[TowerTalk] [Bulk] Re: G5RV vs 40M dipole

[Jim Brown]

On Sun,4/26/2015 12:08 PM, Kelly Taylor wrote:
> If the choke bead is getting too hot, it doesn't mean you shouldn't use a
> choke. It means the choking impedance isn't high enough. Either the beads
> aren't the proper ferrite material or there aren't enough of them. With many
> commercial bead chokes, it's sometimes a combination of both errors.

The ONLY ferrite material I know of that works for a string of beads 
choke on the HF bands is Fair-Rite #73. It is the material that W2DU 
chose for his common mode chokes  that he called "current baluns." The 
#73 material is resistive in the HF spectrum, which satisfies one of the 
requirements of an effective choke. The other requirement is that the 
resistive impedance must be high enough to suppress current enough. 
Overheating means that there is not enough resistance.

> If anything, the heat is proof a choke is required, because if that energy
> wasn't making the bead choke hot, it would be on the outside of the
> feedline.

Exactly right.

Remember -- any inductance in a choke resonates with the capacitance of 
a feedline that is shorter than a quarter wave, or some multiple that is 
capacitive. To be effective in all situations, the choke must be RESISTIVE.

73, Jim K9YC