On 7/4/23 11:16 AM, WB2UAQ wrote:
Mike and Alan,
I measured the loss factor for PVC and it was about 0.005 or so at 1 kHz. I did more measurements at RF but will have to go back to old note books. I made a simple fixture to test a number of plastics. I rebuilt a coil that plugs into a BC-610 transmitter and from that sprung all kinds of questions about dielectrics. Many local guys are using 3D printers and using PLA, I think it is called. They printed out a plate of it for me to test. I would not say that all of this material is made equally and permitivity and loss factor are probably not well controlled. Won't be able to get back to this for awhile as it is Independence Day and a lot going on to take care of this week. Can only say right now that none of this plastic seemed to jump out as being a terrible dielectric. I also tested plate glass because back in the early days of radio capacitors for spark transmitters used what I think was regular glass available at that time.
PVC pipe has two potential problems as a coil form (based on experience of folks building tesla coils, so 100-500 kHz):
1) it's hygroscopic so the dielectric loss varies with the water content - nylon has the same problem, BTW.
2) most pipe is made from recycled material, and it can have metal fragments and other debris in it. The specs for pipe are about holding pressure and being "safe for drinking water", not dielectric properties.
Tesla coil folks solve #1 by drying it and then coating with something like lacquer, glyptal, or urethane
#2 is a bit trickier - it's not like you can take a 4 foot long piece of 6" pipe and throw it in the microwave and see if it arcs or has hot spots.
