> I think 43 was the default choice some years ago as it
covers all the bands
> from 160 - 10 meters (and maybe 6 if you're not too
picky). However, in the
> range you mentioned, (.1 - 7) 75 & 73 are surely better
choices based on the
> permeability curves.
73 material is a good choice up to 30MHz and higher. 43 into
the hundreds of MHz. For example I use 73 materials in
feedback transformers in HF amplifiers in applications where
they have to maintain voltage or current and phase angle
over wide frequency ranges.
Loss on lowbands isn't much of an issue, and systems can
tolerate a fair amount of impedance mismatch without ill
effect. The major issue for most people is probably how
difficult these transformers are to construct and how immune
they are to lightning. The 73 material binocular cores
manufactured by Fair-rite products (resold by Amidon) allow
healthy wire sizes to be used.You also can get some
thickness in the wire insulation reducing chances of
punch-through.
73 Tom
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