[TowerTalk] 80 M 4 SQUARE MODELING
jimlux at earthlink.net
Sat Jul 22 09:27:54 EDT 2017
On 7/22/17 6:10 AM, Rudy Bakalov via TowerTalk wrote:
> I am in the exact same situation- 95' tower that I plan on using to suspend wire elements from the top of the tower.
> I assume THERE WILL BE interaction between the 4SQ and the tower. What I have been wondering is how mechanically reliable this setup is compared to elements made of aluminum tubing. Any thoughts on this?
> In addition, I have been wondering if the wire will stretch over time thereby changing the resonant frequency of the elements. Perhaps CAT5 might be a better option for the elements as it is less likely to stretch?
How much will it stretch (Or really, you're talking about creep over
time, stretch would be when you first hang it).
You could always use copper clad steel (CopperWeld) which has negligible
stretch or creep. Even hard drawn copper doesn't creep much.
Magnet wire or AWG12 house wire, maybe you'll have a problem? Design
your antenna so you're well below the yield strength of copper and it
won't permanently stretch.
Do a test - get a length of your wire, hang it up next to the tower with
a weight, and watch it for a month.
You could use a kevlar or spectran core with the copper twisted around it.
You could use Cable TV drop coax (which has a steel strength member) -
and use the aluminum shield as the radiating element.
You could rig your antenna so that the wire (attached at the ground at
one end) goes up to a pulley on the suspension cable, and then down a
few feet to a weight that is around the wire going up. That way it will
self adjust as the wire changes length.
you might be over-thinking this - how much change is too much? 1%? 5%?
You'll get about 0.1% change in length just from temperature swings.
That's where the model is nice - will a 1% change make any difference?
The model will tell you.
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