Experimenting with Half Bridge Bi-Polar Transmitters

[Altra]

Recently when White's Electronics announced it's closing. The subject of "Truncated Half-Sine" PI detector was brought up by Carl and a few others. So I wanted to see what it was about after passing over it for many years. Having some success I decided to share my experiments with the forum. In addition, I thought it would be better in a report format versus multiple forum attachments and post. It covers three variations of the Half Bridge Bi-polar transmitter. If you see any wrong assumption or have questions let me know. If we are lucky maybe Carl will chime in on the subject.

[Carl-NC]

Nicely done! You described the same path I took in exploring this.

The IB coil requirements are exactly the same for THS as for VLF except that you need to be careful of high-frequency capacitive coupling. In a sinusoidal system the IB coil is only concerned with one frequency. THS is more like PI, so even if you have good balance for the primary half sine frequency you also have to worry about the fast turn-off slews.

I proceeded to a full H-bridge design to allow switching in more than one series cap and creating multi-frequency THS. I suppose you could still do that with the half-bridge approach by swapping the series coil and cap and switching in different caps.

I hope this goes somewhere, I really enjoyed working on this design. I had a full ground-hunting prototype running that was beating the pants off the TDI, and almost had ground tracking and full discrimination working. Depending on what happens to White's, I may dive back into this myself.

[waltr]

Thanks for the report Altra.
Will study this.

[Altra]

Nicely done! You described the same path I took in exploring this.

The IB coil requirements are exactly the same for THS as for VLF except that you need to be careful of high-frequency capacitive coupling. In a sinusoidal system the IB coil is only concerned with one frequency. THS is more like PI, so even if you have good balance for the primary half sine frequency you also have to worry about the fast turn-off slews.

I proceeded to a full H-bridge design to allow switching in more than one series cap and creating multi-frequency THS. I suppose you could still do that with the half-bridge approach by swapping the series coil and cap and switching in different caps.

I hope this goes somewhere, I really enjoyed working on this design. I had a full ground-hunting prototype running that was beating the pants off the TDI, and almost had ground tracking and full discrimination working. Depending on what happens to White's, I may dive back into this myself.

Thanks for the feedback. I was unable to get a flat line on the RX while trying to null two opposing and spaced full half-sines. Is this possible? By the way I like "THS". This thread should be renamed "EWHBBPT"

[Carl-NC]

I was unable to get a flat line on the RX while trying to null two opposing and spaced full half-sines. Is this possible?

It is. Keep in mind that you are pushing 5-10x more current than is usual with VLF, so the null will need to be 5-10x better.

[Mdtoday]

Great work Altra!
Thanks for sharing.

[Elliot]

This thread is very timely. I was just reading this Truncated Sine Wave Pi patent the other day. It seems the best of all worlds if you can get it working.

[eclipse]

The author of the aquamanta (formely Manta) claims his method is better than the Whites patent.
This statement was made in the geotech forum if I remember correctly.

[ivconic]

... I had a full ground-hunting prototype running that was beating the pants off the TDI, and almost had ground tracking and full discrimination working.. .

Quite bo(a)ld claim, kid!
Are you close?
We can meet here at my place and see what is all about:




P.S.
Nice job Altra!

[Altra]

The author of the aquamanta (formely Manta) claims his method is better than the Whites patent.
This statement was made in the geotech forum if I remember correctly.

I believe he was referring to his method being better than the TDI, not Carl's patent. It was a bi-polar Tx using a center tapped coil. His research has resulted in the Fisher AQ which is a work of art. The TDI, AQ and Manta do not have a capacitor in series with the search coil. This is an important difference.

[eclipse]

I remember he wrote something like "better than whites patent #" and the TDI I don't think has any patents.

Well here's the quote so

"This system is better than US9285496B1 Patent of CARL / Less capacitance, lower noise, best heat dissipation, faster delays, etc ...."

https://www.geotech1.com/forums/show...419#post217419

[Altra]

I remember he wrote something like "better than whites patent #" and the TDI I don't think has any patents.

Well here's the quote so

"This system is better than US9285496B1 Patent of CARL / Less capacitance, lower noise, best heat dissipation, faster delays, etc ...."

https://www.geotech1.com/forums/show...419#post217419

You are right, I didn't remember his quote. But I did remember his schematics in the first post and there are no capacitors in series with the coil. Maybe he has a secret THS system that he didn't post or he didn't read the patent? Anyway it's not important "Who's" is better.

[Orbit]

My experiment promises for now...with a little finishingI think Alexander hides things about his new TX design!

[Orbit]

Bi.Polar .VLF

[Ferric Toes]

This poster looks relevant http://zonge.com/wp-content/uploads/2013/07/TEMposterA.pdf