Re: transformerless TCs/ would a variometer be useful?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
>  This sounds very much like the antenna tuner that is inside an "old"
> arc-5 military unit i got off of ebay. It uses a coil wound around a
> ceramic tube (1.5" dia.) and then another coil inside the tube, this is
> a flat coil that is rotated 360 degrees within the tube. It's been
> awhile since i've really looked at it, but i could send a pic or send a
> couple to hot-streamer if anyone is interested? I always thought that
> this would be a great primary tuner if scaled too the needs of any coil?
> Take care.
> Marc M.
> 
> > make two coils, place them over a thick insulating plate (as I did in my
> > setup), and move one of them to tune.
> >
> > Antonio Carlos M. de Queiroz

	Antonio's scheme is a lot easier to build, at least if I understand
what he's saying about the relative position of the coils.  By sliding
one within the other (connected in series AIDING, of course) you can
vary the inductance quite smoothly.  If you're only going to tune it
occasionally this is the best solution.  The conventional
rotating-winding variometer is used where the adjustments are frequent. 
I've designed and built a number of them; they work fine but require
that the inner coil diameter be such that it can rotate without
interference.  That restricts what can be done, at least if ordinary
cylinderical coils are used.  "In the good old days" the outer and inner
windings were ball-shaped (sectors of spheres), which gives a little
better performance at the expense of a lot more trouble to build.

Ed