Topband: Fabricated common mode chokes - Sourcing

[Jim Brown]

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