[TowerTalk] A couple of 18HT questions

[Jim Lux]

On 12/16/14, 3:51 PM, Allen Brier N5XZ wrote:

>
> 3.       I have been told that the PVC insulators which are at the top of
> the top tower section should be replaced with Teflon due to high voltage at
> that point while using the antenna on 160 meters with the base loading coil.
> (Note I plan to use a larger physical coil than Hy-Gain recommends). Any
> truth to that?
>

PVC is slightly more hygroscopic than PTFE (Teflon) and a heck of a lot 
cheaper.  The high voltage breakdown strength of either is probably more 
than you need.

PVC burns at a lower temperature, so if you intend to light your antenna 
on fire, this might be an issue. It also softens at a lower temperature.

If you want a replacement for PVC, I'd suggest High Density PolyEthylene 
(HDPE) which is readily available as those white cutting boards.  HDPE 
saws and drills nicely (with sharp teeth/edges), is extremely 
inexpensive (18x24" cutting boards are <$10).  It also welds well.

HDPE has basically the same dielectric breakdown properties as PTFE, at 
least in forms you're likely to use as a structural component.

The big problem with HDPE (and PTFE) is that they're exceedingly hard to 
glue to anything.  PVC, ABS, etc. all have glues available.

If you want something else insulating, then there's a variety of 
glass/epoxy composites.  Garolite is one name, FR-4, G-10, etc. They are 
low loss at HF, cheap, and quite a bit stronger than any of the regular 
plastics.

Extren structural members are basically the same strength as aluminum, 
but more flexible.