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.
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|