Jim Brown wrote:
> 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
Jim is exactly right. I use a stack of three 2.4 inch Fair-Rite #61 for
the 450 ohm balanced to 50 ohm balanced transformers I have at each
end of my 850 foot long open wire line. They work very well.
(There are also, of course, 50 ohm to 50 ohm baluns at each end.)
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