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Author Topic: Amount of sag in a dipole type of antenna  (Read 1784 times)
K2OWK
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Posts: 1036




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« on: March 16, 2012, 08:47:42 PM »

Hello experts,

    I have a question. I was wondering what effect sagging antenna lines (driven) have on performance? I have three inverted "V" antennas. One on 40 meters one on 10 meters and one on 6 meters. The 40 meter antenna has developed quite a bit of sag on both wires. When I put it up it had very little. The antenna has a good VSWR 1.3 to 1 on most of the band and still appears to work the same as it did when the wires were tight. The other two the wires are tight and they also work well.
I do not want to stress the wires on these antennas especially the 40 meter, as I am worried they may break, the 40 meter has been up about three years. The antennas use #14 stranded insulated wire. Again any problems with having sagging antenna wires?

Thanks and 73s

K2OWK
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N4JTE
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« Reply #1 on: March 16, 2012, 09:59:40 PM »

Are they all on same support? If so something needs to be tightened to avoid screwing up the the other bands, need more info to help.
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WB6BYU
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Posts: 13015




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« Reply #2 on: March 16, 2012, 10:17:02 PM »

Generally sag isn't a problem.  But if the wires on an inverted vee sag too much
the angle gets too narrow at the feedpoint and the efficiency (and radiation
resistance) drop a bit.
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KI4SDY
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Posts: 1452




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« Reply #3 on: March 17, 2012, 01:04:27 AM »

If you had installed pulleys and weights (I use nylon pulleys from Lowes and red bricks with holes in them for weights) on one end or both (the KI4SDY storm resistant method with the center supported by a nylon cord with pulleys and weights on both ends, even on flat dipoles) they would not sag and you could instantly convert your flat dipoles to inverted V by pulling up the center conductor. Any 14 AWG stranded wire in good shape will not break by being weighted at one or both ends with a brick and they are more likely to survive a bad storm.  Wink
« Last Edit: March 17, 2012, 01:11:34 AM by KI4SDY » Logged
W4VR
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« Reply #4 on: March 17, 2012, 08:47:55 AM »

Sounds like the wire has stretched.  14 gauge is a little small.  I use stranded 10 gauge with the insulation on and never had a problem with stretching.  My antennas are horizontal, but the longer ones such as the 75 and 40 meter dipoles have center supports to minimize sagging due to coax weight (RG213).
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K7KBN
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Posts: 2758




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« Reply #5 on: March 17, 2012, 10:42:32 AM »

A bit of sag is unavoidable with most wire antennas on HF.  To minimize the wire stretching, you can use Copperweld, or hard-drawn copper (both dreadful to work with).
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73
Pat K7KBN
CWO4 USNR Ret.
N8CBX
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Posts: 130




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« Reply #6 on: March 17, 2012, 01:34:02 PM »

When I recently made my trapped 160/80/40 dipole, I noticed a bit of stretching and would throw the 160 & 80 out of tune (this is right after I mounted close to the ground for its first swr test). I took it back down and pull tested it to about 30-40 lbs, and it was stable after that.
Jan N8CBX
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Dayton Ohio - The Birthplace of Aviation
K0IZ
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« Reply #7 on: March 17, 2012, 04:49:54 PM »

Most of us get some sag as the years go by.  But SWR still good....
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K2OWK
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« Reply #8 on: March 17, 2012, 05:29:42 PM »

N4JTE, To answer your question each antenna is completely separate (different locations on the same property). The 40 meter antenna is tied between two trees who's branches are sagging. The ends are to far up for me to reach easily at this time (I am in my 70s). I am getting the information from this post, that it should not matter to much if it is sagging as long as the VSWR is still good. Thanks for the information.

73s

K2OWK
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WB6BYU
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« Reply #9 on: March 17, 2012, 06:02:26 PM »

That's why I always tie my antennas off at ground level, or at least within easy reach.
That also allows you to put a counterweight on the end to maintain constant tension
even when the trees blow in the wind.
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