About pulse emission and ground balance

[dbanner]

Actually, when coils are wound in opposite directions with the same polarity current driving them, the coupling is reduced, not increased.
That's because the fields are opposing. But in this case, the pulses are asynchronous, so technically the reflected fields are aiding and so the coupling is stronger. So I'm OK with that.

The statement that the coils have resonance that harmonize, simply means two identical coils ie, same guage wire, same number of turns, same SRF. The coils being wound bifilar seems to fit the bill.

[dbanner]

Now here comes the nail biter. Although the coils are wound in "opposite directions", they never "see" each other as such. When TX1 is on, L2 is aiding the field of TX1. When TX2 is on, L1 is aiding the field of TX2. The reflected energy is of the same polarity, but the ground is cancelled by the reflective coupling! even before it reaches the opamp.
My previous statement about summing is rubbish, its all achieved in the coils themselves, me thinks.

Time to go put an ice pack on the head.

[eclipse]

How about the claim that this method provides discrimination capabilities?

[Orbit]

I would say yes to such cancels ground , and it makes sense I worked something like ..It's canceling immediately at the output of the comparator, comparator must be low noise, low drift and and high gain !"
Many years ago I had a scheme with with two transfer coils I searched but can't find it used two 555 oscillators who were operating at the same frequency but with different pulse widths...I'm also with two bifilarly wound coils I found a way to coil detects only in one direction or below above is not detected metal!
That was experimental which I didn't finish until the end the only thing my coils were heating ...

[6666]

I would say yes to such cancels ground , and it makes sense I worked something like ..It's canceling immediately at the output of the comparator, comparator must be low noise, low drift and and high gain !"
Many years ago I had a scheme with with two transfer coils I searched but can't find it used two 555 oscillators who were operating at the same frequency but with different pulse widths...I'm also with two bifilarly wound coils I found a way to coil detects only in one direction or below above is not detected metal!
That was experimental which I didn't finish until the end the only thing my coils were heating ...

Thanks Orbit.

[green]

First pulse 1 = + V + GROUND EFFECT (g)
then pulse 2 = - V + GROUND EFFECT (g)

reception was Pulse 1 rx = + V + s or "s" is ground effect
then Pulse 2 rx = + -V + s

then by (pulse 1 - pulse 2) it gives + V + V + g - g = + 2V and "g" has disappeared !!post From first post, Manta Metal Detector https://www.geotech1.com/forums/show...419#post217419

Why doesn't the ground signal invert when target signal inverts. Looks like just what thread was looking for, a way to ground balance without a hole.

[Orbit]

Earthy signal always seeks to establish a balance without actually metals the output is zero when lowering or raising the coil at the output of the comparator! Only in the event that there is a metal below as the target signal is stronger we get a target signal at the output , that is, a scale it is no longer in balance !!The translator may not translate correctly so you may not understand me , I'm not talking without a connection, (it really works)!

my experiment is similar to that of Maita that is, the Manta transmitter only i have tried the receiver differently , that there is no target signal loss if it is a single channel!

[Altra]

I think you are hoping for something that is impossible. The ground signal is the same as a target, it is a result of induced currents. If it nulls out the ground, it will null out the targets. In bi-polar you get ef cancel because it is unaffected by the induced currents and does not change polarities. Ground balance on bi-polar is just like any other pi except you can ignore the ef. early target minus later GB signal.

@Green the ground does invert. So it's not a break through for GB

MicksTV presented a similar(Manta) PI circuit using a center tapped coil. Unfortunately Mick would upload his schematics and photos to hosting sights and many are lost now.

[6666]

I think you are hoping for something that is impossible. The ground signal is the same as a target, it is a result of induced currents. If it nulls out the ground, it will null out the targets. In bi-polar you get ef cancel because it is unaffected by the induced currents and does not change polarities. Ground balance on bi-polar is just like any other pi except you can ignore the ef. early target minus later GB signal.

@Green the ground does invert. So it's not a break through for GB

MicksTV presented a similar(Manta) PI circuit using a center tapped coil. Unfortunately Mick would upload his schematics and photos to hosting sights and many are lost now.

Hi Altra, I miss mickstv's posts, is this the one you were thinking of ?, I may have another here somewhere.

[Altra]

Hi Altra, I miss mickstv's posts, is this the one you were thinking of ?, I may have another here somewhere.

Hi 6666, yes that's the one, thanks for posting it. He also posted a p-channel version with a differential pre-amp. The only difference between the Mick's drawing and the Manta. Is the series diodes are replaced with mosfets in the Manta. These block the opposing flyback voltage from going back into the low voltage supply, just like the series diodes.