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Author Topic: how heavy is a wire antenna.  (Read 45796 times)
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WA1GFZ
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« on: November 26, 2005, 08:31:53 PM »

Today I built a new 160 meter antenna after a falling tree ripped my 1983 antenna apart. A 500 foot spool of #8 weighs 25 lbs so 250 feet is 12.5 LBS. the feed line is #10 with a johnson spreader every 30 inches the weight was about the same as the antenna for the 75 foot run to the shack. It is interesting that all that wire is actually
light. We all hope for good luck when th eice comes but my last antenna with Dual #10 twisted never had an ice failure. I've never had good luck with smaller wire for a 125 foot or longer span. #14 is ok for 65 feet but still a bit light.
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K1JJ
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« Reply #1 on: November 26, 2005, 11:08:59 PM »

I heard an old buzzard W1 on 75M years ago. Someone axed him why his dipoles never fall down.  He said the trick is to have the center supported. Once supported at the center, the legs can just float loose and are impervious to wind, ice and tree sway.

He was right.   Do you have YOUR center supported glasshoppa?... Grin  [or is your 60' tower too far from the center?]


T
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WA1GFZ
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« Reply #2 on: November 26, 2005, 11:53:37 PM »

Tom,
Center support is in the tree in the front yard and the antenna is a Vee facing west.
The back propperty line is 165 feet so a bit wider than 90 degrees. The tower is in the middle of the antenna. It would have been perfect 70 feet high now but the trees would have been too close. At least this will get me back on 160
The ends will be up in the tops of 2 oaks up 75 to 80 feet. a bit JSed for now but one more big elm needs to fall down before I can use the 100 foot tree in the neighbor's yard. Yup center support is a big deal.
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K1JJ
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« Reply #3 on: November 27, 2005, 01:42:55 AM »

With the center supported, I wouldn't worry about that antenna at all, OM..  esp with the big gauge wire.

I've had up #10 in full sized loops at 190' high for 6 years now. No problem with ice storms. You've seen the distance the rope holds up the legs.  Big span.  Resonant freq still the same.

T
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Jim, W5JO
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« Reply #4 on: November 27, 2005, 02:42:41 PM »

Supporting the center in a tree can cause problems in an ice storm only if a limb above the antenna breakes and falls across a leg of the antenna.  If you have that problem solved, and pulleys at each end with the end ropes weighted, you have it made.  The ends will then move through the pulleys as weight increases and decreases.
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W1IA
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« Reply #5 on: December 01, 2005, 10:28:41 AM »

Today I built a new 160 meter antenna after a falling tree ripped my 1983 antenna apart. A 500 foot spool of #8 weighs 25 lbs so 250 feet is 12.5 LBS. the feed line is #10 with a johnson spreader every 30 inches the weight was about the same as the antenna for the 75 foot run to the shack. It is interesting that all that wire is actually
light. We all hope for good luck when th eice comes but my last antenna with Dual #10 twisted never had an ice failure. I've never had good luck with smaller wire for a 125 foot or longer span. #14 is ok for 65 feet but still a bit light.
I got a 300 ft run of #10 copper weld for the double extended zepp...going to start assembly today....I could center support, but may cause an angle to the antenna....how much is too much angle? should I run without the center support and take my chances? It will have about 75 pounds of counter weight on one side.

Brent
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K1JJ
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« Reply #6 on: December 01, 2005, 11:16:00 AM »

I got a 300 ft run of #10 copper weld for the double extended zepp...going to start assembly today....I could center support, but may cause an angle to the antenna....how much is too much angle? should I run without the center support and take my chances? It will have about 75 pounds of counter weight on one side.

Brent

Brent,

Just like an inv vee in the vert plane, in the horiz plane, the leg cancellation [and lower input impedance] starts getting severe after you get lower than a ~90-120 degree angle between the legs.  [180 degrees being straight legs]  ie,  keep the legs in the horizontal plane  more than ~ 120 degrees apart and you're OK. 

I would imagine in your case, you're talking about something like 160 degrees or so, so it will not have any real whirl measureable effect in the pattern or input impedance, OM.

