Autotransformer coil

[Pep_T]

Hi everyone,
I am interested in autotransformer coil since I want to make one for a vlf design. All I know is that they allow high voltages across the TX coil but I know no practical way to make one or how to drive one. What's for sure is that it needs to be made with a center plugged winding but... what else?
Can anyone provide me more material about it?

Also, why they seems to be rarely mentioned and/or used? As far as I can tell ITMD4 did not mention them

Thanks everyone!

[Carl-NC]

23.2 (p445) talks about the differential driver. It's basically uses an autotransformer effect although it's never specifically called that. Now that I look at it again, I think Fig 23-11 is wrong.
You can easily make a differential coil for VLF (see Fig 9-11) but I'm not sure I would say it's an autotransformer. You could also drive a true autotransformer coil and use the open side to create a high voltage, but what would you do with it?

[Mario-j23]

Hi. Search the forum for a Nautilus or Aquasound diagram. Jery Tyndal used a high voltage TX coil in the DMCIIb. I also know the Polish All-1 detector. You will find it in the Kt archive. The Teknetick T2 also seems to use a coil with a tap.
You must use a Hartley generator and the coil must have a center tap.
Such a coil is made by winding two wires at once. Then you connect the end of one coil to the beginning of the other and this is the tap.
I don't know the reasons why they were rarely used.

[Altra]

This patent uses a non-symmetrical tap to create a high voltage tx. Years ago based on this patent I was able to create a 130v tx signal, It was impossible to null the rx coil. Maybe using some feedack between the TX--RX would help? In the patent he states using super hetrodyne method to demodulate the Rx.

[Pep_T]

23.2 (p445) talks about the differential driver. It's basically uses an autotransformer effect although it's never specifically called that. Now that I look at it again, I think Fig 23-11 is wrong.
You can easily make a differential coil for VLF (see Fig 9-11) but I'm not sure I would say it's an autotransformer. You could also drive a true autotransformer coil and use the open side to create a high voltage, but what would you do with it?

Well I did not remember fig 9.11 but it looks just like what I am looking for. This whole story started because I bought a second hand nokta Legend LG28 coil (for a very low price) and trying to reverse engeneer the windings I came to the conclusion that there is a center plugged tx coil, hence the search for a driver for such configuration (who knows how nokta drives it, maybe an H bridge with dual supply?), and the autotransformer came up. Such coil tho uses a bipolar coax cable where the sleeve is connected to the central plug. I think I will try and modify the circuit on fig 9.11 with PNP in order to connect the center plug to ground. I did not initially linked the topics on 23.2 to the autotransformer, I will read them again more carefully. Thanks!

Hi. Search the forum for a Nautilus or Aquasound diagram. Jery Tyndal used a high voltage TX coil in the DMCIIb. I also know the Polish All-1 detector. You will find it in the Kt archive. The Teknetick T2 also seems to use a coil with a tap.
You must use a Hartley generator and the coil must have a center tap.
Such a coil is made by winding two wires at once. Then you connect the end of one coil to the beginning of the other and this is the tap.
I don't know the reasons why they were rarely used.

I suppose that winding two wires at once is needed in order to have both coils on the same plane. Anyway, i took a look at the designs you suggested and they are pretty complex, with multiple tapped coils. Not really want to dive into that hahahaha. Thank you very much, I hope I will have time to go deeper into the topic.

This patent uses a non-symmetrical tap to create a high voltage tx. Years ago based on this patent I was able to create a 130v tx signal, It was impossible to null the rx coil. Maybe using some feedack between the TX--RX would help? In the patent he states using super hetrodyne method to demodulate Rx.

This patent schematic is actually helping me understand the principle behind this. Looks like the "smaller" winding energizes the bigger one that is itself resonated with its own capacitor. Thank you! I could try and build one like this just to try it

[Altra]

I suppose that winding two wires at once is needed in order to have both coils on the same plane. Anyway, i took a look at the designs you suggested and they are pretty complex, with multiple tapped coils. Not really want to dive into that hahahaha. Thank you very much, I hope I will have time to go deeper into the topic.

No need to wind two coils at the same time. For a center tapped coil for instance, wind 30 turns and stop make a a short loop away from the main bundle. Bring the wire back to where you stopped and wind 30 turns more. Now you have a 60 turn coil with a center tap at 30 turns. The patent will be the same but you might wind like 10 turns, make loop(tap) and wind 50 turns on top.. This would be a 60 turn coil with a tap at 10 turns

[pito]

wire 0.6 mm, 8kHz coil diameter 22 cm.

[dbanner]

coils should be bifilar wound to ensure mutually coupled coils, (both sides are well balanced with same inductance and high coupling coefficient). Otherwise it won't work very well.

The fisher 1260x used such a coil,(as well as Nautilus and Aquasound. Don't be confused with all those windings, they are just the feedback coils for a concentric coplanar IB coil arrangement

You could wind a DD coil type with just bifilar and centre tap ( no feedback windings required for cancellation). Drive it with a circuit similar to 1260x TX circuit

[dbanner]

aquasound schematic depicts a slightly different arrangement, this might be more akin to the "autotransformer" description. I suspect such a coil would have to be wound with four wire "quad-filar" and the start/finish of each wire connected in the appropriate manner as per the schematic of the coil. No feeback windings would be required as there is a feedback system with potentiometers to achieve induction balance. That would be my guess.

[Altra]

The coil part of the aqua sound schematic is incorrect also the 2n2222 driving the coil should be a 2n2907. See the Nautilus 2B schematic

[nejdet]

Check out the Nexus Generator
https://www.geotech1.com/forums/foru...64-md-nexus

[Skippy]

Quote:"No need to wind two coils at the same time. For a center tapped coil for instance, wind 30 turns and stop make a a short loop away from the main bundle. Bring the wire back to where you stopped and wind 30 turns more. Now you have a 60 turn coil with a center tap at 30 turns"

This is poor advice. Winding bifilar is the easiest way to wind such a coil, not a "harder way" , and it guarantees identical performance for each half of the wind, with the centre-tap truly central.

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If the OP was wanting a higher step-up ratio, he could wind the TX tri-filar ( three wires at once ) to obtain a 3:1 step-up voltage ratio.
Edit: it would actually be better to wind this quadri-filar, and then parallel-up two of the windings to make the driven winding.

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I recall Nok-Mak used a T2-like coil on their Racer machines, and maybe later models, Impact?. The electronics schematic is 'out there' somewhere, I have seen it posted on here, but didn't save it. I will try and scour the Forum to find it.

[pechkata]

Here is a schematic...

[pechkata]

And this schematic tells us how to approach acceptance...

[Pep_T]

Thank you all for all the material you provided me. I have only one question tho about some of the schematic you posted: some of them have a coil in parallel to the one with central tap. I assume it works as a secondary? Like there are both autotrnasformer and "proper" transformer in a single coil?