The problem with all of this discussion is the casual use of the term 'RF
fields". In fact, the electric field inside of a solenoidal inductor (a/k/a
choke) is quite small, almost negligible. The large RF solenoidal field is
predominantly magnetic. The dissipation factor of plastics relates to their
absorption of the electric field (E) and is not relevant here, and there are no
materials present which present losses to magnetic field (H). The latter, of
course, is exactly the problem you run into when you try to use a ferrite core.
I have built all of my plate chokes out of PVC for the past 20 years, and PVC
is a fairly "lossy" dielectric. I like it because I live walking distance
from a good hardware store! But the heat generated by the chokes is always
dominated by the loss of the copper itself, not the plastic form.
In other components, there can develop large RF electric fields if the
plastic is used to any extent as an insulator between high-potential RF and
If the spacing decreases significantly below an inch, then the field
(gradient) grows and dielectric losses can and will occur. That is when teflon
becomes necessary. Nylon and all of its variations (including Delrin) are
These effects can all be readily calculated using simple capacitance
formulas. I have done it many times and never melted a piece of plastic or
my favorites for RF construction.
For those interested in the relative losses of different kinds of materials,
there is a good summary of the RF loss properties of the various common
plastics materials in an article I wrote several years ago that focused on the
construction of capacitors in gamma matches, where it is a highly significant
issue. Just send me a request for a copy of that article in MS Word format.
Eric von Valtier K8LV
Amps mailing list