TESORO GOLDEN SABRE

[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?

[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]

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!

[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

[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]

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]

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.

[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).

[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.

[zzy]

Hi Ivconic,Now,I null the coil at 17mv VPP,the sense is good.
but I have another question,please help me.
Just like you had said i use two separate coaxials cable. the question is
if i tuch the cable,or bend the cable,the machine will beep.it make me crazy.

Regards and thanks for your support.
Here is my coil and cable.[ATTACH][ATTACH][/ATTACH][/ATTACH]

[WM6]

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

Agre Aziz. There is new "cComega" thread on coil section. You are welcome! Others too. Suggest to publish by ivconic presented diameter related coil Em field presentation in the same thread. This tread become extensive.

[ivconic]

Hi Ivconic,Now,I null the coil at 17mv VPP,the sense is good.
but I have another question,please help me.
Just like you had said i use two separate coaxials cable. the question is
if i tuch the cable,or bend the cable,the machine will beep.it make me crazy.

Regards and thanks for your support.
Here is my coil and cable.

Shouldn't!? Try to adjust GEB trimmer a bit. RX is connected to gnd in coil but not on pcb. Both Al foils are connected togather as well as both cable shields - in coil, but separatelly at pcb, without RX on gnd (as told before).

[ivconic]

Using CRT holder for housing - nice! Really do have look and shape!

[ivconic]

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.

Due fact i dont have another way to test this, i used small em probe to locate em field arround coil. Pretty rough method, but gives me also some "picture" about em field shape and size. And i noticed pretty sharp pike look like eliptical shape arround small 20cm coil.On other hand "soft" and more look like circle shape arround 32cm coil. And size of smaller shape was almost the same as at larger coil. Size or reach of em. Yes this is not quite accurate method, but right now i dont have better method. Zahori can be adjuste at very low sense to do this job - em field probe. Only good imagination is needed to picture em shape and nothing else...

[ivconic]

Instead telescope antenna on Zahori, i put small 2cm coil taken from old 5.25" floppy (step motor in in has several coil segments - small and cute for this job)...