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Re: Topband: FERRITE BEADS

To: Topband@contesting.com
Subject: Re: Topband: FERRITE BEADS
From: "CHARLES HUTTON" <charlesh3@msn.com>
Date: Fri, 19 Dec 2003 20:07:04 +0000
List-post: <mailto:topband@contesting.com>
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@contesting.com>
Reply-To: Tom Rauch <w8ji@contesting.com>
To: "Dan" <w0vd@sofnet.com>, <Topband@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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