>>>...The 2 inch long ferrite clamp on "beads" sold by radio shack are about
>$3 or $4 each. I used about 25 of them on the Stereo and 10 more on the
>leads from the computer to mouse and keyboard and monitor." <<
>These ferrites are usually not very effective at low frequencies. Just as
a
>rule of thumb, I'd count on 50 to 100 ohms at 100 MHz and near ZERO ohms at
>10 MHz for one pass of wire through the core.
Actually, they are moderately effective at lower HF, *IF* you use enough of
them. A good rule of thumb is that you need to use the same number of them
as would be used to make a bead balun. That translates roughly to 0.5 per
meter, as a minimum, ie - about 20 to make a 40 meter choke. As you later
point out, at $4 each, that gets pretty expensive. An FT-240 size ferrite,
(use #75 or -J material for low HF, #43 for upper HF) is a LOT less
expensive.
73 from ARRL HQ,
Ed Hare, W1RFI
ARRL Lab
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