Bill Janssen wrote:

How about making an Air Core Toroid. That can be made using a wax core.
Then after winding it,
some QDope or something in strips to hold the windings and then melting
the wax. Or maybe a foam
plastic core.

Bill K7NOM


There was a manufacturer in the 20s that used a coil like that. Thorola
- they called them donut coils. Looks like they just wound them on a
small form, maybe 1 inch, and then slid it off and bent it around
afterwards into the form of a donut.

Never heard any comment yeah or nay about their efficacy.

-Bill M