T
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WA1GFZ
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« Reply #7 on: December 01, 2005, 11:59:08 AM »

Brent,
75 pounds sounds quite heavy. That puts a lot of strain on the branch. I prefer less tension to use higher smaller branches.  I've had no failures since I let things hang a little looser. Supporting the feed line seems more of a strain than holding up the ends. My new antenna feed point is through the very top branches of a maple.
the whole feed point is supported by a 2 inch diameter branch. The open wire line
is fairly heavy #10 with 4 inch johnson spreaders. I started on a big branch at 35 feet then shot a line over the tree to get another 15 feet of hieght. The ends are at 65 and 75 feet. We had some pretty good wind the past few days with no problems.
I figure Ice may drop it down a bit but it will also pick up more branches to distribute the load. A 75 pound counter weight would have broken the branch by now. I figure there may be 25 or so pounds tension on the rope. I may add a support in the middle of the feed line to help hold it up. Maybe the 35 foot rope will be pressed into service. One end goes through the top of an oak and I bet there is only about 15 or 20 pounds tension. The wire doesn't droop enough to even consider pulling up tighter after gaining the extra height.  fc
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W1IA
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« Reply #8 on: December 01, 2005, 01:08:19 PM »

Brent,
75 pounds sounds quite heavy. That puts a lot of strain on the branch. I prefer less tension to use higher smaller branches.  I've had no failures since I let things hang a little looser. Supporting the feed line seems more of a strain than holding up the ends. My new antenna feed point is through the very top branches of a maple.
the whole feed point is supported by a 2 inch diameter branch. The open wire line
is fairly heavy #10 with 4 inch johnson spreaders. I started on a big branch at 35 feet then shot a line over the tree to get another 15 feet of hieght. The ends are at 65 and 75 feet. We had some pretty good wind the past few days with no problems.
I figure Ice may drop it down a bit but it will also pick up more branches to distribute the load. A 75 pound counter weight would have broken the branch by now. I figure there may be 25 or so pounds tension on the rope. I may add a support in the middle of the feed line to help hold it up. Maybe the 35 foot rope will be pressed into service. One end goes through the top of an oak and I bet there is only about 15 or 20 pounds tension. The wire doesn't droop enough to even consider pulling up tighter after gaining the extra height.  fc
Steel cable with pulley, so weight is not a factor....antenna assembled and now do or die.....I got to drag all this crap back in the property and lay it out......I could use some help, but I will do the Tom Vu approach.


Brent
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WA1GFZ
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« Reply #9 on: December 01, 2005, 02:37:43 PM »

That pulley will have to attached to something. The heavier the load the bigger the branch that needs to support it meaning you will have to use a lower branch.
The use of a lower branch forces the antenna to be tower no matter how hard you pull on the ends. In my case it was a good 15 feet. When the ant was raised to the top of the tree the resulating sag was still well above the previous position pulled up tight. my 160 ant was up 22 years before the falling tree ripped it down. It needed to be restrung anyway since the trees are a lot taller now. fc
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W1IA
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« Reply #10 on: December 01, 2005, 02:59:38 PM »

Brent,
75 pounds sounds quite heavy. That puts a lot of strain on the branch. I prefer less tension to use higher smaller branches.  I've had no failures since I let things hang a little looser. Supporting the feed line seems more of a strain than holding up the ends. My new antenna feed point is through the very top branches of a maple.
the whole feed point is supported by a 2 inch diameter branch. The open wire line
is fairly heavy #10 with 4 inch johnson spreaders. I started on a big branch at 35 feet then shot a line over the tree to get another 15 feet of hieght. The ends are at 65 and 75 feet. We had some pretty good wind the past few days with no problems.
I figure Ice may drop it down a bit but it will also pick up more branches to distribute the load. A 75 pound counter weight would have broken the branch by now. I figure there may be 25 or so pounds tension on the rope. I may add a support in the middle of the feed line to help hold it up. Maybe the 35 foot rope will be pressed into service. One end goes through the top of an oak and I bet there is only about 15 or 20 pounds tension. The wire doesn't droop enough to even consider pulling up tighter after gaining the extra height.  fc
Steel cable with pulley, so weight is not a factor....antenna assembled and now do or die.....I got to drag all this crap back in the property and lay it out......I could use some help, but I will do the Tom Vu approach.


