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300 ohm underground feedline

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August 10th 04, 10:54 PM

David Ryeburn

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In article ,
(Steve Beyers) wrote:

In the past, I've seen several references here to feedlines consisting
of 300-ohm transmitting-type twin lead buried in PVC pipe. Does
anyone have any suggestions on what size pipe to use, and how to keep
the line centered in the pipe?

Use two concentric PVC pipes, the diameter of the smaller one large
enough to admit the twin lead and the diameter of the larger one large
enough to keep the surrounding ground far enough away. I should think
that 10 times the twin lead wire spacing ought to be far enough.

Centering the twin lead inside the inner PVC pipe is unimportant,
assuming that the PVC is low-loss stuff. Centering the inner pipe inside
the outer pipe is important. Keeping water, ground, and other things out
of the space between the pipes is important.

Make sure you don't have common mode current on the twin lead; it won't
radiate very far if you do, but you may overheat some earthworms.

Or you could just use coax and avoid the problem ;-)

David, ex-w8EZE

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David Ryeburn

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