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Making A Drag Coil From Scratch


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I was working with a UXO team once (unexploded ordnance) at a test facility out here in California. They used a high brush mower first to prep their search area by clearing out the brush and then went in with a quad pulling a PVC trailer with an array of sensors, probably 10 feet wide, behind it.  The trailer had large diameter wheels so it could clear the brush stumps. I’m not sure if the sensors were magnetometers or some other metal detecting sensor, but they were each hooked up to a GPS plotting recorder. The trailer sat about 15 feet back behind the quad with a long arm and they would drive very large areas with it rather slowly. Once they were finished, their team would go in where all the hot points were plotted and would pop them still in the ground with a disruptor device or using small explosives.  That was one expensive metal detector, but it worked really nicely.

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14 hours ago, Aureous said:

ya gotta mount the thing behind a vehicle.

Hi Aureous and @Reg Wilson .   I am hearing you and trust me, if I had the option it would be definitely be mounted behind a vehicle.  Unfortunately it just isn't an option.  My wife and kids have zero interest in this hobby and therefore gold finds have to fund the next purchase and adventure and gold finds this year were slimmer than last!  When we lived in Arnhem Land and I bought a $45,000 bought that was not an issue in the slightest because everyone got use out of that  😉

So, I either give up on the idea altogether or I push ahead, try to be a bit inventive and work with what I have been provided.  For better or worse I am a stupidly optimistic bugger so will plow ahead - nothing ventured, nothing gained, right?  😁

On 5/17/2023 at 9:01 AM, Reg Wilson said:

What it did do was to eliminate large areas that could have been productive (but weren't).

Great point Reg and probably almost more of the point of making the coil.  We wasted so much time trying to extend patches on our recent trip (to no avail) where that time could have been used elsewhere if we could have gridded quicker.  

On 5/17/2023 at 9:01 AM, Reg Wilson said:

Mono coils are the go for sledding

I'm wondering if you could please expand on this Reg?  A P.A. member has contacted me privately and provided some great info but has pretty much said that AI coils are the way to go to decrease EMI and ground noise/salt signal as much as possible, and then settings can be ramped up a little.  

Now, I don't know either way but my small brain has me sitting on the fence because:

 - re: EMI.  With no tow vehicle and mostly remote W.A. locations I am hoping EMI would not affect a mono to any great degree.  

 - re: ground noise/salt signal.  I know the 17" coil on the GPX6000 struggled at times this year and last year due to salt signal whereas the 11" fared much better.   It has me thinking that a 50" mono is just going to be a nightmare in W.A.  Or are you using the myriad of settings on the older GPX's to get the mono usable?   

Cheers, N.E.  

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6 hours ago, Northeast said:

I'm wondering if you could please expand on this Reg?  A P.A. member has contacted me privately and provided some great info but has pretty much said that AI coils are the way to go to decrease EMI and ground noise/salt signal as much as possible, and then settings can be ramped up a little.  

Now, I don't know either way but my small brain has me sitting on the fence because:

 - re: EMI.  With no tow vehicle and mostly remote W.A. locations I am hoping EMI would not affect a mono to any great degree.  

 - re: ground noise/salt signal.  I know the 17" coil on the GPX6000 struggled at times this year and last year due to salt signal whereas the 11" fared much better.   It has me thinking that a 50" mono is just going to be a nightmare in W.A.  Or are you using the myriad of settings on the older GPX's to get the mono usable?

A full sized mono is always more ideal, but if you are anywhere near salt terrain, a folded mono AI coil will be a godsend....plus if a petrol vehicle is used, the EMI from that will be nullified. And yeah, if the AI is used, ya can run the gain higher or play with various timings/settings. Both of the drag coils I built were AI designs for use with quad bikes. Sensitivity was C. half a .22 bullet and depth was about 2 feet max on a 5oz lead ingot, so not the best. Reg is right....if ya can run a mono, go with that.

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I found it! The trailer I mentioned was much like this one:

IMG_1029.jpeg.9d9b64bb8b2fa7dc3824326866544d1c.jpeg

also here’s a detection cart that might be useful but not for air travel…

IMG_1030.jpeg.04f8d5f14d93cde12160681c28f3bfbb.jpeg

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The main thing with a drag coil is that it is very useful for covering a large open area that is a "virgin patch" area to see if there is gold in it. Then to find the majority of the gold you have to grid/chain the area with a normal/small coil and then a large hand held coil in the deeper ground as the depth of the smaller coil targets get deeper. Just think how many of your nuggets would of been detected with a 25+ inch coil if you did not know they were there, however very deep larger nuggets would be missed with a small coil. I would of been lucky if I used a very large coil more than 1% of the time. So the best spots to use a drag coil is in large clear non flogged/known locations, I hope this lets you know what you are getting into.

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The wheeled rig in the photo might be okay for finding cannon balls but useless for prospecting. Note how far the ATV is from the coil. That is because it is 4 stroke and would play hell with the electronics, plus the lead being so long would suffer from voltage drop.

I've tried the wheel setup but found it impractical. Too much jolting resulting in false signalling. The conveyer belt is very smooth, partly because of the weight, which makes it impractical for towing by hand. (unless you are Hercules)

One option is to build a large coil like Jim Stewart's 'Bismarck' only instead of wearing it in a bulky harness swing it like a line trimmer using a sling and counter balance it with a battery. I have seen this method used to great success in central Victoria and WA by John-Hider Smith, one of the best and most talented prospectors who ever swung a coil.

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13 hours ago, Reg Wilson said:

One option is to build a large coil like Jim Stewart's 'Bismarck' only instead of wearing it in a bulky harness swing it like a line trimmer using a sling and counter balance it with a battery. I have seen this method used to great success in central Victoria and WA by John-Hider Smith, one of the best and most talented prospectors who ever swung a coil.

The man himself-

 

 

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I have been detecting for 45 years in WA and have played around with more than a dozen drag coil configurations. I have also used a 30 x7 patch finder coil on a 4500 with great success on the type of ground you are intending to prospect. It is light, very sensitive, quiet and enables a swing coverage greater than you are aiming for. No great expense , no problems. It will achieve everything you are hoping for. 

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  • 2 weeks later...

Northeast  

 I was looking for something else and ran across another I guess you could call a deep detector.

 If nothing else it’s something to look at and wonder.

10A9126E-BBA9-435B-AEDA-7240909627E1.jpeg

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