On 3/18/21 3:51 AM, john@kk9a.com wrote:
My 40m OptiBeams use black clamps, I am not sure of the manufacture
but they look like Stauff clamps. I wonder who is saying that the
black clamps have a carbon issue? Can you buy one and test it?
John KK9A
There are so many black colored plastics of so many different bulk
resistivities and/or RF properties, you'd have to measure one to find out.
It is true that some black plastic uses carbon black as a filler to
improve UV resistance. But hey, they also use Titanium dioxide (which is
white) as a UV resistance improver. And there's other ways to get UV
resistance (as by using a different kind of plastic).
There are plastics deliberately designed to be conductive or dissipative
(for ESD protection purposes, usually). But whether they are DC
resistive doesn't tell you a lot about the RF properties.
The other thing is that, like plastic pipe, the composition of the
plastic in components is not the same from unit to unit. If it's a
clamp, they're concerned about things like mechanical properties, maybe
CTE or thermal properties. The mix of plastic going into the molding or
machining process could vary substantially - depend on what was in the
bins of recycled plastic, etc. When I used to build HV equipment, we
used a lot of pvc pipe (normally a good insulator), but we always had to
test it first, particularly if it was a leakage sensitive application.
For most plastic, there's a sort of gross conductivity check - people
expect plastic to be an insulator - but that's about it.
Byron W5FH wrote:
Hello- I am a little confused about the UV and electrical
properties of the polyamide insulator clamps (hydraulic and tubing
line support clamps) used on the VHF LFA yagis. I have viewed
commercially produced VHF LFA yagis that utilized green colored ones
to support 13mm tubing elements. I have read the black ones are better
in regards to UV resistance. However, some antenna manufacturers state
the black colored clamps have additional carbon in them and the
antenna element lengths will need adjusting. My head is nearly
spinning after trying to research this. I have tried to look through
the thousands of polyamide clamps in the Stauff catalog. Can anyone
shed any light on whether the green colored polyamide clamps, such as
used on an E-Antenna 6 meter 7 element LFA yagi, are inferior in
regards to UV resistance? I see where a competitor (making mostly HF
yagis) states the black clamp assemblies they use are better in
regards to UV resistance of the green ones that E-Antenna uses, but I
wonder if the black clamps have identical electrical properties or
would corrections need to be made to elements? I see where G0KSC, an
authority on the LFA and their construction, offers the green colored
clamps. Thanks, Byron W5FH
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