[Amps] construct ferrite "line isolator"

[Vic K2VCO]

Two common misconceptions about toroids and rfi:

1) 'Ferrite' and powdered iron are very different materials although lots of guys 
incorrectly just say 'ferrite'. The important thing for our purposes is that ferrite 
increases the resistive loss of a conductor that passes through it as well as the 
inductance. Powdered iron has much less loss in the frequency range that a particular 
material is designed for. Therefore, ferrite is most useful for suppression of RFI caused 
by currents on the outside of coax, etc., where powdered iron is good for tuned circuits 
where you want to increase inductance with minimum loss.

2) Putting a single ferrite bead on a cable, like you see on computer monitor cables, has 
very little effect at HF. Either you need a lot of beads (choke baluns are commonly made 
with 25 or 50 beads) or you need a toroid large enough to wind multiple turns of cable 
through.

I know you technical guys know this, but I don't know how many times someone tells me "I 
put a bead on the cable but it had no effect."
-- 
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/