[Lowfer] Coil question???

[Mitch Powell]

> 
> Hmm, 11 "pipes" to weave around and holding it all together. Nice. I
> calc about 335 feet of wire was used.
> 
> Mind telling how you held the wire to weave that coil? Was the coil
> turned about or did you, the winder, turn about the coil, feeding the
> wire?
> 
> Was stranded wire used? Were the turns pulled tight or allowed some
> slack around the tubes?

Hi Peter:
I had wound a large coil, used for 136 kHz work, following Bill Bowers
techniques: i.e. 10 inch plastic pipe, 1 inch foam spacers, and an L/D ratio
of 2.5.  Q was great, and had lots of inductance. Worked well for year.

However, the layout that Dex uses appealed to me - so went to Home Depot,
picked up the plywood and several pieces of 3/4" white PVC.
Cut two 24" square pieces of plywood, then drilled 11 holes in 18" diameter
circle (drilled both at same time so would match -hi !).
Pipes were cut to 18" length, and inserted in bottom plywood - used silicon
caulking. (Dex drilled holes for tight fit).
Now I had 11 vertical pipes and wanted to weave the wire - 14 gauge, solid
copper, plastic cover - for household wiring.

Two immediate problems:
1 - can't put top piece of plywood on pipes - and wind this size wire.
2 - without top support, the pipes bent and moved all over the place and
wouldn't maintain spacing and remain vertical.

Solution: Cut 4 corner posts (using 2x2 pine) and mounted these on plywood.
Had some 3/4 inch styrofoam sheets - and cut a piece 24" square.
Drilled 11 holes - and notched out the corners to fit tightly on the corner
posts. Slid this flat sheet down the pipes about half way. Now the pipes
stayed vertical, and I had a support for the winding - without having a top
piece of plywood interfering with my coil winding.
Drill a small (wire sized (1/8" ?) hole in one pipe to attach the first
turn.


I then slipped the coil of wire on a piece of pipe, and mounted the pipe
with wire horizontally, and OVERHEAD. I could now pull the wire vertically
down from the ceiling. Sat the "coil form" on my Workmate underneath the
wire and started laying the wire around the pipes. Went very quickly, and
had the 70 turns wound in a few minutes. I had to put a wedge on the coil of
wire to keep some pressure on it as I unwound.....otherwise it would run
away and supply faster than I was able to "lay" the inductor.

When I was finished - I checked the Q and inductance - found I had 2.7 mH
and Q of 420. I removed a few turns, got 2.4 mH, then wound a simple coil of
one layer with no spacing on the bottom section of a Home Depot 5 gallon
paint bucket. This was 30 turns, approx 10 inch diameter and fit nicely
inside the bigger coil.

Now I can place the plywood on top, screwing down to the corner posts.
I also could remove the styrofoam sheet and/or slide the main coil up and
down - and do some cosmetic changes - and vary the inductance a bit.

Well Peter - that was a bit of a description, and I only share it with you,
without any expectation you will do it in the same manner. However, every
little bit helps.

By the way - There was an excellent article in QEX. Sept/Oct 2001, pages
26-32. The article was on "The Art of Making and Measuring LF coils". It
confirms everything about L/D and gives some interesting ideas for making
very nice Hi-Q coils.  Adding that to the Bill Bowers article, and you can
come up with some excellent coils that have been well proven.

I can copy the Bowers article if you do not have it. It's calculations
are very simple (three steps) and as I said, I came within ONE turn of the
inductance I required.

73
Mitch VE3OT