11” coil bs 6” coil

[pulltaboo]

So basically you have to sweep the 6” coil im 1-2” increments vs 6” increments with the 11” coil?
I would think you can sweep the 11” coil in 11” increments and 6” in 6” to cover all the ground with a DD coil

This is not specific to Nokta detectors, all coils have a "field of view" that thins out with depth. Searching at the maximum depth requires a lot of overlap.

 

[DigDog]

This is not specific to Nokta detectors, all coils have a "field of view" that thins out with depth. Searching at the maximum depth requires a lot of overlap.

So going to overlap, thats what im sayin with the 6” coil for example you are only covering 1-2” at a time at maximum depth?
If you wanted to cover just a small two foot 24” strip going forward which is nothing, you have to overlap every 2” max making a total of 12 sweeps minimum in a two foot area to cover 100% of the ground at maximum depth..
No wonder so much stuff gets missed

 

[DigDog]

This is not specific to Nokta detectors, all coils have a "field of view" that thins out with depth. Searching at the maximum depth requires a lot of overlap.

As for the detection field as I understand it on a concentric coil it is mire if a U to V shape being the deepest in the center and can see having to really overlap, but in a DD coil it’s supposed to be pretty much a rectangle shape where the detection field is the same depth from the front tip of the coil to the rear tip.
Therefore you are supposed to have even coverage front to back. If the coil is 6” and say goes 9” deep it should give you a swathe of 6” long maybe 1-2” wide and 9” deep.
Then all you should have to do is sweep every 6” back and forth overlap slightly maybe an inch to cover everything evenly.
From what I understand you are saying is you have to sweep back and forth every 1-2” to cover everything evenly on a 6” DD coil which is what I thought was the case on a concentric coil.
I could be looking at all this wrong,

 

[pulltaboo]

No wonder so much stuff gets missed

Exactly.
To help you visualize what it looks like (at the risk of explaining the internet as "series of tubes", which was a correct metaphor, by the way)… There's no such thing as a rectangular magnetic field when you're dealing with simple coils (it could be achieved with something like a phased array though). So in case of DD coils, no matter if tx/rx antennas are D or O shaped, the emitted field (or rx "field of view") will be more or less conical.
Now, to the "visualizing" part… Imagine that each of your coils in a DD arrangement have a very thin rubber membrane stretched over it. You drop a musketball in the middle of each and let the membranes stretch to their limits. Repeat for both sides. That'll be your antenna pattern. And your detection pattern will be where these two shapes overlap. Now, if you "look" at this overlap from the side, with larger coils it will be more rounded, while on "sniper" sized ones it'll be almost triangular. It's just the matter of shape, overlap and scale. You want more "rectangular" overlap? Get an elliptical.
Again, we're talking extreme detection range here, which is seldom correlates with the real world and largely depends on conductivity and inductivity of your targets. Naturally, small mid/low conductors (read "thin gold chains") are very hard to detect at maximum depth, all other things been equal. A silver dollar, on the other hand, will easily set off the machine from way outside that overlap we've just visualized.

 

[DigDog]

Exactly.
To help you visualize what it looks like (at the risk of explaining the internet as "series of tubes", which was a correct metaphor, by the way)… There's no such thing as a rectangular magnetic field when you're dealing with simple coils (it could be achieved with something like a phased array though). So in case of DD coils, no matter if tx/rx antennas are D or O shaped, the emitted field (or rx "field of view") will be more or less conical.
Now, to the "visualizing" part… Imagine that each of your coils in a DD arrangement have a very thin rubber membrane stretched over it. You drop a musketball in the middle of each and let the membranes stretch to their limits. Repeat for both sides. That'll be your antenna pattern. And your detection pattern will be where these two shapes overlap. Now, if you "look" at this overlap from the side, with larger coils it will be more rounded, while on "sniper" sized ones it'll be almost triangular. It's just the matter of shape, overlap and scale. You want more "rectangular" overlap? Get an elliptical.
Again, we're talking extreme detection range here, which is seldom correlates with the real world and largely depends on conductivity and inductivity of your targets. Naturally, small mid/low conductors (read "thin gold chains") are very hard to detect at maximum depth, all other things been equal. A silver dollar, on the other hand, will easily set off the machine from way outside that overlap we've just visualized.

