DD Coil Electronic Balancing with Compensation Coil and Trimpot

[Byko]

A balance-tuning coil for the RX circuit can be placed within the TX coil area. It consists of two series-connected compensation windings, each of 2–4 turns of wire of the same gauge as the RX coil. The center tap is connected to the cold end of the RX coil. The free ends of the two compensation windings are connected to the outer terminals of a 50–100 Ω tuning potentiometer, and the wiper is connected to ground, as shown in the attached figure. This arrangement was successfully tested on a DD coil prototype.

[Carl-NC]

I like that. I'm working on something similar except for electronic nulling, using a digital pot. That way final null can be achieved after the coil is sealed, or after a few years where the null has drifted. The smallest value dpot I can reasonably find is 2kΩ and that is too big to apply directly to the windings because of thermal noise. Otherwise, I'm using a bucking coil on the RX side just like you have done, and combining after a very modest amplifier gain.

[Altra]

Good work Byko! Thanks for posting...

[pito]

Good work Byko! Thanks for posting...

why you say good, it is VERY GOOD, the best and simplest solution for balancing the coil, make a access to the potentiometer using the cap

[pito]

test

[pito]

[pito]

https://www.youtube.com/shorts/BlFnZXQ7ak4 I am using the buttons, this is Rx amp output

[Altra]

It's very good, because it is simple and uses passive components.
I did mine here and could add digi-pots if I wanted to.

https://www.youtube.com/watch?v=a8NI_632VIA

[Byko]

Carl, about a year ago I purchased a kit with 3386P potentiometers on AliExpress. I like this type because it has a small lever that allows you to adjust it without a screwdriver.