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

[Bry Carling AF4K]

Good discussion about ferrite materials.

I noticed the same with LDG Baluns. They use a TINY amount of ferrite for a 100 watt balun 
and the thing overheated the first time I used it and melted the case. No more cheap Chokes 
and baluns here. I switched to the higher priced larger QRO baluns from another 
manufacturer.

On 27 Apr 2015 at 9:31, Jim Brown wrote:

> 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
> 
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