On Thu,1/1/2015 4:41 AM, Rick - DJ0IP / NJ0IP wrote:
Keeping in mind that height is might, it is a lot easier for one OM alone to
erect an antenna high in the air when using lightweight components (e.g.
fiberglass telescoping pole, non-porcelain insulators, thinner Copperweld
wire, and thinner Kevlar or Dyneema rope), than with traditional heavy metal
poles and heavy wire and insulators.
Danger, Will Robinson! High antennas will end up on the ground if one
of their components is not mechanically robust. UV can quickly degrade
some of those lightweight components, like the bungees mentioned.
Several years ago, my good neighbor, an aero/mechanical engineer working
in the space program, advised me that rope made from Vectran, a new
space age material, was the ideal support rope for antennas. We bought a
500 ft spool. it was expensive, $300. I used a length of it to support
one end of my 160M Tee vertical. That was in early 2012. Last week, I
was re-rigging that antenna because the big Madrone that held up one end
had died, and had to be cut down. I had intended to reuse the Vectran,
but the tree guys used new rope instead. That turned out to be a good
thing -- upon inspection, the Vectran was badly degraded by UV, the
antenna would likely have been on the ground in another year, and I
would have been paying a climber to put new rope through that pulley.
High wire antennas are heavy, mostly because of the long attached
feedline. Lightweight components ARE a good thing when they reduce
antenna weight. i like the new lightweight egg insulators, for example
-- even if they do degrade with UV, the antenna is not going to end up
on the ground. Some hams use small coax on high dipoles to reduce
weight, but that small coax adds a lot of loss, so I use RG8 or RG11.
If you don't want a lot of sag (and we don't, because the loss of height
subtracts dBs from our signal), you need a lot of tension. Again, more
stress on components, like the center insulator.
"Thin copperweld?" AARGH -- I HATE copperweld. It's nasty to work with,
and its brittle. I've never used it. That same neighbor built an 80M
dipole with copperweld and hung it between two trees at about 90 ft. Two
days later it was on the ground -- the copperweld broke. He and I have
since standardized on hard drawn copper, which we buy as a 500 ft spool
of #8 bare copper from the big box store and stretch to make it hard
drawn. The process is pretty basic -- we cut it into suitable lengths,
tie one end to a fixed support (like a telephone pole or big tree), the
other end to the trailer hitch of his pickup, and pull very slowly until
it breaks. I first did this about ten years ago, and we've done this
several times since. We typically get about 20-25% stretch, so that 500
ft becomes more like 600 ft of #9 copper.
If you don't want to go to that trouble, #12 or #10 THHN (insulated
house wire) from the local big box store works very well. Yes, copper
stretches under tension, and I've had to lower and circumcise my high
dipoles every few years to keep them resonant where I want them. That's
a major reason I've gone to hard drawn copper.
I like copper split bolt connectors to secure mechanical and electrical
connections. Solder tends to make a joint brittle, and more likely to
fail mechanically if subject to movement, and high dipoles DO move. :)
To me, the place for those lightweight components is portable operation,
like Field Day.
73, Jim K9YC
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