9" versus 11" coil with the fast program

[paleomaxx]

I've been toying with the idea of adding another coil to my arsenal with a couple of sites in mind, but wanted to see if anyone has tried something similar and how it went. Currently I have the stock 9" coil, not the x35, and my concern is depth. These are my two oldest sites and I've hammered each in all directions with great finds coming from the 3-6+" layer. I vacuumed up the large iron so there isn't much in the way of trash signals or masking, but the ground in this area is pretty rocky and mineralized so I have the best luck with the fast program.

Lately I've gotten particularly good at listening for the very faint tones that don't even register with a VDI, but you can still hear a repeatable non-ferrous tone if you go slow enough. I've found that if I take those and dig a wide plug right over them and then flip it over, it'll either be a really tiny target in the bottom of the plug, or a nice large tone deeper in the hole. Just yesterday I pulled a beautiful 1746 KGII half penny out with this technique, but despite being a pretty large piece of copper it barely registered before the plug was flipped. The other site has 4" of fill and then a 1" layer of clay with all of the older targets in the soil below those. Found a half penny in that layer recently and again I suspect there's more just a few inches below the detectable range.

What I'm hoping is that if I switch to an 11" (or even 13" coil) with all other things being equal and using the same program, I would get the same target separation with greater depth. Or does the larger signal area and greater associated noise negate any benefit? I know I can switch to the deep program with my current coil and I've worked with that as well, but I'm curious if the larger coil will add just that little extra 1-2" of depth to the same fast program performance. What do you guys think?

 

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[vferrari]

It will add perhaps an inch of depth over the 9", but the main advantage is coverage. More targets under the larger coil may introduce some issues in high target density situations affecting tiny targets, but separation on a DD coil is determined by detector recovery speed (Deus reactivity setting) not the coil so it should not be adversely affected by going to the 11". The x35 coils can be run at lower coil frequencies (<4khz) and higher transmit powers than the legacy lf coils, so that also translates to added depth for high conductors. Bottom line, the 11" x35 will probably help, but don't expect miracles. I personslly advise avoiding the 13" coil as it is actually s 13x11 elliptical which means it will not give you a noticeable depth advantage over the 11" round. It will give more swing coverage but at the expense of making the Deus nose heavy. HTH.

 

[GeoW]

At what depth was that Half Penny?

 

[paleomaxx]

It will add perhaps an inch of depth over the 9", but the main advantage is coverage. More targets under the larger coil may introduce some issues in high target density situations affecting tiny targets, but separation on a DD coil is determined by detector recovery speed (Deus reactivity setting) not the coil so it should not be adversely affected by going to the 11". The x35 coils can be run at lower coil frequencies (<4khz) and higher transmit powers than the legacy lf coils, so that also translates to added depth for high conductors. Bottom line, the 11" x35 will probably help, but don't expect miracles. I personslly advise avoiding the 13" coil as it is actually s 13x11 elliptical which means it will not give you a noticeable depth advantage over the 11" round. It will give more swing coverage but at the expense of making the Deus nose heavy. HTH.

That's very good to know. Definitely not leaning towards the 13" coil since coverage is rarely an issue. Even 1" more of depth I think will ferret out more good targets at these spots and considering what I've found to date the cost of the coil may be worth it just for the peace of mind that I'm not missing anything else.

At what depth was that Half Penny?

7" or so standing vertical. I would get a very short high tone with no VDI in one direction and a high 70's VDI in the other but not consistent numbers. Earlier this spring I learned to trust any non-ferrous tones that the fast program gave me and dig after them. I was expecting a button though; it's a regal halfpenny too so full weight of copper which should have rung higher even at depth.

 

[vferrari]

The orientation is what affected the signal strength and ID. On edge gives a smaller metallic profile from the perspective of the coil, in other words a small target. 7" on edge is a great save. Don't expect the 11" to outperform the 9" much, if at all, in that specific situation and in thick target density (junk and otherwise), I might give the edge to the 9". I think getting an 11" x35 coil to add to your arsenal is still a good idea because it expands your operating frequency range (25 khz is killer on mid conductive relics like buttons in thick iron), but like I said, don't expect miracles.

 

[Ghost-uk]

Firstly, the 13” coil is so unbalanced it’s embarrasing for xp, even with a balance block it’s shape with the added weight of its size is still terrible , I ran one alongside the 11” , next to no difference in penetration , only upside for me I think might be ground coverage .
And is that really such a good thing ? I don’t think so...I’d rather be tight with my swing and not miss anything with my 11” rather than taking more time trying to get the 13” to swing correctly and not fully concentrating on what’s going in your ears .

Don’t be obsessed with depth, 99% of things lost will be in the top 6 inches, spend more time thinking about recovery speed and accurate target identification, I can tell you how to go deep, but the machine is purely quessing at any metal target, it will give a good signal on rubbish and a poor signal on desired or vice versa, a lot of the time it will be the deeper iron giving you a great audio response ..

 

[paleomaxx]

Don’t be obsessed with depth, 99% of things lost will be in the top 6 inches, spend more time thinking about recovery speed and accurate target identification, I can tell you how to go deep, but the machine is purely quessing at any metal target, it will give a good signal on rubbish and a poor signal on desired or vice versa, a lot of the time it will be the deeper iron giving you a great audio response ..

In most cases I would agree with you; barring any plowing or other earth moving things just don't sink down that far, but both of these sites have been messed with. The yard definitely has a layer of clay and then fill so I'm fighting against that and the other site has a huge 1830's barn next to it and I suspect that some of the earth they moved to build it was spread out over the older structure's site. Even if the depth doesn't end up panning out I do like the added benefit of the 25kHz frequency with the x35 11"; I have some other spots that I'd like to try that out on. Looks like I'll be doing some shopping.