Re: LF: Multi-layer loading coils

[DL4YHF@aol.com]

Hello Ha-Jo and LF group,


> It seems that the metal of the inner coil increases the loss 
> of the outer coil (and possibly vice versa).

Exactly that's what I found in own experiments.

By "forcing" the magnetic field through any kind of metal, you increase the losses. 
For the same reason, long coils shouldn't be wound too closely, which is especially true when using enameled copper wire. Some of the mag field lines don't run through the full length of the coil, but 'escape' to the  sides. Forcing them through the very thin gap between the copper seems to cause additional loss. Using a calculation program for single-layer coils (like COILS.EXE from an old ARRL handbook) you can see the effect, and it can be verified in practice. 

73,  Wolf   DL4YHF.