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
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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