>From what I understand, the RF properties of PVC pipe are quite
variable depending on the additives included.
I've used it for all sorts of antenna applications and not had a
problem, but I've never stressed it more than using it for end
insulators on a dipole while running 100W. I wouldn't use it as a
substrate for microwave circuitry, but plenty of hams use it for HF
all the time, even radomes for homebrew VHF antennas.
On the other hand, few amateurs actually measure the gain of the PVC
encased antenna vs. the bare antenna, so maybe it's not so great after
all. If you're losing 1.6dB from your PVC encased 146MHz collinear
over the bare antenna case, you're not going to notice unless you can
make a very good measurement.
I expect the loss at HF to be low enough, though, that the benefit of
keeping birds off (if it works) would outweigh the likely slight loss
in the PVC.
Dan
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