On Sat, 28 Aug 2010 13:44:24 -0300, Alejandro Lieber
wrote:

Somewhere I read not to use PVC for coil forms. Is it so ?

http://www.tangram.co.uk/TI-Polymer-PVC.html
Electrical properties
The insulation properties of rigid PVC are satisfactory and
those of plasticised PVC are poor. The values, which are
only mediocre in any case, are impaired still further by the
plasticisers. As a result of the high dissipation factor,
PVC is not suitable for high frequency applications.

PVC has a dissipation factor of about 0.0350 compared to about 0.00610
for Polycarbonate.
http://www.matweb.com

Black PVC is also loaded with a small amount of carbon pigment, which
likes to get warm/hot/melt when RF is applied.

PVC is also subject to dielectric absorption. Build a capacitor out
of two plates with some PVC in between. Apply some DC, remove the
power source, and short the plates for 2 seconds. Then measure the
residual voltage across the plates. PVC and vinyl are awful. Teflon,
polystyrene, and polypropylene don't have this problem.


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