Topband: Wideband x-former...

[Jim Brown]

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