Ideas to tinker

[Tinkerer]

Thanks Tinkerer, it looks clearer now and the use of a balanced coil is justified.
As Eclipse says, the TX width must keep a certain relationship with the frequency, so that it does not oscillate, I think of a relatively higher frequency than traditional PIs.
I would like to see how the EFE field is controlled, or the GB, but I already asked many questions. Thanks again.

I used to take 5 to 10 sample windows, then add or subtract the windows among each other.

The 0 crossing is the important spot in time. Before the 0 crossing, you see the decay of the targets.
After the 0 crossing, you see the "target charge".

The full interaction of the magnetic pulse with the target during the whole cycle is complex and I don't know how to explain it.

Maybe if somebody who is good at drawing could try to put my explanation into graphics it could become understandable.

Of course it could be explained with mathematics. We can see that LTSpice calculates perfectly what is happening. Unfortunately this is way beyond my capability.

[green]

Interesting experiment.

This is not TEM. TEM recycles the Flyback power. This makes it more power efficient than traditional PI.
The side effect is that it becomes more VLF like. I have run it with up to 15 Amps peak current, (real circuit, real 6ft diameter coil, #10AWG wire) at high repetition rate, while consuming a fraction of what a traditional PI would consume.

Are you looking at right side circuit?

[Jose]

TEM. reminds me of horizontal TV output with TRC.
I have seen some TVs, which worked with the horizontal output transistor without heat sink.
I also remember that they had efficiency diodes in parallel, the horizontal frequency was 15625 Hz and the pulse width was 64 us. just to get an idea of how often it can operate.

[Tinkerer]

Are you looking at right side circuit?

This one is right. the one before had a 1420 Ohm damping resistor.

[green]

I would like to see how the EFE field is controlled, or the GB, but I already asked many questions. Thanks again.

I'm wondering about EFE and GB also. Maybe TEM is better if the coil is stationary, detecting moving targets?

[Tinkerer]

I'm wondering about EFE and GB also. Maybe TEM is better if the coil is stationary, detecting moving targets?

I tried to apply the method to stationary systems, like "Ground Loop", where a large TX coil is laid on the ground and then one walks within that loop with the RX coil. Tried this with a loop of 20 meter diameter. Run into the problem that the field strength within the TX loop is not uniform. I varies between the center and the rim.

Trying to layout 10 sample window signal paths in analog finally got so complicated that I searched for a digital solution.
Could not find any help for DSP. DSP needed real programming skill, whereas I just barely managed to setup a sequential timing schedule for an 8bit PIC.

Tried several other methods, more about that later.

[Tinkerer]

philosophy

Before we get deeper into the circuits, I would like to talk a bit about my philosophy of tinkering.

We started off with a traditional PI TX circuit, "in the box". The limiting factors are the coil turns and inductance, coil capacitance and peak flyback voltage. Basically the "brick walls" of the box.

for people less familiar with the "jargon": a "brick wall" is a big problem. An insurmountable problem. No way over it, no way around it no way under it.
So here comes the philosophy again:

Every problem is also an opportunity. An opportunity to solve the problem.

Going back to the PI TX capacitance problem: Everything has been tried to reduce the capacitance. Over the recent years some progress has been made, but we are at the "brick wall" of the PI TX capacitance.

The opportunity? More about that later.

[green]

https://www.geotech1.com/forums/atta...9&d=1596044550
Right side circuit(TEM)isn't correct. Spice simulation doesn't avalanche MOSFET so coil decay is faster than should be.

[Tinkerer]

Attached is the simulation with a few changes to make it fit the Mosfet, without avalanching.

With the desired design parameters, we could design it specifically.

[Tinkerer]

TEM TX CURRENT

This is what the TX current looks like. A deceptively simple saw-tooth wave.

In fact it is very complex. We will look at the complex details in days to come.

[eclipse]

Do you think it's possible to get a bipolar TEM with a single coil? Since current is flowing through the whole TX cycle maybe that's not possible? What do you think?

[Tinkerer]

Do you think it's possible to get a bipolar TEM with a single coil? Since current is flowing through the whole TX cycle maybe that's not possible? What do you think?

How much bi-polar do you want it to be?

I added a Zero Amp line to the picture. Positive on top, negative below.

Not quite symmetric? Play with the parameters to make it symmetric.

However, You still need an RX coil and a way to reduce the TX pulse on the RX coil. There are several methods to do that. DD, concentric with bucking coil, passive compensating coil, Active controlled compensation coil, etc. You can also find several patents, some old and some more recent of how to do that.

[eclipse]

Even if made symmetric it's still not bipolar. I'm just looking a way to eliminate EF cancellation.

[Tinkerer]

Even if made symmetric it's still not bipolar. I'm just looking a way to eliminate EF cancellation.

HA HA, Maybe I should have said "arguably bi-polar"? If I look at one half cycle, I see a triangular wave from zero Amps to +500mA.
The second halve period goes from zero Amps to minus 500mA. Just like an AC wave goes. Is AC bi-polar?

Any opinions?

[green]

HA HA, Maybe I should have said "arguably bi-polar"? If I look at one half cycle, I see a triangular wave from zero Amps to +500mA.
The second halve period goes from zero Amps to minus 500mA. Just like an AC wave goes. Is AC bi-polar?

Any opinions?

Zero to 500mA, -500mA to zero. Both halves, increasing slope.