On Sun, 6 Oct 2013 00:32:22 -0700 (PDT), wrote:

I had always heard that if one were to use PVC, the gray type was
the best vs the white. I've used gray PVC for mobile whip loading
coils for years and never really noticed any real problems.
But, I do not run high power, and 100w is the max I run.
I've always had good results with the antennas, and noticed no
noticeable performance loss vs say an open type bug catcher coil.
There may be some, but it's small enough not to be a problem.

When I first started using the gray PVC, I stuck it in the
microwave with a glass of water, and it did not get warm at all.
I have heard the white PVC can be more of a problem.

http://lists.contesting.com/_towertalk/2006-12/msg00091.html

I ran tests at 2.4GHz about 15 years ago. The plan was to use PVC
pipe as a 2.4GHz antenna radome. While heating is obviously not an
issue at 1 watt, even small losses and detuning were deemed
intolerable. I couldn't measure any difference between grey or white
as long as the pipe was the same thickness. However, things went awry
when I tried to build prototypes out of a mix of different brands of
white PVC pipe. The dielectric constant was all over the map causing
the resonance point to move around. After determining that even a
single supplier can't keep their electrical characteristics
consistent, we switched to the more expensive fiberglass tubing and
lived happily thereafter.

Another potential problem with a base loaded vertical is not power,
but voltage. At 5 watts, there's not going to be much voltage across
the coil. At 150 watts, it might arc. No calcs today. Gotta run and
watch the solar satellite outage today.
http://en.wikipedia.org/wiki/Sun_outage

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558