We have a textbook that has a formula for insulation loss showing it is
directly proportional to frequency without any discussion of
exceptions. Of course, a resonant amount of material would behave
uniquely at its self resonant frequency. But, I won't belabor the
insulation test.
I think we all agree that PVC has higher capacitance loss factor than
other insulators such as poly plastics. They have not offered
polyethylene zip cord to my knowledge, but I sometimes look up the
product data sheet if there is one. The zip imports typically don't
have enough info to track their formulas.
We have had strong correlation at HF with small high intensity field
folded antennas being designed in the lab, with the microwave test of
modern plastics samples. When PVC frames were replaced with fiberglass
board supports for antenna elements, the antenna efficiency went up in
the Wheeler cap tests.
Sadly for RF use, in zip cord, PVC seems dominant in present, mostly
imported, cabling. PVC has also taken over the pipe market, but for
coil forms, you can find the effects of the PVC factors and compensate
coil designs that use this material.
L. B. Cebik's web site, <www.cebik.com> also covers avoiding some PVC
pipes that have additives in the plastic. In reference to PVC use in
atenna construction and element support.
As a first order screening test, a microwave sample tested for heating
is easy for any ham almost anywhere in the world.
Test and verify---
-Stuart
K5KVH
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