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Author Topic: Antenna in the woods  (Read 280 times)
KC8ULE
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Posts: 4




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« on: September 17, 2003, 10:11:00 PM »

I live on a wooded lot.  I appear to be limited to using either a vertical or a 75' tower (too expensive).  Ok; will the trees absorb HF to the extent that the vertical will be useless?
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N6AJR
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Posts: 9910




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« Reply #1 on: September 17, 2003, 10:16:22 PM »

Try a Fan Dipole  ( $10 or so) hanging from the trees, ( do a search here on Elmers Search for fan dipole) and remember any antenna is better than no antenna at all
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K0ZN
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Posts: 1553




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« Reply #2 on: September 17, 2003, 11:22:07 PM »

 
Don't worry about trees on HF, especially the lower bands (160-80-40-30). " a Non event". I suppose on 15 M and above there could be some absorbtion, but I wouldn't get too excited. I am no expert at all on this, but I have heard the kind of trees has some impact, with pine trees being a little worse due to a higher mineral content in the sap and/or trees with a higher level of moisture in the sap. I would think that hardwood trees would be pretty much "invisible" at HF. If they are the kind of trees that loose leaves in the winter, then you would likely see a little attenuation in the months the sap is up. e.g. summer. If you put up a vertical antenna, be SURE to put in a lot of radials...a "lot" starts at about 40. If you only put in a few radials, don't blame the trees for your poor antenna performance! (It isn't the trees; it is the poor ground system!) Personally, I would rather have some trees to hang horizontal antennas from, if they are fairly tall trees. Just make sure you use a good insulated wire for the antenna if it will be touching the trees at any point. You don't want bare wire touching wet trees. I CAN tell you that trees WILL badly absorb an upper frequency VHF or UHF signal. A lot of trees with wet leaves will "eat" a 432 Mhz signal! I have noticed that local 2M FM signals are slightly stronger in the winter when the sap is down and the trees and bushes are "dry", but it is not a big deal and the effect would be far reduced at HF. Bottomline: I wouldn't be concerned at all on any frequency from 17 meters down. On 15 and 10 M you likely will have a little better luck with a horizontal antenna as high as you can get it. Have fun with your antenna project.

73
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N3BIF
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Posts: 1190




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« Reply #3 on: September 18, 2003, 12:03:13 AM »

     You can run insulated wire over,through,around, and under branches , I have with over 25 various antennas but my loop is my favorite( Still havent gotten around to the fan yet AJR,)
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W4TYU
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Posts: 518




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« Reply #4 on: September 18, 2003, 05:14:21 AM »

I am using a all band vertical (Cushcraft R7000) set in the middle of the trees in the back yard.  I have worked all over the globe on CW. SO I say put one up and enjoy. Of course propagation on 15 meters and up is not good at this point in the sun spot cycle.  I use a dipole for 80 meters.

As to using radials, follow the manufacturers instructions. My antenna did not require radials and I am not using any.

Ole man JEAN
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KB0ETC
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Posts: 248




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« Reply #5 on: September 18, 2003, 08:19:50 AM »

How about a large horizontal loop running around your lot.  All you need is a balun and tuner (feed with ladder line), and you have a very respectable multi band HF antenna.
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KE4SKY
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Posts: 1045


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« Reply #6 on: September 18, 2003, 09:46:14 AM »

Make a fan dipole of insulated wire, find some antique window sash weights at garage sales to weight the ends, but allow them to move. Raise center feedpoint connector on 5/16" Dacron with pulley so that the antenna can give in the wind when the trees sway.

If you don't want to make your own fan dipole, you can get a very sturdy one ready-make, cut to your freqs from NI4L in North Carolina.  His are hurricane proven.  I have three of his at various locations.
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KT8K
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Posts: 1490




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« Reply #7 on: September 18, 2003, 02:43:00 PM »

If your trees are tall enough you can make vertical dipole(s).  Then you won't need to run radials and worry about ground systems and associated losses.

The loop is definitely a good idea, and I expect to be putting up one of my own soon.  Reports are that loop impedances (for bands where it's 1 wavelength or longer)are frequently in the 100 ohm range - easy to match and will work well with simple coax cable.  Maybe a 1:1 balun at the feedpoint (can be a choke balun made from 20 x 6" turns of coax taped together) would stop feedline radiation and help performance, too.

I am looking around for a new house, and tall trees are a big plus.  (Who needs steenkeeng expensive towers?  I don't want to climb (or pay for) no steekeeng towers!)  A good slingshot and fishing pole to feed out some line, and you can string wires all over the place.
Good reception & hope to hear you on the air.
73 de kt8k - Tim
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WB6BYU
Member

Posts: 13342




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« Reply #8 on: September 18, 2003, 03:45:00 PM »

On HF this isn't a problem - I'd string some wires in
the trees and enjoy it!

On 2m you may have some attenuation, so getting above
the trees could be important for serious weak signal
work, but not for hitting the local repeaters.

The next question is, what type of trees are they?
Pines and other fairly straight conifers can make good
75' towers if you trim the top and attach your antenna
as though it were the top of a telephone pole.  (But
don't try anything TOO tall - trees whip back and forth
in the wind a lot more than steel towers do!)  However
oaks and other broadleaf trees aren't as suitable as
towers because of their more branched shape.
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