On 10/26/11 5:21 AM, Bill Jackson wrote:
> Good Morning,
> I need to rewind one of the linear loading coils on a Cushcraft 402-CD that
> fried by lightning. According to a web article I read, the coil consists of
> turns of #12 AWG magnet wire, close spaced, on a 3/4" fiberglass rod. I
> already have the wire on hand.
> My question is directed to those of you who build your own antennas. Is there
> any technique or home brew aide(s) that will assist in getting this coil wound
> tightly with no spacing between the turns? I seem to recall seeing an article
> many moons ago that talked about using a paint stirring stick with a hole
> drilled in the end to hold the wire while you wind it around the core. #12
> is pretty stiff for a 3/4" form and I want to make it look as good as the
> factory original.
First, make sure your wire is fully annealed. If it's been work
hardened at all (as by being coiled and straightened before, or worse,
it's been stretched straight under tension), it will be a lot tougher.
One trick is to wind it on something else with a closer pitch than you
want, so it's a spring that wants to stay closed. Then you slip it over
your form and let it "spring closed" on the form. What you want is three
grooved pulleys spaced appropriately, for instance.
But, having wound lots of close spaced coils, what it really comes down
to is appropriate glue, and a fair amount of tension in the winding
process: you don't want the turns loosening up when it gets warm and the
wire expands; it should be in tension on the form (so solid rod is a
good idea, it won't crush). Wind it tight, hold it under tension, coat
it with something tough, and you're done. Dolph's AC43 is a popular
winding coating for high voltage/high temperature applications. Various
2 part epoxy and polyurethane coatings also work well.
At the factory, I'll bet they have a jig that clamps one or both ends of
the rod so they can put a fair amount of tension on the wire as it gets
wound to keep it snug.
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