[TowerTalk] Delrin End Insulators

[Tom Rauch]

I never knew about the water absorption. Never caused a
problem here.

> If we assume about 5pF of stray C from the center
insulator,
> a 70 ohm feedpoint impedance, and 1.5 KW at 4 MHz, a DF
> of .027 would correspond to about 350 milliwatts of
dissipation
> in the center insulator. Not enough to even cause a
noticeable
> rise in temperature. Perhaps water absorption might make
> this worse, but I don't know if that will have much effect
at 4MHz.

I ran the same exercise with tank circuits. Delrin makes no
difference there in place of ceramic, nor does it make a big
difference in a roller inductor.

> I am a little worried about the end insulators, however,
as its
> not clear to me how one goes about predicting the
capacitance
> and voltage at the ends of a dipole (e.g. what is the
reactive
> power flowing in the end insulator).

I've never had a problem at all and I've used it in HV
applications outdoors for years in some antennas with pretty
high voltages....like across the feedpoint of two half-waves
in phase.

I can't imagine it being a problem when you have a rope past
it on an open antenna end!!

73 Tom