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

[Aziz]

Ok, I have found the bug in the system.

No real bugs! LTspice, AI and my coil software is working fine.

Wrong parameter. I have forgotten to set the proper target coils resistance.

Everything is fine now.

I can simulate a mono coil VLF model to check, what we can expect target responses. This will help to set the j-fet amplifiers gain.
Aziz

[Aziz]

Hi all,

I am quite confused.

I have found a serious bug either in LTspice XVII(x64) (17.0.37.0) or in my coil software.

Following situation:
Coil simulation for target response: TX -> Target -> RX
Simple circuit simulation: giving L1 (TX), L2 (Target), L3 (RX) = L1 and coupling coefficient k (L1, L2), same k for (L2, L3)

The interesting fact is, that the AI and my coil software delivers same results.
My coil software must be halucinating too. Maybe I am hulucinating much more.

LTspice simulation is delivering exactly 100 times less target response. WTF!, what is going on?


I have to fix this issue.

[Qiaozhi]

Aziz abi merhabalar,

Amatör bir dedektör hobicisi olarak, bu işin donanım tarafına hakim insanlarla sohbet etmek ve sorularımı yöneltmek istiyordum. Sizle daha kolay konuşabilmek adına bir iletişim adresiniz var mıdır? Numara ya da mail.

Teşekkürler.

Please read the forum rules -> Basic Rules of the Forums
and make your posts in English.

[kbsurmeli]

Aziz abi merhabalar,

Amatör bir dedektör hobicisi olarak, bu işin donanım tarafına hakim insanlarla sohbet etmek ve sorularımı yöneltmek istiyordum. Sizle daha kolay konuşabilmek adına bir iletişim adresiniz var mıdır? Numara ya da mail.

Teşekkürler.

[Sergey_P]

Hi, alex
Changing the signal frequency changes the impedance due to changes in the reactive component's resistance. The active component (R) is independent of frequency.
Energy is expended on the active component (R), so matching between the source and load occurs at the R level.

[alex.drozdov]

Удельное сопротивление Грунта (чернозем, суглинок...) в зависимости от влажности меняется в очень широких пределах(10...150ом/м). Примем что-то среднее =75ом/м

На катушечном калькуляторе с размером катушки 150мм имеем примерно
137витков, провода 0,25мм, Rкат=24ом>>

Rac changing with frequency, 75ohm/m and 24ohm can used only for DC.

[Aziz]

Oh man!,

Google AI (Gemini) does make so much serious errors in schematics analysis and design.
Claude AI didn't give me any answer and has reached the time limit.

The j-fet amplifier design must be finished by hand.
I will raise the drain current to 3 - 4 mA as it will operate in a lower noise mode and the power consumption is not much for a 9V block battery (it is a compromise only).
Gain of 4 - 8 would be enough.
Aziz

[Aziz]

Yeah,

it also works perfect with 8 turns for the primary coil. Each coil section has 1 turn primary coil winding now.
7 Vp input voltage is being transformed into 140 Vp (280 V span!). 1:20

But for above 12 kHz.

Below 12 kHz, the distortion happens (delivering not enough primary coil current). Too low primary coil inductance too.
I will use frequencies between 24 - 48 kHz and this isn't going to be a serious problem.

It seems, that we can get almost all of the target response out of the mono coil in VLF mode.

I have to test the thermal conditions yet. But I think, it will cause temp drifts at extreme levels.
We will see it.

[Aziz]

Hi all,

my 1:10 signal transformer is working fine (above 3 kHz). Below 3 kHz, signal distortion and high current protection circuit triggering happens (connected it directly to the line output without any current limitting feature).
Bandwidth is high enough: Tested up to 86 kHz with a 220 pF capacitive load without any distortion or resonance effects.
Above 86 kHz, the sound card produces more phase noise and low output voltage.
The output voltage at high-gain mode is 70 V peak with 220 pF load (+/- 70 V). Input is 7 Vp (+1 V more ).
So we can go with the TX voltage up to 100 Vp or even more.

I will do the simple primary current limitting resistor (10 - 47 Ohm) in series with the signal transformer to be in the save region. This is the cheapest solution.

I should test the signal transformer with 8 turns for the primary coil for 1:20 voltage boost. Let's look, what happens. (Best case: TX voltage up to 200 Vp).
And I should measure the ferrite core loss / magnetisation current.

The mixer capacitors need to be FKP1 and high voltage (min. 400 V=).

Cheers,
Aziz

[Sergey_P]

Hi, Azis!
You were looking for something unusual in this thread—and I happen to have exactly what you need: inductive balancing devices + a bipolar square-wave AC signal + real-time target signal analysis.
The device features low power consumption, is independent of (or depends only negligibly on) the input signal level, enables target signal detection against a noise background, and boasts high resolution (dT = 1 µs).
The signal received from the target "colors" the noise of the broadband amplifier (which ensures the 1 µs resolution); subsequently, statistical methods and a correlator are used to extract and display the probability of the useful signal's presence. In this prototype—unlike the background noise—the useful signal is encoded using a phase-modulated M-sequence 255 bits in length. At present, no analogues to this type of detector are known to exist.

