John Smith wrote:
Thanks Cecil/Atec... I have expanded my list of antenna materials!
And, the
microwave will be my authority...

You might wind up throwing the baby out with the washwater. Somebody
somewhere once pointed out to me that many materials have different
resistivities at different frequencies, the higher the frequency the
lower the bulk resistance. One implication being that a candidate
spreader material which gets hot in a 2 Ghz microwave oven does not
necessarily mean it will be at all lossy at 7 Mhz. The FCC human RF
exposure limits rules are based in this principle. Being a few feet
away from an antenna radiating 100W of 40M RF is not a problem, 100W
of 2 Ghz RF into the same antenna is deadly or close to it, etc.

About a year ago I picked up some 2"-3" scrap lengths of carbon fiber
composite hunting arrow shafts from a local sporting goods store and
put them to the microwave test. This material has an extremely high
strength/weight ratio which makes it attractive for use as spreaders.

They got pretty warm after nuking them for five or so minutes. Then I
checked several of them with my DMM set to it's 200 megohm range. In
all cases the DMM indicated completely open circuits. From this
experiment I've concluded that this material is plenty "good enough" to
use for HF feedline spreaders. Unfortunately it's a bit difficult to
drill & cut.


Warmest regards,
John

w3rv