300 ohm underground feedline
 

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?

Steve W9HJW

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

--
David Ryeburn

To send e-mail, use "ca" instead of "caz".

David Ryeburn wrote in message ...
In article ,
(Steve Beyers) wrote:

Centering the inner pipe inside
the outer pipe is important.
David, ex-w8EZE


How is the inner pipe held in the centered position?

Steve W9HJW

On 10 Aug 2004 19:22:28 -0700, (Steve Beyers)
wrote:

How is the inner pipe held in the centered position?

Steve W9HJW

Hi Steve,

Wrap a small tube around it loosely, like in a air core coax. -Hmm-
Have you thought of simply building a large scale coax?

73's
Richard Clark, KB7QHC

be careful about condensation - twin lead is pretty picky about its
surrounding

"Steve Beyers" wrote in message
om...
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?

Steve W9HJW


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I remember something about that - now that you mention it - but there was
some drawback other than price - I think it was lossy - but I may be in
error - going by memory
I once had a good memory - but forget where I left it.

"Tam/WB2TT" wrote in message
...

"Steve Beyers" wrote in message
om...
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?

Steve W9HJW

They used to make shielded 300 Ohm line. You could run that through
anything, so long as it is dry.

Tam/WB2TT




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