Brent

Suks...I got to putting up ant only to find I am about 10-20 feet short in order to put up the 300 footer.
I guess I could droop the ends 10-20 feet per side?

Brent
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K1JJ
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« Reply #11 on: December 01, 2005, 03:42:32 PM »

Suks...I got to putting up ant only to find I am about 10-20 feet short in order to put up the 300 footer.
I guess I could droop the ends 10-20 feet per side?
Brent

Brent,

No problem, OM.  You're using open wire anyway.  Trim off the extra 10'-20'. The difference in pattern sharpness will be insignificant and within 0.1db.  It's better to have the dipole flat and straight at it's highest height than try for more gain via extra length with a sagging structure that will give it back via ground losses...

T
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« Reply #12 on: December 01, 2005, 03:46:53 PM »

Suks...I got to putting up ant only to find I am about 10-20 feet short in order to put up the 300 footer.
I guess I could droop the ends 10-20 feet per side?
Brent

Brent,

No problem, OM.  You're using open wire anyway.  Trim off the extra 10'-20'. The difference in pattern sharpness will be insignificant and within 0.1db.  It's better to have the dipole flat and straight at it's highest height than try for more gain via extra length with a sagging structure that will give it back via ground losses...

T


Isn't that how Mae West met her end?
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W1IA
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« Reply #13 on: December 01, 2005, 03:52:45 PM »

Suks...I got to putting up ant only to find I am about 10-20 feet short in order to put up the 300 footer.
I guess I could droop the ends 10-20 feet per side?
Brent

Brent,

No problem, OM.  You're using open wire anyway.  Trim off the extra 10'-20'. The difference in pattern sharpness will be insignificant and within 0.1db.  It's better to have the dipole flat and straight at it's highest height than try for more gain via extra length with a sagging structure that will give it back via ground losses...

T


I am bummed JJ, but thanks...I guess I will shorten it. It would be flat and high with the ends dropped down in the vertical plane.  Is it worth it? I hate to shorten it.

B
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K1JJ
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« Reply #14 on: December 01, 2005, 04:02:42 PM »

I am bummed JJ, but thanks...I guess I will shorten it. It would be flat and high with the ends dropped down in the vertical plane.  Is it worth it? I hate to shorten it.
B

Naw, shorten it.  The pattern is way to narrow anyway as a double extended zepp. I modeled W2ZM's and he was yellowfied when he found how narrow his was. Gotta be rotary to be useful at that beamwidth on 75M.  You will gain a few tenths, but give up 10db more quickly when off center.

If ya really wanna get some gain, shorten it to 285' and put a set of side by side refelectors behind it. Now youse got f-b and 4-5db more gain. If you're gonna play the game, go for the height and f-b.  Forget the drooping legs cuz you already have enuff room to put up a good gain ant. No need to stretch it out the extra 20' vertically, OM.  Guys do that to get the input impedance and efficency up on a shortened dipole, but not in your case.



T
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There's nothing like an old dog.
W1IA
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« Reply #15 on: December 01, 2005, 05:38:50 PM »

I am bummed JJ, but thanks...I guess I will shorten it. It would be flat and high with the ends dropped down in the vertical plane.  Is it worth it? I hate to shorten it.
B

Naw, shorten it.  The pattern is way to narrow anyway as a double extended zepp. I modeled W2ZM's and he was yellowfied when he found how narrow his was. Gotta be rotary to be useful at that beamwidth on 75M.  You will gain a few tenths, but give up 10db more quickly when off center.

If ya really wanna get some gain, shorten it to 285' and put a set of side by side refelectors behind it. Now youse got f-b and 4-5db more gain. If you're gonna play the game, go for the height and f-b.  Forget the drooping legs cuz you already have enuff room to put up a good gain ant. No need to stretch it out the extra 20' vertically, OM.  Guys do that to get the input impedance and efficency up on a shortened dipole, but not in your case.



