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Re: [TowerTalk] Coax soldering

To: "" <>
Subject: Re: [TowerTalk] Coax soldering
From: "Jim Brown" <>
Date: Wed, 21 Oct 2009 17:41:28 -0700
List-post: <">>
On Wed, 21 Oct 2009 17:05:43 -0400, Jeff Carter wrote:

>Here's a good point of departure.  It's got a chart of the different
>toroids you want for different power levels, and a really good diagram
>of the windings required.


I don't agree at all that this is a useful reference. First, it does NOT 
specify the ferrite material type or dimensions, which the is most 
important specification.  

Assuming that the "open wire line" in question has impedance on the order 
of several hundred ohms, what is needed for the application is a matching 
transformer of some sort with an impedance ratio of 4:1 or higher. In 
other owrds, a so-called "voltage balun" or "transmission line transformer 
of some sort. I suspect you'll find winding instructions in the ARRL 
Handbook. For a ferrite material, the only good choice in the US is Fair-
Rite Products #61, which is widely available as a 2.4-inch o.d. toroid. 
This is often called FT240-61 by vendors who mark them up at 4X cost and 
sell them to hams. 


Jim Brown K9YC


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