[RFI] Ferrite Beads

[Tom Rauch]

> Third, as you do multiple turns, the stray capacitance
shorts the choke at
> higher frequencies, so a multi-turn choke optimized for
160 or 80 will
> probably be a lot less effective on 15 meters and above.

I agree with that.

http://www.w8ji.com/toroid_balun_winding.htm

I'll have to redo that page someday with better pictures,
and add some other beads. 1" 44 mix beads with 4-5 turns
have an impedance peak around 7 MHz or so, and are still
good at 30. Not at the peak, but way better than a single
pass through would be. But by the time you reached 160 or 80
on the peak, 15 up should be getting bad.

The problem with car wiring is you can't use multiple turns.
By the way, you can de-Q a bead. Add a secondary with a
resistor across it. You can even tune it.

To see what I did to cure a Ford PSD, look at:
http://www.w8ji.com/rf_noise_powerstroke_diesel.htm

Sometimes finding a sweet spot for grounding helps. There
isn't a single bead in my truck wiring. Just grounding two
points cured it all.

73 Tom