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