T

After doing some modeling JJ, turns out your right....not a substantial drop...bout 1 db if I lop off 20 feet
So tommorow (weather permiting) I will take another stab at it.

Thanks Brent
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« Reply #16 on: December 01, 2005, 05:49:48 PM »

I am bummed JJ, but thanks...I guess I will shorten it. It would be flat and high with the ends dropped down in the vertical plane.  Is it worth it? I hate to shorten it.
B

Naw, shorten it.  The pattern is way to narrow anyway as a double extended zepp. I modeled W2ZM's and he was yellowfied when he found how narrow his was. Gotta be rotary to be useful at that beamwidth on 75M.  You will gain a few tenths, but give up 10db more quickly when off center.

If ya really wanna get some gain, shorten it to 285' and put a set of side by side refelectors behind it. Now youse got f-b and 4-5db more gain. If you're gonna play the game, go for the height and f-b.  Forget the drooping legs cuz you already have enuff room to put up a good gain ant. No need to stretch it out the extra 20' vertically, OM.  Guys do that to get the input impedance and efficency up on a shortened dipole, but not in your case.



T

After doing some modeling JJ, turns out your right....not a substantial drop...bout 1 db if I lop off 20 feet
So tommorow (weather permiting) I will take another stab at it.

Thanks Brent

You mean to tell us it isn't finished yet. Sheesh.
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K1JJ
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« Reply #17 on: December 01, 2005, 06:25:25 PM »

You mean to tell us it isn't finished yet. Sheesh.

So how's YOUR 80' tower/ antenna project going there, SteppIR breath?   Grin Grin Grin

T
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« Reply #18 on: December 01, 2005, 06:42:21 PM »

I'll send you some pictures in about a week.  Wink
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Jim, W5JO
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« Reply #19 on: December 01, 2005, 07:36:14 PM »

Egyptian society went bust with pictures Dave.  Can you read the directions?  I understand it is tough to assemble
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« Reply #20 on: December 01, 2005, 08:00:16 PM »

Egyptian society went bust with pictures Dave.  Can you read the directions?  I understand it is tough to assemble

None of my own stuff has directions or even direction. That's why it's MY stuff.
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WA1GFZ
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« Reply #21 on: December 01, 2005, 10:43:16 PM »

Brent,
It will work fine as long as you get up 250 feet. I found shorter than that is just a bit harder to match.280 or 260 feet will be great!.
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W1IA
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« Reply #22 on: December 02, 2005, 03:31:23 PM »

I am bummed JJ, but thanks...I guess I will shorten it. It would be flat and high with the ends dropped down in the vertical plane.  Is it worth it? I hate to shorten it.
B

Naw, shorten it.  The pattern is way to narrow anyway as a double extended zepp. I modeled W2ZM's and he was yellowfied when he found how narrow his was. Gotta be rotary to be useful at that beamwidth on 75M.  You will gain a few tenths, but give up 10db more quickly when off center.

If ya really wanna get some gain, shorten it to 285' and put a set of side by side refelectors behind it. Now youse got f-b and 4-5db more gain. If you're gonna play the game, go for the height and f-b.  Forget the drooping legs cuz you already have enuff room to put up a good gain ant. No need to stretch it out the extra 20' vertically, OM.  Guys do that to get the input impedance and efficency up on a shortened dipole, but not in your case.



T

Yay!!! Antenna up..285 foot double extended zepp. On 75 till I finish the tunner for 160.
running the big rig at 250 watts through the 250 watt Johnson matchbox.


BTina

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« Reply #23 on: December 02, 2005, 03:44:18 PM »

Great!  That shud work out FB, esp for west coast AM, OM.

Now we can get down in the DX window tonight with your new high gain array. [it's radio whooping time into Eu.... Grin Grin Grin

T
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There's nothing like an old dog.
WA1GFZ
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« Reply #24 on: December 02, 2005, 04:07:12 PM »

I agree height does the most for strapping out RF. My phased array on 75 was lower than the 250 foot dipole. I never worked JAs on the phased array but did on the higher antenna.
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