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From: N1BUG <paul@n1bug.com>
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Date: Wed, 21 Mar 2018 06:54:21 -0400
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Subject: Re: LF: Re: [rsgb_lf_group] Idea for tuned inductor
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> The pot core with adjustable air gap is a nice idea, but at high power
> I think I'd need a huge core to avoid saturation. Elegant though :)

I can see the headline now... "Exploding Ferrite Damages Property,
Awakens Neighbors" ;-)

It is an interesting idea that would seem fun to play with if I
happen to run across a big pot core.

Chris, that Russian goniometer is an interesting looking device.
Nice find.

On the subject of variometers, I made mine a little different. It
uses traditional air core coils but the inner one moves up and down
rather than rotating. Originally it was adjusted manually:

http://www.n1bug.com/lfmf/2200m-coil-vario.jpg

But has since been motorized:

http://www.n1bug.com/lfmf/2200coil.jpg

Tuning is very slow and precise. In hindsight the 5 RPM motor is
probably a bit too slow. 10 to 15 RPM would have sufficed nicely. I
may swap out the motor if I can find a faster one with the same
shaft and mounting hole pattern.

I don't know if this has any advantages over the typical rotating
coil arrangement. It does have one disadvantage in that the total
range of adjustment is far less. I have since added more taps to the
outer coil at 1, 2 and 3 turns from the low end to help set the
tuning range.

73,
Paul N1BUG