Topband: FERRITE BEADS

[CHARLES HUTTON]

My answer for 160 is to build a special little box that has as many turns of 
RG-174 or RG-189 as possible on the biggest ferrite toroid I can find, 
usually using J material as broadcast stations are my problem.

I don't think you can really get enough Z out of a handful of beads to come 
close to solving the problem. In some applications where you are interested 
in a low Z path to ground (like the coax run between a Beverage transformer 
and the radio), the voltage divider effect between the ground resistance 
(let's say 100 Ohms) and the choke means that you're going to want a lot of 
Z in the choke. I aim for at least 10K and hope for 100K. That's a mountain 
of beads.

Chuck




>From: "Tom Rauch" <w8ji at contesting.com>
>Reply-To: Tom Rauch <w8ji at contesting.com>
>To: "Dan" <w0vd at sofnet.com>, <Topband at contesting.com>
>Subject: Re: Topband: FERRITE BEADS
>Date: Fri, 19 Dec 2003 06:20:40 -0500
>
> > How many of these will I need to put over the coax to make an effective
> > balun?
>
>It depends on the balun impedance your exact application requires, but the
>answer is probably more than you would every care to purchase!
>
>You need to be up around a 65 material at high power high stress
>applications, or 73 Materials with modest stress on the balun.
>
>You also need multiple turns through one core window rather than a string 
>of
>beads, otherwise the number of cores required on 160 would be pretty high.
>An air core choke is a cheap alternative.
>
> > Another question on the same line.
> > Several years ago I saw either in a mag or handbook where a current 
>balun
> > was made out of steel wool placed over the coax. The steel wool was
> > compressed inside a plastic tube with the coax run through the middle.
>
>I called the ARRL's attention to the fact the steel wool does not work at
>all. They tested and confirmed it, and removed  that info from the 
>Handbook.
>I hope it is still gone. I don't think anyone should laugh at that. It
>really isn't a laughing matter when a book like the Handbook or QST gives
>useless information to people trying to work on stuff.
>
>73 Tom
>
>
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