Re: Variable Inductance

Richard Quick wrote:

> In the four inch diameter tubing I believe there is ABS thin wall 
> and PVC thin wall which telescope fairly neatly. I had thought about
> getting a 30 pound spool of bailing wire and cutting the wire into
> yard long sections. The cut wire could be layed out on some waxed
> paper and coated with polyurethane or other sealer. Once dry the
> lengths of cut wire could be tightly bundled, wrapped with a few 
> spots with plastic friction tape to hold it, and fitted inside the 
> smaller plastic tube. The cylinder core would then be potted with 
> epoxy to prevent vibration. 
> Around the larger plastic tube a coil four inches in diameter and
> three feet long could be wound with some #6 wire. The coil would 
> probably need to be wound with bared stranded or solid enamel 
> covered copper, then coated with enough epoxy to pot the winding. 
> The core would be drilled and tapped at one end for a mounting 
> bolt, then fitted inside of the coil and mounted in a simple
> wooden frame. A crank handle and draw screw would be fitted to the 
> mounting bolt on the core, the coil would remain stationary. By
> cranking the handle and drawing the core in and out of the coil,
> the inductance would be varied.

In reading through the fidonet archives you sent me when I first 
contacted this group, you had mentioned home brew ideas for a
variable inductor.  Thinking about how I would do it, I came
up with the same ideas you described above. It would help to have 
large graduations marked on the inner core and I had thought about
a reversible motor to run the core in and out "on the fly".  
(maybe an old garage door opener).

Medium duty arc welders don't cost too much used.  ($100 or less).
I've got an old Montgomery Ward model that still works great after
15 years.  Hopefully it will work well with my coil.

I'm going to have to be leaving the group here for a while
as I was just notified I have to go to Egypt on a 90 day TDY,
leaving here in ten days.  (Real kind of 'em, eh?)

I've come really close to finishing up my 6" coil.  I've completed
two poly caps, two cylindrical spark gaps, the secondary, and
a toroid, but it doesn't look like I'm going to get much further
until after Christmas.

BTW, is anybody keeping an archive of the daily banter here?
It would be a shame to miss out on three months worth.  
Hopefully I can catch up when I get back.

-Mike McCarty

[ I do save all the past postings by date, so you could get them when
  you get back.  -- Chip ]