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.
>http://www.pd7bz.com/radioprogs/manuals/balun_transformer.htm
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.
73,
Jim Brown K9YC
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