khz for a 5X10 Elip 18.75Khz. Reason being the two 6" coils performed very similar in my area, but still wanted a high frq coil. The elip coil I am hoping may give me better ground coverage in the many corn filed we hunt and still have that 18.75Khz for those lost gold coins. Your read gives me confidence I did the right thing for my area of the country as I don't have the opportunity to find any raw gold.
Now if the darn snow would leave us alone and the ground would thaw out Digger and I will be out there doing our thing.
PS I will probably carry a copy of your Start up for Dummies, just in case.. I wouldn't need it if I would quit alternating different machies and concentrate on just the best.
Bill

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Re: "I found it hard to see a CLEAR benefit for one or the other at first glance."
Posted by: Jackpine Savage
Date: March 09, 2008 06:46PM
Quote

And I define high iron infestation as a new piece of iron about every two inches or so in every direction

Ijzerhandelaar!!

de jackpinewilde

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Re: 5x10" DD/HF Coil and the 6" DD/HF Coil - Visible Differences
Posted by: nero_design
Date: March 09, 2008 10:56PM


I didn't connect my Concentric coil last night but from memory, the Primary Emission Field (strongest) is more like a Cone shape (Red).
The secondary (weaker) field appears to form two big disc shaped fields on top and bottom (Green).


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My graphics leave a lot to be desired. And I didn't use any.....
Posted by: Digger
Date: March 09, 2008 11:26PM
sophisticated test gear. But when I tested my concentric coils with various targets, and mapped the detection pattern based on audio response and visual TID, my results looked more like this.....




Less of a "cone shape" and more rounded at the bottom. I believe I referred to this as an "inverted half melon" when I posted this initially.

HH Randy



You'll never know for sure......unless you dig it! HH "Digger"




After more than 46-years of detecting, and having owned dozens of different detectors, I've come to the conclusion that maintaining success in the field is largely dependent on three things..... choice of site, acquiring a proper skill set for the detector and the detector itself..... in that order. Research, practice and persistence. There are no substitutes.


Re: 5x10" DD/HF Coil and the 6" DD/HF Coil - Visible Differences
Posted by: Mick in Dubbo
Date: March 10, 2008 05:39AM
Thanks guys for a couple of exellent posts.
Mick Evans.

Re: 5x10" DD/HF Coil and the 6" DD/HF Coil - Visible Differences
Posted by: SLOPSPOP
Date: May 12, 2008 12:43AM
THANKS for the great posts guys!! It will be a lot of help out in the field.
MIKE

Thanks, great work.N/T
Posted by: bfodnes
Date: May 12, 2008 04:18AM

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Re: 5x10" DD/HF Coil and the 6" DD/HF Coil - Visible DifferencesN/T
Posted by: ThirdDay_2
Date: June 03, 2008 12:38AM

(This message does not contain any text.)


Re: 5x10" DD/HF Coil and the 6" DD/HF Coil - Visible Differences
Posted by: ThirdDay_2
Date: June 03, 2008 12:58AM
I just want to say thank you for the great posts. I just ordered the X70 Yesterday morning (the Pro pack...which contains a ton of freebies, including: the standard 9" 7.5kHz and the 5X10 DD 18.75kHz as well as several hundred in add ons from KELLYCO and MineLab). I asked the salesperson what "extra" coil would make the most sense for me to buy (as someone who will relic hunt about 70% of the time and "prospect" the other 30%) and she suggested the 6"DD (18.75). Right before I came to this site I made myself a note, because I started thinking to myself...."OK Self, Why did she suggest a 5X10 and a 6 DD both with the high frequency and describe the 5X10 DD to be best suited for "clean" areas to search for gold and even jewelry or coins, but the 6"DD was suggested to be good for small/tight spots around metal items (such as ladders/pipes/bleachers/etc). The salesperson said the 9" 7.5kHz was good for general relic hunting....and while I still don't quite understand why the 5X10 and 6"DD's... with the same frequency (I'm a total newbie..only been detecting half a dozen times years ago..using a friends detector) ...are best for totally different types of terrain, I do see that Nero and Barnacle Bill (and others I may have missed the names of) seem to think that having both are wise...so I wont call back the lady and suspiciously ask why she suggested that combination.
If you (nero, bb or someone else) could clarify "WHY" the two coils with the same frequencies work best in such opposite terrain's?

Thanks in advance-
The New Guy.

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Let's talk trash.:lol:
Posted by: BarnacleBill
Date: June 03, 2008 06:19AM
Being DD coils they have a heel to toe blade pattern as in the wonderful illustration by Nero. One pattern is 10.5 inches long and the other only six. In the simple drawing below the black items are trash and could mask the good items under a different part of the 10.5 coil.



But this is not to say the 5x10 doesn't do well in trash, it does very well with more coverage than the six. But the little DD is so good that it is very difficult to take off once you've used it in heavy trash. At the moment for shore hunting I am running the 10.5 MF DD on the X70, and the 6 HF DD on the X50 so I can make a quick change over. For beach and wading the 10.5 HF DD and 6 HF DD.

HH
BarnacleBill


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