Coil Choices For Maximum Depth

[phrunt]

Thanks JP, I was merely asking questions based upon observations, I made it very clear I don't know as I don't find big gold so yes, of course my observations are not founded on experience being in NZ ergo you already knew that.  I'm sure you're not doing a roaring trade on 19" coils from your store even though in your area the potential is there to find bigger gold as your photos demonstrate.

The 19's are very cheap on the second-hand market, probably as you pointed out above not many are willing to swing them with the weight and people chasing bigger gold that buy X-coils tend to buy the Concentrics, again likely the lighter weight is a big plus along with better smaller gold sensitivity.

We will have to see if they make a new GPZ which path they take when it comes to weights and coils.

I thought I'd ask X-coils their opinion on it, they're confident the large Concentric coils are deeper on both larger and smaller gold than a DOD coil, and they make both types obviously and one of them knows a whole lot more about physics than we do with that being his specialty, with Concentrics he said the depth is determined not by the size of the receive winding but by that of the transmit winding.  They also certainly have a lot of experience finding large deep gold.  I know nothing about this stuff so If you want to discuss the physics of it further, you're welcome to contact them, you know how.

[Aureous]

This is getting way off topic now....and a bit spicy and unnecessary.  But what I will add is that yes, it is well known that Concentric coils can be affected more by ground mineralization and the DOD design DOES offer the detectors electronics to subtract the ground signal far better. So, its a matter of using the right coil for the right soils. However, I have seen CC coils (protos) that have a unique receive coil isolator that is shielded differently to the transmit coil. This allows the receive coil to be both larger and closer to the transmit. If this was developed further, I wonder if the difference between the CC and DOD would be swapped..... EDIT....(yes an edit!). I wonder if anyone has tried to make a PI version of the Coplanar coil design? Where the transmit and receive coils are potted at a different height within the shell, old school Garrett style?... hmmmmm

[GB_Amateur]

34 minutes ago, Aureous said:

I wonder if anyone has tried to make a PI version of the Coplanar coil design? Where the transmit and receive coils are potted at a different height within the shell, old school Garrett style?... hmmmmm  (emphasis mine)

I think you are referring to what is more commonly called 'coaxial'.  As Carl points out in his new book, the terms 'coplanar', 'coaxial', and 'concentric' can be confusing because these terms literally are valid for more than one coil geometry.

[Jonathan Porter]

10 hours ago, Aureous said:

However, I have seen CC coils (protos) that have a unique receive coil isolator that is shielded differently to the transmit coil. This allows the receive coil to be both larger and closer to the transmit.

I’ve used properly designed Concentric coils back in the day during early field testing and the DOD design won out overall (yes well before X coils even existed). However the X coil variant is not wound like that with only a tiny little receive. The clear advantage of doing it that way is less EMI, sharper mono-like target response on generally smaller within range gold, and the BIG ONE, a reduction in Conductive signals due to the smaller receive. But it is a ZVT it’s attached to after all and that tech has a LOT of grunt on deep gold.

Conductive signals are a killer for the big DOD coils due to the bigger receive area, especially in places like Vic that have a LOT of clays, that and the sheer weight of the thing. I only spool up with my 19 inch when conditions are drought like. Big deep targets are broad, so are conductive signals, so big nuggets get blended in with ground noise. It’s VERY hard to carefully control a large heavy coil to avoid micro lifts and pivoting to avoid excess noise. Listening through all the threshold variation is extremely tiring, no different to the 24” Coiltek DD coil days on 2200’s etc. 

JP

[Jonathan Porter]

23 hours ago, phrunt said:

I thought I'd ask X-coils their opinion on it, they're confident the large Concentric coils are deeper on both larger and smaller gold than a DOD coil, and they make both types obviously and one of them knows a whole lot more about physics than we do with that being his specialty, with Concentrics he said the depth is determined not by the size of the receive winding but by that of the transmit winding.

After I finished laughing, honestly I couldn’t help myself, I wiped my eyes and passed it forward and gave others a good belly laugh too!! 😂 Laughter is the best medicine apparently ☺️ 

[Aureous]

Unless the Russki's have some 'secret sauce' idea about increasing transmit power (via the coil alone) to an insane degree, @phrunt, I think perhaps they misspoke. Receive ability is the primary source of signal to your ears. Which is why I mentioned the prototype CC coil I saw with an isolated, bigger receive winding, closer to the transmit one. Without a big receive, the actual depth achieved in minimized. What the benefits ARE with CC's, is the minimizing of ground signal, which masks actual targets. So, a smaller receive winding will provide better depth where ground noise is an issue.

[Aureous]

2 hours ago, GB_Amateur said:

I think you are referring to what is more commonly called 'coaxial'.  As Carl points out in his new book, the terms 'coplanar', 'coaxial', and 'concentric' can be confusing because these terms literally are valid for more than one coil geometry.

I do suspect you're right. I pulled apart an early Garrett IB coil which I thought was a co-planar. But, co-axial sounds more correct....none of the original labels were left intact. But it was a thick small coil and co-ax makes more sense now you mention it <scratching chin>

[phrunt]

8 minutes ago, Aureous said:

Unless the Russki's have some 'secret sauce' idea about increasing transmit power (via the coil alone) to an insane degree, @phrunt, I think perhaps they misspoke. Receive ability is the primary source of signal to your ears. Which is why I mentioned the prototype CC coil I saw with an isolated, bigger receive winding, closer to the transmit one. Without a big receive, the actual depth achieved in minimized. 

Possibly, quite a lot is often lost in translation 🙂

It would be interesting to put my 20" CC up against my 19" ML DOD on a deep target and see which wins, problem is digging the deep hole! Not something I'd enjoy, maybe a soil drop off ledge or something with side access holes.  Might be some fun for a day with nothing to do.  I'll make it a mission and get a video at some point when I find the right spot, I have an idea where I think I can sort it out.

[Knomad]

1 hour ago, phrunt said:

Possibly, quite a lot is often lost in translation 🙂

It would be interesting to put my 20" CC up against my 19" ML DOD on a deep target and see which wins, problem is digging the deep hole! Not something I'd enjoy, maybe a soil drop off ledge or something with side access holes.  Might be some fun for a day with nothing to do.  I'll make it a mission and get a video at some point when I find the right spot, I have an idea where I think I can sort it out.

Now that's the kind of good depth testing I remember, a sharp vertical ledge with holes bored into the side at various depths from the top, and PVC pipe put in each hole, so different targets can be inserted into the pipes, that way the ground to surface is Undisturbed, and give more accurate closer to real life results.