TESORO GOLDEN SABRE

[WM6]

What i want to see from your software is; if there is differences in em field shapes at smaller and larger coils. How can i explain this!?
I could swear smaller diamm. coils do have "sharper" and stronger elipse (like on picture) than larger diamm. coils.
Depth rise is not proportional to diamm. rise, for sure!
It falls respectivelly diamm. rise.
If you unedrstood me ....bravo! If not...i dont blame you at all!

Yes, ivconic it would be interesting to present field shapes of different coil diameter alone. At the same time we can not forget that construction of overlapping coils (DD, OO, Omega) considerable reduce Q of both coils. Catch is to find not so overlapping coil, but still capable to tunning/nulling and RX diameter as big as possible. Maybe OO disturb Q of both coil least of all in account of unpractical shape.

[WM6]

Yes of course. But it will take some days.

The reason for good performance on small cc-coils is the following:

a) Magnetic field strength distribution on small coils are higher compared to bigger coils. So targets induce signals proportional to the magnetic field strength.

b) Your target is not changing. The caused inductive effects remain almost same compared to the bigger coils (in case of same magnetic field strength distribution). But on the bigger coils you will also have bigger RX-coil, the effects have to cover bigger flux area of the RX coil to be detected. The relation of the target size (thus effects) and the flux area of the rx-coil (covered sensing area) is relevant. Therefore small coils increase the signal-to-noise ratio due to the relation factor

c) combination of a) and b) affecting the total result.

Aziz

Bingo Aziz. Fully agree: better results in deep of bigger coil are primarily on (usually) bigger RX coil part. Because of this I put on start this CC and Omega section a question about exchange TX and RX coil position, so RX coil on outer position are bigger and according this we can expect better results in deep and worse in pinpointing (challenge to constructor to combine both). DD and OO coil (Nexus chose) are good answer on this, but maybe not a single. Here a big attention have to be paid on Q of both coil too (Q as handy replacement of stronger TX oscillator).

[Fred]

did anyone tried to change the osciallator of the circuit (TGS..) and replaced by another one?

Hi Aziz,
I didn´t,but i think Ivconic mentioned some experiments with this.
But such a hight power wouldn´t be a problem for the RX stage, making a reasonable nulling impossible and saturating the preamp?
Could be OK for a 2-box maybe?
Regards,
Fred.

[Aziz]

Aziz, what about "Comega" coils for a name ?

Regards,
Fred.

Sounds good. We should wait for WM6 's proposal. It was his idea.



By the way,

did anyone tried to change the osciallator of the circuit (TGS..) and replaced by another one? I remember, six years ago or so, I built a very simple high-power oscillator, that was able to induce very high magnetic fields. This oscillator was even able to heat the low resistant coil and induced peak voltage above >100 V on pure sine waves on the coil!!!
This oscillator was incredible powerfull. It was even able to induce the low frequency (~10 - 11 kHz) into my ears at a distance of 1-2 m!!! (really not joke!).

I have'nt the schematic anymore. But I have some pcb boards, that have to be reverse engineered. I know the most of the LC oscillators on metal detectors work on very low power mode.
This could increase the signal-to-noise-ratio dramatically. Even, when the oscillator is not used at 10-30 W power dissipation. It would be enough to limit the power to 0.5 - 2 W.

Anyone tried this yet?

[Fred]

Hi Ivconic,
Thanks for infos.As i said before i used my TGS with a omega coil made for the Magnum, and it worked very well.With my DD coil i could achieve more depth, but not as easy to work with.
I think size between 22 and 25cm would be great.
It is also easier to find forms, and CRT monitors supports are great for this purpose:very rigid,looking good , and with separations for the coils that you can fill with resin .Old monitors are easier to find by now .

Aziz, what about "Comega" coils for a name ?

Regards,
Fred.

[Aziz]

What i want to see from your software is; if there is differences in em field shapes at smaller and larger coils. How can i explain this!?
I could swear smaller diamm. coils do have "sharper" and stronger elipse (like on picture) than larger diamm. coils.
Depth rise is not proportional to diamm. rise, for sure!
It falls respectivelly diamm. rise.
If you unedrstood me ....bravo! If not...i dont blame you at all!

Yes of course. But it will take some days.

The reason for good performance on small cc-coils is the following:

a) Magnetic field strength distribution on small coils are higher compared to bigger coils. So targets induce signals proportional to the magnetic field strength.

b) Your target is not changing. The caused inductive effects remain almost same compared to the bigger coils (in case of same magnetic field strength distribution). But on the bigger coils you will also have bigger rx-coil, the effects have to cover bigger flux area of the rx coil to be detected. The relation of the target size (thus effects) and the flux area of the rx-coil (covered sensing area) is relevant. Therefore small coils increase the signal-to-noise ratio due to the relation factor.

c) combination of a) and b) affecting the total result.

Aziz

[ivconic]

What i want to see from your software is; if there is differences in em field shapes at smaller and larger coils. How can i explain this!?
I could swear smaller diamm. coils do have "sharper" and stronger elipse (like on picture) than larger diamm. coils.
Depth rise is not proportional to diamm. rise, for sure!
It falls respectivelly diamm. rise.
If you unedrstood me ....bravo! If not...i dont blame you at all!

[ivconic]

"...let's say 10cm c.c. coila and 27 cm ..."
Sorry mistake here!!
should say:

"...let's say 18cm c.c. coil and 27cm..."

