rf properties of PVC

[sellington]

K1VR's use of PVC on his gamma rod is a good example of a situation in
which you CAN'T use PVC.  (No offence, Fred.)  There can be several
thousand volts at the end of the gamma rod, all of it across a few
mm of PVC.  Even if PVC were a good RF material, the voltage probably would
have been high enough to break it down.  (I destroyed a ceramic feed-through
insulator that way.)  On the other hand, if you use a horizontal piece of
PVC to hold the gamma rod away from the tower, that same voltage appears
across 1 foot or so of PVC, and there's no problem.  As a very rough 
rule, I'd recommend limiting the RF voltage across PVC to a couple volts
per mil (40-80 V/mm), below 30 MHz.

Scott   K9MA