Somewhere, I read that the black plastic and grey conduit types were
unsuitable for antenna construction.
And, if I remember correctly, it was (claimed) due to carbon in the black
and metal oxide coloring in the grey...

Was this an old wives-tale?

Regards,
John

John Smith wrote:
Somewhere, I read that the black plastic and grey conduit types were
unsuitable for antenna construction.
And, if I remember correctly, it was (claimed) due to carbon in the black
and metal oxide coloring in the grey...

Was this an old wives-tale?

The thin plastic irrigation tubing has close to infinite
resistance and stays cool in the microwave. It is used
as spacers in presently available open-wire transmission
line.
--
73, Cecil http://www.qsl.net/w5dxp

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Cecil Moore wrote:
John Smith wrote:
Somewhere, I read that the black plastic and grey conduit types
were
unsuitable for antenna construction.
And, if I remember correctly, it was (claimed) due to carbon in the
black
and metal oxide coloring in the grey...

Was this an old wives-tale?

The thin plastic irrigation tubing has close to infinite
resistance and stays cool in the microwave. It is used
as spacers in presently available open-wire transmission
line.

Cecil, who sells that line??

--
73, Cecil http://www.qsl.net/w5dxp

w3rv


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Brian Kelly wrote:
Cecil, who sells that line??

http://www.w7fg.com
--
73, Cecil http://www.qsl.net/w5dxp


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Cecil Moore wrote:
Brian Kelly wrote:
Cecil, who sells that line??

http://www.w7fg.com

I've wondered what he's using. Tnx Cecil.

73, Cecil http://www.qsl.net/w5dxp

w3rv


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On 28 Apr 2005 10:23:55 -0700, "Brian Kelly" wrote:


Cecil Moore wrote:
Brian Kelly wrote:
Cecil, who sells that line??

http://www.w7fg.com

I've wondered what he's using.

It's 1/2" pipe, rated for 100 PSI in its original use; looks sturdy...

bob
k5qwg

Tnx Cecil.

73, Cecil http://www.qsl.net/w5dxp

w3rv


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Thanks Cecil/Atec... I have expanded my list of antenna materials! And, the
microwave will be my authority...

Warmest regards,
John

John Smith wrote:
Thanks Cecil/Atec... I have expanded my list of antenna materials!
And, the
microwave will be my authority...

You might wind up throwing the baby out with the washwater. Somebody
somewhere once pointed out to me that many materials have different
resistivities at different frequencies, the higher the frequency the
lower the bulk resistance. One implication being that a candidate
spreader material which gets hot in a 2 Ghz microwave oven does not
necessarily mean it will be at all lossy at 7 Mhz. The FCC human RF
exposure limits rules are based in this principle. Being a few feet
away from an antenna radiating 100W of 40M RF is not a problem, 100W
of 2 Ghz RF into the same antenna is deadly or close to it, etc.

About a year ago I picked up some 2"-3" scrap lengths of carbon fiber
composite hunting arrow shafts from a local sporting goods store and
put them to the microwave test. This material has an extremely high
strength/weight ratio which makes it attractive for use as spreaders.

They got pretty warm after nuking them for five or so minutes. Then I
checked several of them with my DMM set to it's 200 megohm range. In
all cases the DMM indicated completely open circuits. From this
experiment I've concluded that this material is plenty "good enough" to
use for HF feedline spreaders. Unfortunately it's a bit difficult to
drill & cut.


Warmest regards,
John

w3rv

On Wed, 27 Apr 2005 18:01:30 -0500, Cecil Moore
wrote:

John Smith wrote:
Somewhere, I read that the black plastic and grey conduit types were
unsuitable for antenna construction.
And, if I remember correctly, it was (claimed) due to carbon in the black
and metal oxide coloring in the grey...

Was this an old wives-tale?

The thin plastic irrigation tubing has close to infinite
resistance and stays cool in the microwave. It is used
as spacers in presently available open-wire transmission
line.

At work we had an issue with the use of nylong tie-straps on our test
fixtures that were used during RF testing (moderate power, Ka band).
Well, I'm in the mechanical side of the house but suggested the
microwave test & pretty soon I was surrounded by RF guys who heard
about my answer and were interested in why I thought that would work -
when I explained it they were not only satisfied it would answer their
concern but were rather impressed that a guy who does mechanical
ground support equipment came up with it. None of them were Hams. I
think it's great that our hobby can help us out in other ways.

Howard

John Smith wrote:
Somewhere, I read that the black plastic and grey conduit types were
unsuitable for antenna construction.
And, if I remember correctly, it was (claimed) due to carbon in the black
and metal oxide coloring in the grey...

Was this an old wives-tale?

Regards,
John


It is correct , normally testing the conduit in a microwave for 30
seconds works , if its not hot then its reasonably rf resistant .