Topband: best core material?

[James Rodenkirch <rodenkirch_llc@msn.com>]

I have a schematic for a delta shaped loop that shows I'll need an 18:1 
transformer to transform the 950 ohms of the antenna to 50 ohms (feeding it 
with 50 ohm coax).
 
One transformer diagram shows an FT-140-43 core being used.
 
BUT, looking over some of Tom's, W8JI, write-ups, I see where he uses 73 
material instead.
 
I see where 77 material replaced 73 material so -- is an FT-140-77 the mo betta 
way to go?  
 
 
Thanks, in advance, for any advice/info.  Jim Rodenkirch K9JWV
 
 
                                          
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Topband Reflector