So since there are rarely if any old coins here and clad is not so interesting jewelry is primarily the targets to look for .With that being said then which coil more likely to see very small jewelry?
And you saying the larger 11” DD coil will have more detection range at the bottom , not size wise per say but shape wise than a 6”?
Example a 11” dd coil looking at the side view at the bottom has a wider range maybe like a U shape where a 6” is more pointy like the tip of a V
Both not U shaped or V shaped at the bottom equally.
Again i always understood from diagrams that the dd is more [_] shaped
Looking from side and as you can see even across the bottom
And you are saying it is more U or V depending on size of DD

 

[pulltaboo]

And you are saying it is more U or V depending on size of DD

This is exactly what I'm saying. All the "diagrams" with "[_]" shapes are just marketing hoopla.
As for small jewelry, the size of your coil mostly matters in the trash. If you have no trash (for example, on some beaches), go as big as EMI would permit to increase your coverage per sweep.
The choice of frequencies is the most important part if you're after tiny gold… M1 and M3 won't see it at all in most cases. Your best bets are M2 and 40 KHz.

 

[DigDog]

This is exactly what I'm saying. All the "diagrams" with "[_]" shapes are just marketing hoopla.
As for small jewelry, the size of your coil mostly matters in the trash. If you have no trash (for example, on some beaches), go as big as EMI would permit to increase your coverage per sweep.
The choice of frequencies is the most important part if you're after tiny gold… M1 and M3 won't see it at all in most cases. Your best bets are M2 and 40 KHz.

Wonder the difference really between park mode m1 and park m2
Park m2 probably uses two higher frequencies than park m1 I suppose.
I would think using m2 two frequencies better chances on small gold jewelry than single frequency 20 or 40. The biggest difference being probably depth

 

[pulltaboo]

Wonder the difference really between park mode m1 and park m2

IMO, M1 is weighted towards middle of the frequency spectrum, M2 – higher end, and M3 – lower end of the spectrum.
Both M2 and 40 KHz have a ridiculous resolution, they will easily detect pieces so tiny that your pinpointer won't be able to locate them (and you'll need a loupe).

 

[DigDog]

IMO, M1 is weighted towards middle of the frequency spectrum, M2 – higher end, and M3 – lower end of the spectrum.
Both M2 and 40 KHz have a ridiculous resolution, they will easily detect pieces so tiny that your pinpointer won't be able to locate them (and you'll need a loupe).

I would bet 20 KHz probably does pretty good as well unless your prospecting

 

[pulltaboo]

I would bet 20 KHz probably does pretty good as well unless your prospecting

Depends on how small you want to go. For thin gold chains at the beach I'd prefer 40 KHz, unless there's a strong EMI on this frequency. Tiny gold jewelry on tot lots and event fields? M2, as it gives you the benefit of IF adjustments.

 

[DigDog]

Depends on how small you want to go. For thin gold chains at the beach I'd prefer 40 KHz, unless there's a strong EMI on this frequency. Tiny gold jewelry on tot lots and event fields? M2, as it gives you the benefit of IF adjustments.

Isn’t there a correlation between frequencies and depth as well?
Lower frequencies go deeper as I understand especially in mineralized soil.
I think you are in Ga, lots of clay and mineralization. Here in Fl we don’t have dirt lol. We have basically loose sandy soil. Lots of sugar sand very little to no mineralization on dry land which is a plus but the big down side hard to find any old targets for one lack of areas with history, old coins and relics are extremely rare, and the sink rate is higher because of the loose sandy soil.
Even vegetation is hard to grow here nutrients and water just don’t hold in the sand

 

[pulltaboo]

Isn’t there a correlation between frequencies and depth as well?
Lower frequencies go deeper as I understand especially in mineralized soil.
I think you are in Ga, lots of clay and mineralization. Here in Fl we don’t have dirt lol. We have basically loose sandy soil. Lots of sugar sand very little to no mineralization on dry land which is a plus but the big down side hard to find any old targets for one lack of areas with history, old coins and relics are extremely rare, and the sink rate is higher because of the loose sandy soil.
Even vegetation is hard to grow here nutrients and water just don’t hold in the sand

Yes, lower frequencies usually go deeper, but higher frequencies see smaller objects. Latter is not always a good thing… For example, on many virgin tot lots there's so much tiny bits of foil that you won't be able to find anything meaningful unless you switch to lower frequency (which will be pretty much foil blind) or pick every single bit of that stuff. With limited time, lower frequency at the expense of small gold is an obvious choice.