Top to bottom (time scale: 1 µs to 64 µs):
1. Sensor
2. Aluminum
3. Copper
4. Ferrite
5. Iron
6. No targets present
Distance to target: ~15 cm

[Aziz]

Hi all,

if the signal transformer does cause too much problems (temp drift, low bandwidth, low voltage transforming, etc..), I will go to the second best option without any transformer.
Doing the chancellation with 6 V only. The TX coil voltage will be limitted to 30 - 60 V. So the mixer would attenuate the target signal 5 to 10 times.
And we have the j-fet amplifier to compensate the target signal attenuation. A gain up to 10 times would be enough.

I am sure, it isn't really required to wind the signal transformer. It is difficult and expensive part.
Anyway, I'll test both options.

Let's tweak the j-fet amplifier and let the AI expressing its opinion. Claude AI does support LTspice files too.
I have to build the j-fet amplifier part next time.
Aziz

[Aziz]

Hi all,

I have wound the signal transformer finally. It was quite difficult.
Voltage step up of 1:10 (16 turns -> 160 turns).
I have a very good coupling coefficient k and very low stray inductance (1.7 µH, k=0.9997). This is excellent.
I have divided the secondary coil windings into 8 sections with 2 mm gap. 4 mm gap for secondary coil endings. This should make the coil capacitance low and the bandwidth of the signal transformer high.

But I have to test it yet.
Aziz

[Aziz]

Hi Sergey,

I had difficulties in translating your post. Google translate failed. But Claude AI did it at the end (with readable formulas).

With a low Q system, you will have less problems (and less sensitivity). This is the reason, why everyone avoids having big problems.

But I can cope with all the problems happening in the high Q systems. And I get really a very good detection performance.
Aziz

[Sergey_P]

Hi Aziz
<1. Limited power supply>
A technically solvable problem
<2. Narrow bandwidth (< 100–200 Hz)>
Insignificant; the detector bandwidth is 20...40 Hz
<3. High sensitivity>
of the high-Q circuit to coil parameters
<4. Operating principle based on detuning relative to resonance>
Discussed below...

A high-Q circuit is characterized by an impedance mismatch relative to the ground. Ground material located in the immediate vicinity of the sensor coil induces phase noise within it, which masks the useful signal.
To reduce phase noise caused by ground effects, there are three options:
1. Low quality factor (Q) of the sensor's resonant circuit: Q ~ 5
2. Non-resonant sensor
(based on materials from md4u.ru):
<<Грунт обладает электрическими и магнитными свойствами и воздействуя на приемную катушку изменяет её параметры. Эти изменения выражаются как внесение дополнительной индуктивности и сопротивление потерь в параметры катушки. В случае безрезонансной RX катушка представляет собой LR-цепь фазовый сдвиг в которой определяется выражением ф=arctg(w*L/R). Если в присутствии грунта w*(Lкат+Lгр)/(Rкат+Rгр) будет равна w* Lкат/ Rкат, то фаза останется неизменной.
w* Lкат/ Rкат - это добротность катушки, Qкат,
w* Lгр/ Rгр - это добротность грунта, Qгр. Фазовый сдвиг грунта (АКА Сигнум) разместил порядка 86гр , что соответствует Qгр ~14
Удельное сопротивление Грунта (чернозем, суглинок...) в зависимости от влажности меняется в очень широких пределах(10...150ом/м). Примем что-то среднее =75ом/м в размере нашего поискового поля =33см имеем Rгр=25ом
Для согласования сопротивлений для максимума передачи энергии примем: Rкат=Rгр=25ом
на частоте 8кГц ->
L=Q*R/w=14*25/(2*pi*8000) =7000мкГ
На катушечном калькуляторе с размером катушки 150мм имеем примерно
137витков, провода 0,25мм, Rкат=24ом>>
3. Operation with detuning relative to resonance
(based on materials from md4u.ru):
<<В МД приемный резонансный контур изображается в виде параллельного контура расстроенного по частоте, но на самом деле источником ЭДС является сама катушка!, т.е. источник эдс включен _последовательно _ с последовательным колебательным контуром RLC.
Критерии те же самые: добротность (Q) и фазовый сдвиг (ф), калькулятор вам в помощь ->

https://www.translatorscafe.com/unit-converter/ru-RU/calculator/series-rlc-impedance/

например:
L=12мгн, С=0,1мкф, R=25ом, F=8кгц получаем -> Q~14, ф~86гр, Fконтура резонансное=4,5кгц, что соответствует катушке -> диаметром 150мм, проводом 0,28мм, имеющей 185 витков...
(калькулятор катушек -> https://esm62.ru/calculator/raschet-...uctql546374216 ) >>

[Aziz]

Hi Sergey,

Hi Aziz
Sound BlasterX G6 -> https://reference-audio-analyzer.pro....php#gsc.tab=0
OK
What is high Q-factor used for? Is it preferable to focus directly on the signal from the target, rather than on changes in coil parameters caused by ground effects?

There are several reasons for using high Q resonant tank.
1. Limitted power source:
Sound cards don't give enough power to drive the TX coil. High Q factor will amplifiy the source current by a factor Q.

2. Narrow bandwidth: ( < 100 - 200 Hz)
The TX coil will pickup less noise.

3. High sensitivity:
The TX coil will respond to targets and ground with high sensitivity. Very small changes will lead to big changes to the TX coil voltage (amplitude, phase shift) .

4. Acting like an Off-Resonance principle:
Targets will "steal" energy from the TX coil. Any tiny energy loss will lead to big changes (amplitude decrease, phase shift).

These basic facts will lead to a good detection sensitivity and depth on a mono coil at the end.
Aziz