I think the grey PVC electrical conduit is more sunlight resistant, but
I don't know about its insulation properties at UHF.
On 01/18/05 04:54 pm firstname.lastname@example.org tossed the following
ingredients into the ever-growing pot of cybersoup:
W7CJK here. I've used sked 40 and lighter for a number of experimental
antennas. Very convenient and cheap. It probably will be OK as to warp if
it does not cantilever (project from a support) more than three feet. I
built a double rhombic for 900 MHz with a twelve foot boom and used diagonal
wire struts back to the mast to support the ends which were six feet out. It
was up several years without incident before the experiment was terminated.
Don't remember now but it may have been 1" sked 40. Most of my experiments
used 3/4" stuff.
IMHO it's a good material for experimental use as most ham projects are. If
you plan a rather permanent installation, metal gives more reliability.
The directors and reflectors do not need to be insulated from the boom.
However, the exact length you need will vary depending on which way you go.
The center of the driven element may or may not need to be insulated,
depending on the type of feedpoint matching. I generally used gamma match
so the center of the driven element did not need to be insulated. On the
driven element, slight variations in design length can normally be corrected
in the matching process.
If you're fairly new to this stuff and following someone else's design, I
would follow the mechanical details as closely as possible. Minor changes
can alter the resonant frequency of the directors and reflectors enough to
seriously impair the directivity and gain.
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