VK2KC wrote:
Bob,
Have just wound a coil on 4" grey UPVC, but before I did I whacked it into
the microwave, and it certainly didn't show any signs of warming.
Maybe they have removed the carbon?



basically, RF loss is not a controlled parameter for manufacturing.
Sometimes it might be fine, other times not.

The Tesla Coil builders use lots of PVC pipe as coil forms (as well as
things like cardboard concrete forms: Sonotube(r)) and there is huge
variability in dielectric strength. I would imagine that RF loss also
varies substantially.

If you're really obsessing, the loss varies quite strongly with
humidity. PVC readily takes up and releases moisture from the atmosphere.