[Amps] Line Isolators for RF feedback

[Ian White, G3SEK]

Following-up my previous message...

>Over its "wideband" region, a ferrite bead becomes increasingly 
>resistive as well as inductive. The resistive losses in each bead will 
>be I-squared*R and these will of course heat up the bead.
>
>However, the "I" that we're talking about is the surface current on the 
>coax, that the balun is trying to suppress. If you use enough of the 
>right beads, you will create so much R in series with the current path 
>that I will be reduced to a very low value, so the heating effect in 
>each bead will be very small.
>
>The only times you can expect serious heating in a bead balun are if at 
>least two of the following factors apply:
>1. Defective balun (not enough beads, wrong core material, broken 
>beads, incorrect construction)
>2. Diabolically unbalanced antenna (so fix the antenna already)
>3. High power.
>

There is good information, including estimates of power dissipation for 
a range of commercial bead baluns, at:
http://www.w8ji.com/Baluns/balun_test.htm


-- 
73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek