On 12/28/16 11:09 AM, Jim Brown wrote:
There's another very practical issue with the use of ordinary copper
wire for antennas hung between supports -- copper stretches! I found
that my high dipoles strung between trees at 130 ft with the tension
needed to keep then sort of horizontal with 160 ft or so of RG11 trying
to drag them to the ground stretched enough that I must lower them and
circumcise them every few years.
This is why the NEC Article 800 (which, as far as radio antennas go, I'm
convinced was written back in the days of king spark) requires
hard-drawn copper or copperclad steel of no less than 14 AWG. My
contention is that all those AWG 20 antennas we put up are "temporary"
and hence not covered by the NEC.
Skin depth in copper at 2 MHz is 1.8 mil. A good rule of thumb says
that if the cladding is >5 skindepths, then the properties of the core
make no difference (even if it's steel)
21% copperweld AWG 14 has a cladding that is 1.9 mil - the steel is
going to make a difference on top band..and even on 20m (skin depth 0.7mil)
40% IACS has 6.4 mil cladding.. that's about 3 skin depths.. probably ok
on TopBand, definitely not a problem on 20m (9 skin depths)
Of course, then you have to deal with the nightmare that is handling
CopperWeld in all of its evil want to coil on itself badness.
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