Re: Continuously variable primary

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "S&JY" <youngsters@xxxxxxxxxxxxxxx>

There is another way that could be easier to construct.  Just  use a normal
primary, with the inductance set 10% or so lower than what is needed.  Then
put in series an off-axis variable inductor that is not magnetically coupled
to the primary.  One might think the off-axis inductance would noticibly
decrease overall coil efficiency, but it doesn't.  Just keep it away from
large metal things, the same as you would for a primary.

The variable inductor can be a beefy roller coil, such as some hams use in
antenna tuners, for example.  Or it can be two small opposing spirals that
you can move closer or farther from each other with an insulating rod, or a
cheap electric screwdriver turning a threaded rod (poor man's linear motor).
I experimented with the latter, but decided it's not worth the hassle.

--Steve Y.


>  > A far simpler approach would be to construct >> two
>  > conventional flat primary coils, joined in the center with a
>  > short >> length of flexible cable, and have a mechanism to
>  > vary the separation >> between them. This will vary the
>  > mutual inductance, and consequently, >> the net inductance
>  > of the two coils in series.