A year or two ago, based on the experience of some hams in the UK who found Fair-Rite cores either impossible to obtain or very expensive, I did some more experimental work that resulted in designs for transmitting chokes that can be wound on a single #31 core, be very effective from 80-10M, and handle at least 500W with antennas that have reasonably good balance. If the antenna is well balanced the choke can handle legal power.
The new designs use bifilar windings -- that is, two conductors taped together and wound around the core that function as a parallel wire transmission line in place of coax. An alternative design uses more turns and covers 160-15M. These designs were added to my RFI tutorial last summer (June 2010). The best of these designs use ordinary "house wire", known in North America as THHN. The tutorial is http://audiosystemsgroup.com/RFI-Ham.pdf 73, Jim Brown K9YC _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK