Induction Balance Stuff - Single/Multi Frequency Response, GB, Disc, Measurements, Ideas, Fun, etc.

[Aziz]

PS:

On very mild ground mineralsation:
It can be operated at single frequency in differential mode.

On heavy to severe ground mineralsation:
Two frequency mode (f1, f2) -> 4 I/Q vector processing required.

[Aziz]

Hi all,

this is my latest KISS Dual-Frequency Induction Balance VLF Detector Controller for sound card use.
Operated at moderate power consumption in high-gain mode of G6 (mid-level output, TX coil voltage up to 100 Vp).
The Q of the LC tank is still high enough (approx. 10).

At maximum output level (7 Vp), the TX coil voltage will go up to 250 Vp and the sound card may get hot too. It is very likely, that it switches itself off due to high current protection triggering.
Anyway, this is a KISS power beast.

The search coil is an IB coil. You will get very high sensitivity and depth.
The very sophisticated digital signal processing will also allow operation of heavy ground mineralisation.

All parts must be placed inside the coil housing. The coil cable bears only low voltage and low current and can be a thin and flexible shielded stereo earphone cable (2x Stereo, Input, Ouput).
You need low loss, high voltage rating FKP (Foil) capacitors.


Cheers,
Aziz

[Aziz]

I forgot to mention:

The feed-in can be also made with rectangular pulses (PWM output of MCU). Take a simple push-pull driver (a two channel mosfet driver) with external power supply and you are on game.
The mosfet driver delivers enough power for this purpose.
This project can be well fitted fully into an embedded MCU project (STM32.. ) .

Aziz

[Aziz]

Hi all,

ground loop systems are really not much practical to use. Especially on virgin ground.
But a larger portable frame coil is the next best option.

------
Back to my previous dual frequency VLF:

TX coil (either mono or IB):
Thick litz coil wires for High-Q LC tank are going to be a problem with the cabling.
Best option is to keep the thick litz coil wire inside the coil housing. And the parallel tuning capacitor Ct too. So the huge current keeps flowing inside the coil housing and not through the cabling system. The feed-in cabling can be thin wire (low current flowing).
The two series capacitors and the two resistors for the voltage divider fits into a thin plastic tube (must be shielded). No bread board required at all.

Well, I could take much thicker tinned litz wire for the TX coil now (min 2.5 mm²).
Max Q, max bang, max sensitivity, max muscles (heavy TX coil ).

I could rise the Q back again (Q > 60 or more).

It doesn't matter, when the LC tank is out of tune due to heavy ground mineralisation and TX inductance change.
We have two frequencies f1 and f2. And they can be adapted to ground conditions.

Aziz

[Aziz]

The only problem will be the free-running LC-oscillator (phase/frequency instability may be too much).
But this can be replaced with a programable frequency oscillator (crystal source, adjustable to ground mineralization, via MCU).
With blutooth-link.

[Aziz]

Hi Paul,

Its been done and patented Aziz .. woody did one some time ago.

No problem.
It will be a fully different technology. It's a VLF not pulse induction. Nor synchronized to the transmitter.

A very simple one:
High power, single frequency, stable and free running LC-Oscillator with a big ground loop (10 - 20 m or larger diameter).
No cables to the detector at all. The power transmitter with big battery can be placed on the ground.

The detector consists of only an anti-interference concentric co-axial (small) RX coil (+ processing unit).
Single channel, single frequency VLF processing.
Hilbert-Transform or SPLL with phase-tracking info.

TX coil current may be 1 - 5 A. TX voltage can go 500 - 2000 V (depending on the capacitors). Better a High-Q TX LC-tank for more power efficiency.
The TX coil won't "detect" ground response: it isn't changing its inductance anymore when it is placed on the ground.

Most of the time the RX coil will pickup in-phase response (X-response). This is due to coil coupling change during swinging and changing position. This can be handled.
Any off-phase response is target response (R-response).

This is feasible.
You may ask your AI mate too.

A ground breaking big deep gold monster chaser.

Cheers,
Aziz

[moodz]

Hi all,

lets think of big, bigger and max!

I wonder, whether it is possible to operate the High-Q VLF detector as a Ground Loop VLF detector.
5 m or more diameter coil layed on the (severe mineralized) ground. The operating frequency can be set to the ground conditions (automatic).
A thick 3 or 5 core power cable can be realized as TX coil (all cores connected in series to form a big TX coil).
A thin cable for TX coil powering (due to High-Q, less power drain is required).

A second smaller coil as RX (20 - 30 cm diameter). The real search coil.
There won't be high voltage induced there. But the RX coil will pick-up target resonse. And the local mineralisation change. Plus the coil position change (pure X-response).
Searching inside the big TX coil.
X-response due to search coil sweep can be really handled.

I have to ask the AI sometime...
Aziz

Its been done and patented Aziz .. woody did one some time ago.

