On 11/1/18 10:12 PM, Jim Brown wrote:
On 11/1/2018 8:58 PM, Tom Osborne wrote:
Did you look at the Flex Weave wire. It is pretty strong and
lightweight.
I did NOT find it strong -- I bought and used #12 and #14 bare and
insulated to try. Every antenna I built with it was on the ground within
a year.
For lightweight, backpacking antennas, I like insulated #18 or even #22.
They're not strong either, but I'm talking backpacking, hiking, etc.
You can get some "highly flexible" multistrand PTFE insulated wire
that's quite small and "limp" in fairly small gauges (#24 or smaller)
The key is the high strand count,rather than the usual 7x32, it's 19x36
strands.
#24 has an od of 0.036". #22 is 0.042"
I've not looked at the tensile strength.
What about something other than copper? Stainless steel unfortunately
has a high resistivity (69 vs 1.68 microohm-cm for copper)
Hmm, tungsten is really, really strong and it's only 5.6 microohm-cm -
We used to use it to "invisibly" hang things in the special effects
business.
Iron (not steel) is 10 microohm-cm but because it's magnetic, the skin
depth will be really thin.
AWG 20 is 32 mils in diameter
Skin depth at 10MHz for copper is 0.8 mils, so you're really only using
the outer 10% of an AWG 20.
If you use tungsten (for example) the resistivity is about 3 times
higher, but the skin depth is 1.5 mils, so overall, the AC resistance is
going to be 1.5 worse than copper.
And, just how much loss is there from using a more resistive wire?
What's the "copper loss" in a half wave dipole for 40 meters made of AWG
20 instead of AWG 14?
A 20 m length of AWG 14 has a ac resistance of about 1 ohm at 10MHz, and
AWG 24 has about 3.5 ohms.
Against your nominal 72 ohm antenna Z, that's not a huge loss, 5%
Enameled copper is great for antennas that need to be hard to see.
But it kinks easily, and get stuck in trees.
73, Jim K9YC
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