On Tue,6/13/2017 8:33 AM, Kimberly Elmore wrote:
I have a naive question: I've come into some FT-240 type 31 toroids. I'd like
to make them into common mode chokes. I've read about the types that use 6-12
large toriods with 4-5 turns of coax as common mode chokes. Would 10 bifilar
turns of 16 ga magnet wire (twisted to a couple of turns per inch so as to keep
the two wires together and simplify he winding) through a single FT-240 work
about as well? If not, why not?
Depending on the use, just as well or almost as well. See (study)
k9yc.com/RFI-Ham.pdf and http://k9yc.com/KillingReceiveNoise.pdf
which shows a bifilar-wound choke using #12 THHN or #12 magnet wire
connected as a 2-wire transmission line. #16 is small if you're running
high power, otherwise it's fine. Conductor gauge and spacing affects Zo
of that 2-wire line. #12 and #14 magnet wire closely spaced results in
about 50 ohms, THHN about 85-95 ohms. Jerry Sevick, W2FMI, published the
first data I've seen on this, and I've confirmed those numbers in my lab
to reasonable accuracy.
Note that the chokes with many cores stacked are for high power. More
turns on fewer cores are fine for low(er) power.
73, Jim K9YC
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