Owen Duffy wrote:

Hams have a affinity for powdered iron cores in RF applications, mislead
by the thought that low loss material naturally produces a better
solution. Thing is that it is a huge leap from low loss *material* to a
low loss *solution*.

. . .

Would such a balun wound on a powdered iron core work better? Probably
not. I say probably because I have been unable to find manufacturer's
loss data for powdered iron materials above about 5MHz. The probability
is that a powdered iron core would yeild a balun with a choking
impedance that is lower and more inductive than resistive and may likely
be *more* lossy. (I have a prospective project to measure a couple of
powdered iron cores at 6m to further explore this, but they will not be
lab grade measurements.)

. . .

Like ferrites, powdered irons come with a wide range of characteristics.
Micrometals (http://micrometals.com) makes the popular -2 (red), -6
(yellow), and other cores which are very suitable for high-Q inductors
at HF, as well as lower frequency mixes. I have a book of "Q curves"
they published which characterizes a number of inductors to fairly high
frequencies. But for most of my work I've simply wound inductors and
measured their Qs with a simple home made Q meter. I use -6 and to a
lesser extent -2 cores for inductors in nearly all HF filter and
matching applications. I've used lower frequency powdered iron cores for
RF chokes. They behave a lot like low frequency ferrites, but are
characterized by tolerance of very high flux densities. I'm sure that
some low frequency powdered iron cores would be fine for baluns and
broad band transformers, but they're not nearly as available as ferrites
and high frequency powdered iron cores.

I highly recommend that anyone anticipating using ferrite or powdered
iron cores invest in an "antenna analyzer". It allows a very quick and
easy characterization of cores at the frequencies of interest.

Roy Lewallen, W7EL