[ivconic]

One more thing; recently i made Eldorado. It works by the book. But i had not so good results with it using already made DD coils for TGSL. Average.
I was thinking to make another DD for Eldorado. Now, i dont think so.
I think omega coil will be more suitable for it.

Recently also (few days ago) i got Fisher 1265. In very good shape. It came with small 20cm C.C. coil. Certainly can not beat TGSL in depth, yet it is very powerfull, keeping in mind such small coil. I went outdoor with it and was amazed how great "collector" it turned to be...!
So again, i think we must reconsider smaller diammeter coils here. I dont think larger diammeter coils are superior in depths over small diammeter coils.
Aziz, i think your software could be used to see real differences between .... let's say 10cm c.c. coila and 27 cm c.c. coil.
I could swear that depth rise is not analogue respecting diammeter rise.
I think it falls with every cm added in diammeter.
Can you simulate several c.c. coils, starting from 18cm in diammeter up to 32cm...?
And post those here or any other thread on this forum?

[Aziz]

...Huh, it will need further calculations and experiments to find exact number of turns for coils.

Just call me! And you will save time and money!

This is a good job for my coil software.

[ivconic]

Hi Ivconic,
nice to hear you are on the way with new coil for TGS! This time omega one ! Cool!

Why so small ? Just a trial ? 21cm round is good for e.g. trashy sites and with extremely precision pinpointing... but I think it cannot compete with your older large DD on depth sector.

I think a good one will be in the 10'' range... so about 25cm external round TX. This could match DD performances and also give better than before , with lose of widescan but much better pinpointing.

What do you think ?

Kind regards,
Max

Yes, it started as trial coil and turned to very serious ideas to adopt this as main type of coil for TGSL....
I didnt expected such good results at all!?
Most important fact is that this omega coil is indeed stabile as a rock.
I will repeat, it is very hard to balance it. Much harder than usuall dd coils.
But once it is nulled, well...well...
It think it will beat DD coil in depth also.
Not to mention narrowed area of detection.Pinpointing is 100% accurate with it. Actually area of detection is exact area covered by RX coil, no more, no less. In the past i made 2-3 omega coils for that md 3007, which was nomotion metal detector, poor performances comparing to TGSL. I didnt payed much of attention on those omega coils at the time. Those were made just to test detector, since original coil came with it was omega coil. I made few copies of md 3007 and logically made also coils for those by copying original coil. So i burried in my mind those as not so serious coils.
Now, i am equiped with more experience and payed a lot of attention on balancing and remaining exact inductances needed by TGSL.
I think i will propbably switch to this kind of coils in future. Yes next would be larger omega coil, at least 25-27cm. Huh, it will need further calculations and experiments to find exact number of turns for coils.
This time 0.25mm wire is used. On larger coil i guess 0.3mm would be more suitable to be used.
We will see...

[Aziz]

WM6,

Thanks, I missed the graph to check the model. By the way, the computer model is done. I found that the proposal coil design above can not be nulled. The inner TX coil has to be on opposite direction to the outer TX coil. It does not matter. I will explain on some impressive graphics why this model does not work. But it will work on opposite current direction. Also the one third winding factor will very likely not enough to get nulled.

May be I should post the comprehensive results on the coil section to not disturbing the other contributors here. Please make a starting thread and I will post every step consequently. So at the and, we can make a prototype of nulled "Omega-concentric" coil. (How should we name this type of coil?)

Aziz

[WM6]

Hi Aziz, I think we are close to basic idea.
Must be very artistic to simulate this.
Maybe only this addition about balancing/tunning:

Aziz missing sketch:

[WM6]

OK
What to say more? Need to finish it and than perform full test outdoor on the
real field.
Until than...

Congratulation ivconic. Now still field test, wider coil and then mass production. Good job, really!

[ivconic]

OK, i got first,preliminary results;
first i have to say, nulling omega coil turned to be much
more difficult than DD coil???!
(Last time i made omega coil was for MD3007 and i didnt used
present method by measuring induced voltage in RX coil)
It need 1/10mm to drop to 0 volts or to jump to 20-30mV!!!??
After much effort somehow i managed to achieve excellent null.
At 200mV range it says 0.01...more than good!
OK, than i resoldered RX wires from miliviltmeter to TGSL.
WOW! What a stabillity!!! I dont beleive my eyes!!!
It is very,very stabile coil!!!! Superb over DD coil!!!
Discrimination is P E R F E C T !!! Perfec,perfect!!!!
Ferrite rod is absolutelly invisible for this coil even if i
lower GEB trimer much "down" from usuall value, usually trimmed
with DD coil.... Usually, when DD coil nulled well, there are some
mum "cracks" on ferrite rod with trimmer on 60%. I usually left that
way and later turns detector acts pretty well on soil.
But now, with this coil - not "cracks" at all! Trimmer at half - no
"cracks". Thin silver coin - yes, detected loud and clear!
Wow.
Ok, depth is lower than 27cm coil. 1 Euro coin detects very easy at 24cm
in air. 1.5cm nickel coin at 28cm.
Considering diammeter of this omega coil - 21cm, i think it is not
shallow comparing 27cm DD coil, not at all.
Next thing i'll do is to make 27cm Omega coil and than see real differences.
Bit now, i left out of wire, so this will wait for week or more.
But discrimination is really perfect. Large iron claws - absolutelly invisible
in disc mode.
What to say more? Need to finish it and than perform full test outdoor on the
real field.
Until than...


Regards Max!