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Author Topic: Droopy Dipole Legs  (Read 1747 times)
KL3HY
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Posts: 117




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« on: October 19, 2011, 03:08:13 PM »

How important is it to stretch the legs of a wire dipole so that they don't droop?

I have a 135' off-center fed dipole and the short leg droops a little.  I'm limited in my ability to move the leg support mast further out because it would mean moving onto my neighbor's fence.  I'm going to approach him about doing just that, but in the event he says no I was curious about the droop factor.

I can also tighten it up by lowering the mast for that short leg, but I would think higher is better even if it means a little droop in the wire, but I could be way off there.

Any advice is greatly appreciated!
Mike
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N3JBH
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Posts: 2358




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« Reply #1 on: October 19, 2011, 03:34:02 PM »

some droopage is ok. Heck my wife has droopage  Grin    But really it wont hurt as temps change you have some to begin with. At least here in Pa. Summer comes antenna's sag winter comes there pretty darn tight.
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WB6BYU
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« Reply #2 on: October 19, 2011, 04:03:59 PM »

Having some sag is normal - you can never pull up enough tension to avoid it without
breaking the wire.

Generally I tie off the end of a wire antenna with a length of rope that goes through a pulley
(or a screw eye) at the top of the mast and down to ground level where I can tie the rope
off to something convenient.  Sometimes I hang a counterweight on the end to set the
tension on the wire - this is a particularly good idea if one end is a tree that blows in the
wind.  If you don't have room to pull your wire snug enough, lower the end down (that's
why the rope goes through the pulley) and move the insulator a few feet up the wire
close to the feedpoint, letting the end of the wire hang down.  Then pull it back up and
tie it off.  The ends have minimum radiation, so letting them hang down rather than running
straight doesn't hurt anything, and it allows you to make the rest of the antenna a bit
more straight.
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VE3FMC
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Posts: 983


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« Reply #3 on: October 20, 2011, 03:44:01 AM »

some droopage is ok. Heck my wife has droopage  Grin    But really it wont hurt as temps change you have some to begin with. At least here in Pa. Summer comes antenna's sag winter comes there pretty darn tight.


If your wife reads your comments you might be hurting  Grin
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W4VR
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« Reply #4 on: October 20, 2011, 12:06:20 PM »

I don't think it would hurt a thing.  Most of my HF antennas are center supported but horizontal.  I always leave droop in the wires so the tree sway won't cause the ropes to wear out.  If you have a 40 meter dipole, let's say, and you support it only on the ends at the 40 foot level I don't think the antenna would suffer if you have a 5-foot droop in the center.
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AK7V
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Posts: 247




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« Reply #5 on: October 20, 2011, 02:06:46 PM »

I use an 80 meter doublet supported only at the ends.  There's at least 6 feet or so of "droop" but the antenna works fine.  Fortunately (?) there's also corresponding "droop" on the ground because the antenna spans a dry creek bed that's about 10-15 feet deep. Smiley
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W3PO
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Posts: 38




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« Reply #6 on: October 21, 2011, 01:50:36 AM »

Mike,
I also added in between the end of the supporting line and the pulley one of those garage door spring which will take the tension of a tree swaying.
My old sloping Vee beam had plenty of droopage and did all-right.
Unless you have excellent rapport with your neighbour I would keep it all on my lot.
I even go as far as when asked I tell them it is a shortwave listening antenna, as in the past as soon as they know I was transmitting a signal, TV, stereo and other problems suddenly became my fault.
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73 de Pat W3PO
NA0AA
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Posts: 1043




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« Reply #7 on: October 21, 2011, 09:04:40 AM »

I think you mean the supports are not quite far enough apart.  No huhu, my 80 m dipole has about 5' on each end that hangs down from the support.  It works fine.
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KL3HY
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Posts: 117




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« Reply #8 on: October 21, 2011, 03:14:02 PM »

Thanks guys, this kind of confirms what I was thinking.  I'm probably going to leave it as-is over the winter.  It works well enough that I can clearly pick up HFGCS stuff on 11175 and 8992 kHz very clearly, and I've been able to check into a couple local HF nets on 75m and 40m.

Next spring I already plan on raising the center mast at least another 4' to get the balun higher, and I'll raise the end of the short leg appropriately.

Thanks again!
Mike
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