On Mon, 30 Mar 2009 19:38:05 -0700, Richard (Rick) Karlquist
wrote:
>Even easier. You can simply get a big 43 matl toroid and wind an
>autotransformer on it.
Hang on a minute. The original post said "can handle some power,"
but didn't say what frequency. #43 "will handle some power" on
160M and 80M, but it will begin making more and more heat as
frequency is increased above 40M.
The best answer to the original question is to study the materials
pages in the Fair-Rite catalog (it's online), and look for the
curves that show u' and u'' versus frequency. u' describes
inductance, u'' describes resistance. You want a material that has
fairly high u' and fairly low u'' at the frequency(ies) where you
want to use it.
Fair-Rite #61 and #67 are suitable for HF transformers that can
"handle some power." Read the descriptions on the first link, then
study the curves on the three remaining links (top left curve on
each page). Pay special attention to the frequency at which u''
begins to rise. That's when the material will begin to burn power.
http://www.fair-rite.com/newfair/materials.htm
http://www.fair-rite.com/newfair/materials61.htm
http://www.fair-rite.com/newfair/materials67.htm
http://www.fair-rite.com/newfair/materials43.htm
73,
Jim Brown K9YC
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