Actually it is permeability tuning in reverse: inserting the slug decreases
inductance, but the net result is the same- moving the core changes the
inductance. The physical mechanism is different: in magnetic tuning the core
actually increase the permittivity of the magnetic circuit and allows a
higher level of magnetic flux to occur for a given inductor current.
With nonmagnetic core material the mechanism is based on the occurrence of
Foucault currents in the core that substract from the initial permittivity,
thus reducing the inductance.
Both are viable, but the non magnetic core is lower loss at the higher and
microwave frequencies. You can't use magnetic cores there.
Alex Z5KS
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Chris Wilson
Sent: Thursday, January 16, 2014 12:23 PM
To: amps@contesting.com
Subject: Re: [Amps] Permeability tuned tuning coils, with taps?
Thursday, January 16, 2014, 9:50:16 AM, you wrote:
> Somewhere in the seventies, in the ARRL handbook, there appeared a 6
> meter amplifier tuned variometer style with a one turn shorted coil,
> rotating in the stationary tank coil. It wasn't very wideband as I can
> recall, but it worked.
> It seems to me, Chris, that you won't have any qualms about
> plagiarism: it was definitely more than 20 years back!
> Alex 4Z5KS
I have an older ARRL Handbook showing a coil that is compressed and allowed
to re-expand via an internal threaded rod and two (Teflon?) plates at either
end. I have a Russian R-140 tetrode amp that uses variometers, with complex
auto control. Is "permeability tuning" the correct description of a coil
tuned with a none magnetic material slug? Or is that getting pedantic?
Thanks for the replies.
--
Best regards,
Chris mailto:chris@chriswilson.tv
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