[ARC5] Coils and the winding thereof

[Kenneth G. Gordon]

Michael:

In the small transmitter you are thinking of building, several 
layers (for strength) of varnished paper, or those cardboard 
cylinders inside toilet-paper rolls (varnished) make perfectly 
good coil forms. 

Although they are somewhat "delicate", there is so little actual 
material there that the resulting coils are almost "air wound".

You could also simply use stiff, solid wire, like #12 or #10, wind 
the coil on a dowel, then take it off the dowel and use it "air 
wound".

If you want a plug-in coil, use an old tube-base with the toilet-
paper cylinder glued to it....or wind your own cylinder out of 
several layers of varnished stiff paper around the chosen tube 
base.

Certain sizes of PVC tubing fit tightly around certain tube-bases, 
but you should probably check the PVC to make sure it is not 
lossy at RF. Simply stick it in the microwave for a few minutes. 
If it gets hot, it is lossy at RF. If it doesn't, then it is fine.

Then use that Epoxy glue specifically made for gluing plastic.

The purpose of boiling wooden coil formers in parafin was to 1) 
drive as much moisture out of the wood as possible, and 2) 
subsquently prevent the wood from picking up moisture from 
the air.

I never felt the need for it, but did varnish the wood when I used 
that material.

Ken W7EKB