[Aziz]

Hi all,

lets think of big, bigger and max!

I wonder, whether it is possible to operate the High-Q VLF detector as a Ground Loop VLF detector.
5 m or more diameter coil layed on the (severe mineralized) ground. The operating frequency can be set to the ground conditions (automatic).
A thick 3 or 5 core power cable can be realized as TX coil (all cores connected in series to form a big TX coil).
A thin cable for TX coil powering (due to High-Q, less power drain is required).

A second smaller coil as RX (20 - 30 cm diameter). The real search coil.
There won't be high voltage induced there. But the RX coil will pick-up target resonse. And the local mineralisation change. Plus the coil position change (pure X-response).
Searching inside the big TX coil.
X-response due to search coil sweep can be really handled.

I have to ask the AI sometime...
Aziz

[Aziz]

Hi Sergey,

<High-Q LC-tank (of approx. 30 in my case).>
A change in the ground signal level causes a phase shift in the resonant circuit due to the change in its parameters, not due to the induced signal from the ground/targets. This phase noise will interfere with target detection and cannot be compensated for.

but I can do it. There are more ways to do it. Note, that I have 2 / 4 I/Q vectors for processing.
A robust mono/IB-coil VLF design in severe ground conditions is possible.
Even with an extremely High-Q design.

[Sergey_P]

<High-Q LC-tank (of approx. 30 in my case).>
A change in the ground signal level causes a phase shift in the resonant circuit due to the change in its parameters, not due to the induced signal from the ground/targets. This phase noise will interfere with target detection and cannot be compensated for.

[Aziz]

The AI says, that the Hilbert-Transform -> Envelope -> FFT
isn't really required.

The Goertzel demodulation (or Lock-in amp) delivers enough and more efficient information for GB and target detection.

This is quite a funny chat.

I should do more chat with the AI.

[Aziz]

Hi all,

I am chatting with the AI about the Hilbert Transform, envelope extraction and FFT of the envelope.

It says, that the mono coil VLF with dual-frequeny mode around the resonant frequency will work on severe ground conditions (iron ore gold fields).
Even there is a High-Q LC-tank (of approx. 30 in my case).

Well, let's look at this feature in detail.... a quick & dirty hack to the software is required..
My mate Donald is going to be very very rich soon ...

[Aziz]

Hi all,

I have now the decoded 4 I/Q vectors visible. I'm using the Goertzel as it is the most efficient.

All the ground and target information is there now.


I have observed a nice and distinc response change on the intermodulation frequency (in my case 100 Hz).
Especially on the envelope curve of the intermodulation frequency.
The X-response differs from R-response.

One possible way to process a single channel:
Hilbert Transform -> Envelope -> FFT of Envelope

FFT delivers the frequency spectrum of the envelope. Note, that the FFT is being used for the very narrow band intermodulation frequency. We get a much finer frequency resolution. Whole spectrum response in the 100 Hz bandwidth is visible.
Using only the magnitude spectrum of it, we can use the linear combination method to get rid of the ground response (simple processing variant).
We also could use phase spectrum too. Or an array of complex I/Q vectors.

But this isn't really required.
The decoded I/Q vectors deliver enough information for simple processing too.

Aziz

[Aziz]

Hi all,

BTW, the high sensitivity of the TX LC-tank to ferrite/hot ground is fully intended. It is not a bug, it is a feature! We get very valuable GB info.

So how can we still use a mono coil TX? Without induction balance?

This is really trivial.
We could use a quasi mono coil design.
Round main mono coil as always used before + a few turns smaller concentric co-planar secondary coil, fed into the other channel.
The second coil has less coupling coefficient (k < 0.1) and hence will induce less voltage. But enough to process the signals.

The hot ground mineralisation will modify (increase) the coupling coefficient k. There we get the GB info. We can remove the ground response content in the main mono coil signal.
Of course in dual-frequency mode. 4 I/Q vector processing.

The quasi mono coil is quite easy to build and is not critical.
Aziz

[Aziz]

Hi all,

the circuit needs to be optimized further.
In order not to attenuate the line input level in the sound card much (due to big TXref and small RX coil signals), the TXref signal needs to be divided by a simple resistor voltage divider. So two resistors will be added further. Thats all.

This will be my ultimate ground breaking VLF-IB detector.
It will even operate on pure iron ore grounds (severe ground mineralisation).
Note, that we are not fixed to the in-air resonant frequency. We can adapt it for severe ground types. And the frequency distance (df = f2 - f1).
So it will cover some ground mineralisation variation too.

And we can push up the TX power as we have the voltage divider for the TXref.
The Sound BlasterX G6 can deliver at least up to 100 mA current @ 7 Vp output for each channel (but it gets hot).
We can have way above 100 Vp TX voltage. But this is really not required.

A source current of 20 - 50 mA is enough. Multiply this with Q and we have the TX coil current peak.

Aziz