Cylinder Coils?

[Carl-NC]

DD coils give a good sweep area, but less depth, a typical tradeoff.
The concentric coils give a reduced sweep area. The concentric, induction balanced coil give less depth and less sweep area.

DD isn't as great on sweep area as manufacturers would have you believe. Here is an illustration from one manufacturer:


Here are measured results, comparing a White's 950 CC with a Fisher DD:


Only for very shallow targets does that DD (black curves) give the alleged "windshield wiper" pattern. As you go deeper, they converge to about the same coverage.

An option outside the box, would be a concentric coil where the RX coil is about the same diameter than the TX coil. I don't know if anybody has done it yet, but believe it is possible. This could be an interesting project.

Garrett SeaHunter Mk2 and Infinium both had mono-looking coils that were actually split coils (separate TX & RX coils). I assume the GPX6000 does too, otherwise their TX scheme wouldn't work.
If you mean an IB coil where TX & RX are the same size, Alexander Bell used this method in 1881:


There is the "search coil" to the right, and a counter-balance transformer to the left. In this illustration, the coils are not equal in size but they could be.

[Tinkerer]

What you mean under "tandem coil" - OO coil or some different?

More like 2 TX coils side by side, like OO, and a RX coil in the center, overlapping the TX coils for induction balance.
GPX 7000 uses something similar, but it is 2RX coils and one TX coil in the center.

The Current in the tandem TX coils can be both clockwise or one clockwise and the other counter clockwise. The magnetic fields f the 2 TX coils can be aiding or opposing.

[Detectorist#1]

What you mean under "tandem coil" - OO coil or some different?

[Tinkerer]

Yes, that is one example. The Garrett Axiom uses a CCPI pulse, plus an exponential pulse.



I don't, but it's the same thing Minelab has always said about their PI iron discrimination.

DD coils give a good sweep area, but less depth, a typical tradeoff.
The concentric coils give a reduced sweep area. The concentric, induction balanced coil give less depth and less sweep area.
An option outside the box, would be a concentric coil where the RX coil is about the same diameter than the TX coil. I don't know if anybody has done it yet, but believe it is possible. This could be an interesting project.
For different ergonomics, a tandem coil could be considered.

[Carl-NC]

Carl refers to as "constant current PI," is it the ZVT of the GPZ7000?

Yes, that is one example. The Garrett Axiom uses a CCPI pulse, plus an exponential pulse.

I am using a DD coil at present. It gives FE discrimination close to the coil, but the discrimination does not go the full depth.
Does anybody have more information about the relative depth of the FE discrimination of a DD coil?

I don't, but it's the same thing Minelab has always said about their PI iron discrimination.

[Carl-NC]

PI FE discrimination is a joke, placing the same object horizontally and vertically results in two different outcomes, small iron blocks are identified as non-iron

Same with VLF.

[hykj888]

PI FE discrimination is a joke, placing the same object horizontally and vertically results in two different outcomes, small iron blocks are identified as non-iron

[Tinkerer]

For me, CCPI means "constant current PI," so it's a variant of CCPI. It's constant current in that the pulse is not a rising exponential, but rather a constant current over the pulse interval. This is the first kind of CCPI I built back at White's, and it can use a mono coil.

There is nothing better than a mono coil for depth.
I am using a DD coil at present. It gives FE discrimination close to the coil, but the discrimination does not go the full depth.
Does anybody have more information about the relative depth of the FE discrimination of a DD coil?

[hykj888]

I have tested this coil; I used flat cable, which is intended to be used with the DP3SP. This is because the output of a large coil made with regular cable does not match the waveform required by the DP3SP system. Using this coil allows for perfect operation. Compared to traditional, it has lower parasitic capacitance. I have also tested the bipolar single coil; it is not suitable for detecting large, deep targets with a large coil because eddy current duration is very short. It is best used in a gold detector, as it can quickly sample and has high sensitivity to small gold nuggets. Carl refers to as "constant current PI," is it the ZVT of the GPZ7000? I have tested this circuit using analog circuits, it can achieve the function, but it is not perfect. It requires the support of an FPGA
Translated by 360AI。

[Carl-NC]

For me, CCPI means "constant current PI," so it's a variant of CCPI. It's constant current in that the pulse is not a rising exponential, but rather a constant current over the pulse interval. This is the first kind of CCPI I built back at White's, and it can use a mono coil.

[Tinkerer]

.... coils are coils are far as I am concerned ...without a magnetic monopole it gets hard to move outside the physics constraints.
However there are still things that can be done in the electronics. I have evolved the CCPI circuit i orginally published and now get these results.
I can punch 6 amps bipolar pulsing through a 300 uH coil or for example a 3 millihenry coil with the same fall times and no excessive flybacks.

I am still working on it so dont ask me to tell you how its done yet .. the blue trace is a 300 uh coil ... the green trace is a 3 millihenry coil.
The current pulses now fall to zero before the next pulse. 50 microseconds pulse on then off.

This is not CCPI, Continuous Current TX anymore. You have a long period with 0 current.
It is a bipolar pulsed PI. Also very interesting. It appears to be even better than the CCPI.

[Smirnov-Arta]

....

Unfortunately, you still don't understand what I wrote to you about. The ideal coil for ANY MD is 1 turn. Can you implement this in relation to your MD? If YES, then that's great! If not, then you will always have a compromise between the ideal theory and the actual MD scheme.

[Nova]

MdToday, fair enough, just one more question about 'Forties" road, yeah i do have the yearly pass, but we can't use that now, is Forties road always closed by gate?, i think when i drive past it ,it's always open, but i'm not sure, and since we aren't allowed to drive inside now, how or by what road would you choose to get into that area, thanx mate?

[Mdtoday]

MdToday, yeah mate , i have done my historical research, "Trove' brings up most of the info on his field, and yes the fork area produced the majority of the chunky nuggets from 2oz to upto 22oz that the founder of the gully was named after, there is very little mention of the other gullies except for one mention of nuggets upto 2grams found in some of them, so we know that if they were digging 2 gram nuggets at the bottom of the gully at 3 to 5ft deep then what chance do we have?, BUT people like Nenad who got in first cleaned up the known/found patches so that leaves the rest of us little to no chance of scoring any, but i might take your advice and hit those areas you mentioned as i haven't detected up that way yet, what i would like to see is a map and all the patches that have been found marked (by all the finders), since the place has been smashed it shouldn't be considered blasphemous to ask this, it's not like some new tech will come along and suddenly allow you to hit the area again and start digging up ounce chunks ( what do you think of this suggestion, still a bit too much to ask?)

Nova, If you get into the areas I noted, you will find some yellow stuff. I use a small 7 inch elliptical coil which suits the area.
Less noise, sensitive to the small stuff, still gets to the shallow bedrock or wash in the places I seek out and easy to get in and under the hakea and other brush.
On your asking suggestion, I wouldn’t but that’s just me, however I do see your point mate.

[moodz]

.... coils are coils are far as I am concerned ...without a magnetic monopole it gets hard to move outside the physics constraints.
However there are still things that can be done in the electronics. I have evolved the CCPI circuit i orginally published and now get these results.
I can punch 6 amps bipolar pulsing through a 300 uH coil or for example a 3 millihenry coil with the same fall times and no excessive flybacks.

I am still working on it so dont ask me to tell you how its done yet .. the blue trace is a 300 uh coil ... the green trace is a 3 millihenry coil.
The current pulses now fall to zero before the next pulse. 50 microseconds pulse on then off.