mono coil IB

[Aziz]

Hi all !
...

Hi deemon,

nice new proposals.

As I have a second output channel on my sound card, I will compensate the high TX coil voltage with a transformed high voltage compensation signal. So I need a good signal transformer.
Mixing (adding) them together to 0 V (simulating IB condition) will lead to an inherent voltage divider however. So there will be some loss of target response. As I have a High-Q TX resonant circuit, the high impedance of the mixed output may not be loaded further (input impedance of the ADC input) and there will be an high impedance buffer/amplifier (j-fet input).

The signal transformer is quite critical. It depends on core losses, frequency response, maximum voltage transformation factor, etc.

I have up to 6 V on the second channel to transform it to 30 - 60 V or more. I hope, the core and other losses won't lead to heavy temperature drifts.
I have to try it out. It all depends on the quality of the signal transformer.

Cheers,
Aziz

[deemon]

https://pe2bz.philpem.me.uk/Comm01/-.../OtherSite-01/

I think this project is a good example of a mono coil.

This is an old Schedrin's curcuit , I had seen it many years ago , the main concept of the coil compensation is completely different from mine .
By the way , I don't like it , I think that this concept has unavoidable faults ...

[profesor]

https://pe2bz.philpem.me.uk/Comm01/-%20-%20Ion-Photon-RF/-%20Metal-Detectors/-%20BuildPlans/-%20IB/IB-110-Eng/OtherSite-01/

I think this project is a good example of a mono coil.

[deemon]

And then I started thinking about another thing . You see , the versions 1.1 and 1.2 are quite suitable it terms of "ground rejection" , but still has a kind of a drawback . I mean that we need to use an RX coil with less diameter , so we sacrifice some sensitivity in order to get better "bad soil perdormance" . And I've been thinking if we are have a way to remove RX coil from TX without this RX coil "shrinking" ? And then I have found another interesting and quite radical solution . I mean to change a shape of TX coil - to make a ferrite rod antenna unstead of a round coil , so we can now make our RX coil of full diameter , and that must be good This is the version 2.0 on the picture . And "the final cut" is to add a special anti-phase coil L5 ( version 2.1 ) just in the same manner as I did before in the 1.2 version . But here we must realize that usage of ferrite in our TX coil applies some limitations on our TX signal . I mean that due to unlinearuty of any ferrite we must use only a signal with a horizontal top current pulses ( current square wave ) ,,, but for our luck this signal does have already been developed in this topic - https://www.geotech1.com/forums/foru...ulse-induction

[deemon]

Hi all !

After passing some years after the first publication of this mono-coil IB solution I have returned to this idea several times , and I decided now to publish a few steps of evolution of this approach .
Although the first scheme ( topic start ) was good enough - it provides the best sensitivity with the fixed sensor size - there are some other considerations that must be taken into account . I mean a performance of the sensor in a kind of "bad conditions" - very heavy soil with the ferromagnetics particles , metal garbage on the surface , etc . In all these conditions we need to reduce the sensitivity to any kind of ferrite or metal particles NEAR THE COIL . But how can we do it ? The first and quite obvious solution is to separate the TX and RX coils , make the RX coil less diameter - this is version 1.1 on the picture . But even after doing this we still might have some reaction on a little piece of ferrite being moved quite near our TX coil , because some magnetic field lines from this piece might reach the RX coil and produce some additional parasitic signal . So I finally decided to add another coil (L5) , a few turns of wire that have been wound just on the RX coil and connected to the balance chain in anti-phase polarity , so the signal of this coil can cancel the unwanted derrite reaction ( version 1.2 ) .

[moodz]

Since I have been doing alot of work around TX drivers lately .. I thought I would take Deemons "variant 1" and see how it would do on the modified E type driver.

Seems to be OK .... below is a pic of the sim results... ( I intend to try the real thing very soon ).
The TX develops a nice transmit current and the cancellation shows a no target and target response. There seems to be phase and target magnitude being detected by the balanced cancellation.

I dunno if deemon was thinking of wideband square waves or VLF .... but VLF might be a winner.
The spiking is coming from the switch transitions in the E class ... I could filter that .. this was just a quickie sim.

[Tinkerer]

Coil matching circuit

This is a circuit that matches the input of the signal coil that has 316uH inductance
and the compensation coil that has 15uH inductance.

Both coils pick up the TX voltage pulse of 300V, in opposite phase.

The 2 signals are matched and nulled.

Only a very small residual TX signal is left, but the target signal remains and is then amplified.

This circuit does the job, but it could be much simplified and improved.

Any suggestions?

[sinclairuser]

hi all, been reading this and other searched threads, as i still haven't found a coil design that suits my project.
i'm putting a vlf and pi in the same enclosure, for specific tasks, the coil design is where it get troublesome.
i dont care what design i use either as long as it fits in one coil shell, my first idea was to use a foster type pi with high inductance, build the coil ib style, use a vlf that had specs near to the coil then tune the vlf to the coil.
allthough the rough breadboard worked, the pi did not like having the unpowered vlf connected to its coil, so i am now dual switching the two detectors, pi on vlf off and vice versa, both+ and - simultaneously, diodes/caps protect the vlf from the pi circuit at the coil.
its very early days but both boards detect metal and dont detect each other, but its very complex, crude and far from ideal.
so something like a single loop ib coil may help here.
thanks,
aly.

[mickstv]

I am not selling any PCB. I am offering to give you a PCB for FREE.

Thanks for the offer Tinkerer.

Although I'll still see how I go with the TX first. Have you been able to find the schematic for the TX section yet ?

[Tinkerer]

Once I get the TX circuit from you and if I get it working correctly, I might buy a RX board.

Thanks Tinkerer.

I am not selling any PCB. I am offering to give you a PCB for FREE.

[mickstv]

I will look for it.

I also have a few first run PCB's (not populated) of the RX as shown below. Note that there were some mistakes but fixed. Let me know if you want one.

Once I get the TX circuit from you and if I get it working correctly, I might buy a RX board.

Thanks Tinkerer.

[Tinkerer]

I might as well, but I'll have to find up the TEM circuit I built first. To you have a circuit for the modified TEM TX ?

I will look for it.

I also have a few first run PCB's (not populated) of the RX as shown below. Note that there were some mistakes but fixed. Let me know if you want one.

[mickstv]

If you feel like experimenting, we could use a modified TEM TX, (continuous current, non reactive sample time)

I might as well, but I'll have to find up the TEM circuit I built first. To you have a circuit for the modified TEM TX ?

[Tinkerer]

Yeah I had the same problems when I was working on the TEM and trying to compensate on the TX side.

I might try the RX side compensation. Set it up with manual control first, then try to work out an automatic control.

If you feel like experimenting, we could use a modified TEM TX, (continuous current, non reactive sample time)

[mickstv]

Here is the complete preamp circuit to the ADC

Thanks Tinkerer.