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Author Topic: Trees are too close for the wire antenna  (Read 3710 times)
N4MJG
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« on: September 26, 2011, 03:33:53 PM »

 my Swr is going nuts the wires are not suppost to touch trees that what cause swr go up it was ok there for awhile then goes up it don't matter if is raining or dry ! i count 28 step at front and backyard i count 67 step.

The atenna i have now is windom first atenna was G5RV now it went up so is the windom atenna it make sence touching the trees cause swr to go up !  i was about to go with vert antenna my tower is about 40 ft. i have small lot not quite room for it !! Sad up front yard is traffic go by too many house sit side by side ! i like doing 80 meters and other frq. i get on now since with swr keep go up! i get very upset i cant even get on hf !! Sad


73
Jackie
N4MJG
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WB2WIK
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« Reply #1 on: September 26, 2011, 03:48:07 PM »

That was difficult to follow.

However I've never found trees to have much effect on HF antennas, at all.

Most of the wire antennas I've installed over 46 years in ham radio have run through tree limbs and branches, often touching them, and they tuned and worked fine.

If you find wires touching trees is changing your SWR a lot, I have a feeling you have a loose connection somewhere.
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N4NYY
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« Reply #2 on: September 26, 2011, 04:46:30 PM »

Amen. Unless you are running VHF, I would not worry.
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N4JTE
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« Reply #3 on: September 26, 2011, 04:50:19 PM »

HUH ?
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AC5UP
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« Reply #4 on: September 26, 2011, 05:02:44 PM »

my Swr is going nuts

Squirrels! You have squirrels!

Of course your SWR is going nuts, the squirrels are stocking their winter stash by dragging their nuts across your antenna wire. Sure, a few nuts now and then won't hurt anything, but if you had 10 squirrels working the tree while you're trying to work The Coaxial Islands that could be maybe 20 nuts on the wire at any given time.

What you need is a good Bobcat or some MFJ squirrel repellent. I hear it's not in the catalog, but if you give them a call and ask...........
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W8JI
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« Reply #5 on: September 26, 2011, 05:13:55 PM »

I cannot clearly understand your post, but if a wire at the voltage touches branches it certainly can make the SWR change. That might not be the problem, or it might.

Because an SWR change does not happen in some cases does not mean it will not change things in all cases. The end impedance of an antenna can be many thousands of ohms. I've seen it change from wet ropes and wet strings, as well as branches. I've even had open wire line set a branch on fire.   

As a matter of fact a Pecan tree near a 160 vertical in my 160 4 square was changing the impeadace a little bit, even though it was not touching at all.


This idea trees don't ever affect things is just not true.
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N4NYY
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« Reply #6 on: September 26, 2011, 05:46:26 PM »

Quote
HUH ?

You know what, I am thinking of my verticals. They seem unaffected by trees, or at least the last time I measured them.

I am about to remove one for a dipole. I guess I will find out soon enough.
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WB2WIK
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« Reply #7 on: September 26, 2011, 06:36:22 PM »

Tom, of course proximity to almost anything at high voltage points detunes an antenna. 

But in general, you can run wires through trees with very little effect most of the time.

I've had end insulators catch on fire when it's raining; that can certainly happen, but it's not the norm.

The commercially built OCFDs I've seen all use insulated wire, which helps protect them (a bit).  Maybe not against high power, but with 100W they're probably fairly well protected.

I set fire to a tree twice running a kilowatt on 80m when the ends of the inverted vee were right in a tree. Tongue  But moving the ends away from  the tree resolved that. Smiley
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N4NYY
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« Reply #8 on: September 26, 2011, 06:43:50 PM »

Quote
I set fire to a tree twice running a kilowatt on 80m when the ends of the inverted vee were right in a tree.

This is a tease. Don't ever post this unless you have video!   Cheesy Cheesy Cheesy Cheesy Cheesy Cheesy Cheesy Cheesy Cheesy
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N4MJG
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« Reply #9 on: September 26, 2011, 08:12:25 PM »

The antenna is about 30 to 35 ft off the ground ! not sure why the swr is high i even wait to go down never did go down on swr why always high make no sence to me.

We are waiting for guys come up our house trim up the backyard tree ! i will wait and see how effect the swr both antenna are ok ,just not sure why the swr is high cannot fiqure that out Undecided 

Only time will tell maybe i souldn't be worry ! whos know !! thanks for helping me out !

73
Jackie
N4MJG
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KD8MJR
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« Reply #10 on: September 26, 2011, 10:45:23 PM »

The SWR on My G5RV on 20M is 1.6:1 when the Tree underneath it are about 8 inches from the Antenna, on rainy days that goes up to near 1.8:1
Once a year I trim 4 feet off the top of the trees and the SWR drops to 1.45:1 and rain makes no difference. (That's using an LP-100 meter for the readings.)
So IMO tree's do make a difference.

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NO2A
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« Reply #11 on: September 26, 2011, 11:08:42 PM »

I say your swr was never right from the start. Since you have a tower why not put the feedpoint at a high point on the tower and run the ends down as an inverted vee? Where the feedpoint meets the antenna is always a critical point for a dipole. If something is wrong it`s probably there.
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W8JI
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« Reply #12 on: September 27, 2011, 02:56:23 AM »

Maybe a feline is taped to a tower leg, the ladder line is.
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VE3FMC
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« Reply #13 on: September 27, 2011, 05:29:32 AM »

I have dipoles through trees and have no issues with the SWR going up and down. However I use insulated wire for my dipoles. At one time one leg of my 80 meter dipole was touching a big branch on a maple tree and that did not have any effect on the SWR.

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AA4HA
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« Reply #14 on: September 27, 2011, 07:20:49 AM »

Remember that with a Windom (OCF) antenna the balun you are using may need to be a different ratio depending upon how high up you have it mounted;
25-50 feet    4:1 balun
50-65 feet    5:1 balun
65-75 feet    6:1 balun

http://www.packetradio.com/windom.htm

You can elect to ignore the Buxcomm propaganda and just read the article for the technical content.

---------------------
On a small lot you may not be able to "get" 80 meters to work and would need to use a shorter OCF (Windom) that does not work at 80 meters. You really do need the length to run the wires out to their full length. There are designs out there for OCF's that work on the higher frequencies like 40 to 10 meters.

Tisha Hayes, AA4HA
« Last Edit: September 27, 2011, 07:37:30 AM by AA4HA » Logged

Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
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