The question of the suitability of PVC for antenna work comes up often on the net. I have answered that question often. The short answer is that it is OK to use PVC in most amateur applications. A more detailed answer is given below. On the towertalk reflector, Sig, R. Sigismonti, n3rs, asked: "Wonder if anyone could comment on the use of 4" OD PVC Tubing as a form for a loading coil that will be used in an above ground shortened radial system on each element of a 4-SQUARE? Should I hunt around for Polyethylene or is the PVC OK for this type application." The PVC should be OK, particularly in the fairly large diameter you propose using. The losses at HF for PVC are not all that much worse than other dielectrics often reccomended for RF use. However PVC does have a lower softening point than most other plastics, which can lead to problems if losses are excessive. PVC got its bad rap from a picture in QST 20 or more years ago. It showed a PVC former that had been used for a loading coil on a 160 M antenna that had softened and split open due to excessive losses. This is a pathoglogical case though. The coil shown in QST was long and thin, had a low Q and high losses. It was also wound with small diameter wire which further compounds losses. In one of the recent Antenna Compendiums there was an article on mobile antennas . The author compared two inductors; one wound on a PVC former and one air wound. The PVC former was only slightly lower and the author concluded that it was acceptable for use as loading coils. I don't know how many radials you are going to load, but the total power dissipated gets divided by the number of radials which further reduces the losses in any indiviual coil. The best way to evaluate the PVC former in this use is to use it in the application and see if it gets hot. Build a few radials, run them with the power you are going to run for a while and see if the PVC Coil gets hot. Don't touch it with power applied. :^). If the PVC doesn't get too hot you should be ok. Some recommend using a microwave oven to determine losses in materials. However the losses at microwave frequencies can be much different than those at HF, so you may as well do the tests at HF anyway. Besides there are better experiments to do in the microwave! I hope that this helps. - Dr. Megacycle KK6MC/5