John Popelish wrote:
. . .
I appreciate you taking the time and effort to try to straighten me out
on this, but if there is no magnetic lines broken (whatever that means)
why use a magnetic core? Why wouldn't disks of carbon work just as
well. They are certainly resistive.

But resistive impedance isn't the only characteristic of ferrite. Disks
of carbon won't work because they have a relative permeability of one.

Fair-Rite type 73 ferrite has a Q of 1 (R = X) at about 3 MHz, and is
essentially resistive above that; it's a "low frequency" ferrite. But
its relative permeability is 700 at 10 MHz and 70 at 100 MHz. (Note that
the permeability is a complex quantity, and that the permeability is
mostly imaginary, hence the impedance resistive, at the higher
frequencies.) Carbon has a relative permeability of one at all
frequencies. The impedance of a type 73 ferrite core picked at random
from the Fair-Rite data shows an impedance of 23 ohms at 3 MHz, 37 at
10, 51 at 100, and 49 at 200 MHz. Try making a carbon disk that'll give
you that impedance. And if you make your baluns with multiple turns on a
single core as I do, you'll have much poorer coupling between turns on a
carbon core, than on ferrite.

You'll learn a lot by reading the information in the Fair-Rite catalog,
available at their web site. Good, professionally written information on
EMI suppression is useful also. But I don't recommend looking to amateur
publications and web sites for information on ferrites -- too many
people share the same misconceptions you do, and pass them along without
really understanding how transformers work and the properties of
ferrites. Actually, a large number of engineers share those
misconceptions, too. It's often one of the first things I have to
explain to the engineers in my consulting work.

Roy Lewallen, W7EL