>I have 850 feet of open wire line to my 160 vertical. There
>are numerous photos of it on my web site at
>http://www.n6rk.com/openwire.html.
>It is 4 AWG stranded aluminum XHHW wire, spaced 5 inches. At
>both ends there are baluns to convert from unbalanced 50 ohms
>to balanced 50 ohms, and transformers to convert from balanced
>50 ohms to balanced 450 ohms. The loss including the transformers
>is measured in tenths of a dB.
Another approach is to use a multi-wire open wire line, using 4 or more
conductors. I have heard of ones using as many as 16 wires configured in a
matrix with a variety of patterns in which sets of wires are parallelled
together at both ends. Such a configuration can drastically reduce the
surge impedance of the line, and slightly lower the loss at a given SWR. A
common arrangement in older broadcast installations was to use 5 wires to
form open wire "coax". The pattern is a square with a wire at each corner
and a 5th wire in the middle of the square. The wire acts as the centre
conductor, while the 4 outer wires forming the square are shorted together
at each end, to act as the "shield" of the coax.
Don k4KYV
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