Thanks. I have a 70's vintage Standard Handbook for Electrical
Engineers somewhere. It may list the materials and dissipative
factors.

Ted KX4OM
On Tue, 29 Mar 2005 12:26:01 -0800, Roy Lewallen
wrote:

I should also mention that the requirements for an insulator depend
heavily on the application. An insulator which results in a lot of loss
when a large electric field is present might produce negligible loss
when the field is weak. For example, an insulator at the base of a very
short or half wavelength high vertical, or at the end of a dipole, has
to be pretty good in order to minimize loss, because the electric field
is high at those points. On the other hand, a poor quality insulator is
just fine at the base of a quarter wave high vertical or the center of a
half wave dipole, since the electric field is low at those points.

Roy Lewallen, W7EL