I guess I'm using the term "beads" a bit figuratively taking into
account toroids big enough to pass a coax connector on RG-213. For HF
choking they need an initial permeability of a few hundred to 1200 or
so. For a transformer that permeability for HF would be 50 or 125. Its
really hard to put multiple turns of RG-213 through any size of toroid.
Yes on the basis of the least cost of ferrite, a chunk of teflon coax
winds on ONE large toroid to make a decent choke, but that teflon coax
gets warm at 1200 watts or more.
Snap on RFI toroids are in the same region of sizes, but the potential
for a lowered effective permeability due to the airgap at assembly is a
significant problem.
73, Jerry, K0CQ
On 8/6/2010 1:15 PM, Jim Brown K9YC wrote:
> On Fri, 06 Aug 2010 12:43:30 -0500, Dr. Gerald N. Johnson wrote:
>
>> That depends a great deal on the ferrite mix. There are beads suitable
>> for HF
>
> The only beads I know of that are suitable for HF are the tiny beads that
> W2DU found 30 years ago for his chokes. They only fit miniature coax, and
> it takes HUNDREDS of them to make a choke that still doesn't work as well
> as the multi-turn I've described. Those made with fewer beads are less
> effective AND they can be blown up with high power.
>
> 73, Jim Brown K9YC
>
>
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