GPZ homebrew coil

[Kev]

Yes 6666 I imagine those beads are made of "the right stuff", if only they were 10 times larger.

I thought I'd try to find out what material Minelab used for the "yellow doughnut" since this material provides the ground balance ferrite calibration point it might also be good stuff to use as a solder/component mask, so long as it does work in stealth mode.

I found a good freeware app to use. You just wind a dozen or so tight turns on your toroid, measure and input the inductance along with dimensions and the program calculates the permeability ui and AL figures and from there you can identify the likely ferrite material.
If only they would put their makers mark on these cores, then you could rely on colour codes.

I just need to find my doughnut now, it's AWOL at the moment?

Here's a link to the program. I will also be using it to identify some of the toroids in my junk box.

Mini Ring Core Calculator
https://www.softpedia.com/get/Scienc...lculator.shtml

[Altra]

Kev, good video for identifying ferrite material.

https://www.youtube.com/watch?time_c...ature=emb_logo


Another interesting one

https://www.youtube.com/watch?v=81C4IfONt3o

[Kev]

Thanks Altra for the links, becoming much clearer now!

[6666]

Thanks Altra, at about 9:22 in the second video explains why I put the Ferrite Cores on 740's

Yes 6666 I imagine those beads are made of "the right stuff", if only they were 10 times larger.

They are made from the dull grayish colour material not the shiny black

[6666]

With 10 turns .4mm around the yellow ferrite ring which I identified the old way through colours at 10kHZ is about 1.66 uH. (DE-5000 LCR meter)

The ring I bought hoping it matched minelabs, was only matched by colour and tables, would be interesting to compare with another that has been supplied by minelab if anybody has a real one,
and yes that's how we spell colour in Australia.

The calc thats linked in the video gives my yellow ring an Initial Permeability of 13
so closest is type 15 material NiZn

[Kev]

Thanks 6666, I'll try and locate mine tonight, and run the test, it's probably rolling around the floor of the truck from my last outing, I sure hope it's not left out there on a hillside in the snow somewhere. It always crosses my mind when I toss it down on the ground, "I must remember to pick it up again" I hope i did so!

[Kev]

Hi 6666 your material might be good enough.
If I tight wind I get 10uH for 22 turns and loose wind gives 5.3uH which equates with an ui of 17.7 to 8.8 respectively.
The closest in the Amidon range is T130-6 (6 material nominal ui= 8 which matches the colour scheme also (yellow/clear)

Using another LCR meter that I don't trust as much, puts it in the T130-3 (3 material nominal ui= 35) colour plain grey.

A few makers use the yellow/clear for the type 6 mix, so we might be close enough to assume that this is the ground susceptibility benchmark Minelab use.

I've been thinking about the coil embedded ferrites as a persistent calibration factor, and now dismiss it, since it is always static in relation to the two coils. The key to getting a quick GB on the 7000 is to pass over the toroid in a few directions as quickly as possible after depressing the GB switch. It may have the added advantage of providing RX/TX/RX coil balance information, I'm not sure.

But, a number of sources are raving about the performance of 10x9 X-coil, and I just wonder if they have used these large ferrite clip-ons in that coil as well?
Could it be that these are focusing part of the field and intensifying central density? Where's Aziz these days?

[6666]

Thanks, I tried with 22 turns, as tight as I could get the turns and even spread varied about 5.7 uH, the spread made a difference but averaged ~ 5.7uH
it seems the biggest claim with the x coils is some how they run a bit quieter, so you can turn the gain up

[6666]

I just realized that when you said tight you meant close wind, so I squeezed my windings close together as possible and got ~9.7 uH, so pretty close

[Kev]

6666 Is your toroid yellow?
I see that Amidon Iron Powder type 15 is red and has an ui of 25.
Seems the make introduces much latitude, but a few 10s of ui here or there shouldn't matter when they can be in the order of many thousands.
26 turns on a green one I have here measure 3.6mH with a ui 0f 6600, clearly that one wouldn't work at all.
We're in the ballpark for sure!

[Kev]

If my assumption is correct and the Russians did adhere fairly closely to the main construction methods when reverse engineering the GPZ coil, it appears the RX coils are adding and not opposing.

It looks like in both the original and the X-coil the wind has a "clockwise" sleeve to identify which wire is which. Thus the junction coil connections can be surmised from this
On the junction pcb, the clockwise wire of the first coil (assumed sheathed) goes to the cable core and the counter-clockwise end joins to the clockwise end of the second coil (definitely sheathed) and its counter-clockwise end goes to the cable screen.

The double near surface signal with small items is thus likely due to the target inducing a signal as it passes either coil edge, and not from a centre null that would occur with an opposing topology.

[green]

If my assumption is correct and the Russians did adhere fairly closely to the main construction methods when reverse engineering the GPZ coil, it appears the RX coils are adding and not opposing.

It looks like in both the original and the X-coil the wind has a "clockwise" sleeve to identify which wire is which. Thus the junction coil connections can be surmised from this
On the junction pcb, the clockwise wire of the first coil (assumed sheathed) goes to the cable core and the counter-clockwise end joins to the clockwise end of the second coil (definitely sheathed) and its counter-clockwise end goes to the cable screen.

The double near surface signal with small items is thus likely due to the target inducing a signal as it passes either coil edge, and not from a centre null that would occur with an opposing topology.

[ATTACH]50781[/ATTACH]

Interesting you are suggesting Rx coil are adding not opposing. When I made one, adding is the only thing that made sense. Wondered if I missed something. You are the first to suggest Rx is adding that I've seen.

[Kev]

Interesting you are suggesting Rx coil are adding not opposing. When I made one, adding is the only thing that made sense. Wondered if I missed something. You are the first to suggest Rx is adding that I've seen.

Yes I saw your experiments, very informative, thank you very much for sharing those.
From your opposing demonstration I just couldn't reconcile that massive null to what I experience with the machine, it didn't spatially recover like i understand ZED to behave.
I felt it must be an adding arrangement, and looking at the foregoing I think it is probable, I will find out once I start laying it out.

Remember too, this is not your usual detector, without a super D it wouldn't leave the bench.
I could still be wrong of course, time will tell.

[6666]

Yes its all yellow

[Kev]

Yes its all yellow

6666 what makes me think the Minelab one is the same as the Amidon one, is that the actual Minelab one has a clear side, and the Amidon Type 6 is also yellow with a clear side.
T130 is the size and it matches in that respect also, so I'm pretty convinced that an Amidon T130-6 will get you a very close if not a replicate toroid.

Having said that, your toroid may be another manufacturers offering of the same part.
Here's a pic of the genuine model with the clear coat side showing.