Jerry,
I picked up a copy of "Building and Using Baluns and Ununs" by Jerry Sevik
at the Dayton Hamvention. This is an interesting, but practical
reference. You might also check out their web site. They sell kits,
cores, and practically every concievable balun and unun you might imagine!
No connection to them, just a happy customer...
http://www.cwsbytemark.com
73,
Steve
aa8af