Thanks for all your comments, Jim. I think I've seen different dissipation factor values for PVC depending on filler amount. I believe I used values for pure PVC, but I can't remember. In any event, with other dielectrics so readily available, I think PVC pipe should be avoided. By the way, cardboard is the lossiest dielectric my program lists. I included it for the oatmeal boxes builders traditionally used for crystal sets.
Some dielectrics like PVC are lossier at HF than UHF and some show the opposite behavior. That's why I think the microwave oven test can be very misleading.
Brian
