[Amps] 50ohm:200ohm toroidal transformer

[gdaught6@stanford.edu]

Hi all,

I'm trying to build a 50:200 ohm broadband transformer for the input 
of a tetrode amplifier.  Sevick's book and Measures' website give 
instructions for such a 2.4 inch unun.  Sevick says it can handle 
over a kW: I only need a 100W job.  The ARRL handbook says a 1.5 inch 
version will handle over 100W.  Does anyone have a "recipe" I could 
follow to make such a thing?  Requirements are:

a) 50 Ohms to 200 Ohms
b) 3-30MHz
c) low loss (I don't want it heating up and self-destructing)

What core material and what size should I use?  What is the best 
place to get one (or two) of the cores? What wire and how many turns 
should I use?

I readily confess that I'm woefully knowledge-and-understanding-
deprived in this area!

Thanks in advance for any help!


73,George T. Daughters, K6GT