The NEC requirement is based on the need for physical strength, the
concern being that it does not break and land on power conductors. Which
seems silly -- you gotta be crazy to run an antenna above power conductors!
ALL copper stretches, stranded or solid. I have an 80M dipole at 120 ft
between trees fed with RG11, and it has about 100# on one end. It's #10
stranded THHN. Every few years I have to lower it and circumcise it to
correct for the stretch (1-2 ft on each end). For years, I've bought #8
bare copper from the big box store and stretched it to make it hard
drawn. We tie one end to a tree or telephone pole, the other to a
trailer hitch, and stretch it until it breaks. This wire, roughly 20-25%
longer, doesn't stretch much more once it's in the air. One of these
days I'll rebuild that dipole with it.
I don't know of any science that says solid is more robust than stranded
when subjected to repeated flexing or other stress. There IS a
reasonable concern that BARE stranded is more subject to corrosion, but
THHN insulation provides very good protection against that.
73, Jim K9YC
On 12/5/2017 8:36 AM, Alan NV8A wrote:
I was quoting from a description of the NEC requirements rather than
from the NEC itself, and you are correct: that description does not
cover the situation where the antenna is exactly 150ft. long. Without
checking, my guess is that the NEC in fact says "150ft. or longer."
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