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U dipoles
In article ,
Ralph Mowery wrote: I have seen many plots of inverted V and flat top dipoles, but none of a V or U shaped one. That is like one I have up for 80 meters. I have two trees that are about 20 feet short of the distance I need for an 80 meter dipole. The trees are so that I can get the wire up about 60 to 70 feet on the ends and the middle is only about 35 to 40 feet above ground. Here's a different suggestion. Put up as long a section (horizontal except for the sag) as you can between the two trees. Say you can get 115 ft that way. Then extend each end 10 ft by adding a vertical wire dropping down. Now the high current point on 80 m is way up in the air where it will do the most good and the antenna won't be as much of a cloud-warmer as your non-inverted V would have been. Yet another suggestion: Just put what you can up there between the two trees. So it's 20 ft or so short. Feed it with home-made open wire (second choice: ladder-line). Use a good tuner. The main problem with antennas slightly short of a half-wave long is that they have relatively low resistance and appreciable capacitive reactance so feedline losses go up. But if you use really low loss feedline they can still be pretty good. For use on harmonics there is some advantage to avoiding an actual half-wave on 80 m since that will have very high impedance on even harmonics and with some feedline lengths can be very hard to match. David VE7EZM and AF7BZ -- David Ryeburn To send e-mail, change "netz" to "net" |
#3
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U dipoles
Ralph Mowery wrote:
In article david_ryeburn-9073AE.11364031082016@88-209-239- 213.giganet.hu, says... Here's a different suggestion. Put up as long a section (horizontal except for the sag) as you can between the two trees. Say you can get 115 ft that way. Then extend each end 10 ft by adding a vertical wire dropping down. Now the high current point on 80 m is way up in the air where it will do the most good and the antenna won't be as much of a cloud-warmer as your non-inverted V would have been. Yet another suggestion: Just put what you can up there between the two trees. So it's 20 ft or so short. Feed it with home-made open wire (second choice: ladder-line). Use a good tuner. The main problem with antennas slightly short of a half-wave long is that they have relatively low resistance and appreciable capacitive reactance so feedline losses go up. But if you use really low loss feedline they can still be pretty good. For use on harmonics there is some advantage to avoiding an actual half-wave on 80 m since that will have very high impedance on even harmonics and with some feedline lengths can be very hard to match. David VE7EZM and AF7BZ Thanks for all the ideas. That is not the only antenna I have for the low bands. I do have a 60 foot tower and triband on it. Also an off center fed antenna in another directionthat is long enough to be almost flat. If one of the ropes had not grown into the tree, I might be tempted to try loading it near the end, but I can not get that end down now. Most of my work on 80 meters is just some friends in the state and not not much DX so the cloud warmer is really to my advantage on 80. I was just courious as to what patern it may be for that U or V shaped antenna as I don't recall seeing a computer plot of one. Just the flat top and inverted V antennas. --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus In free space, and inverted V and an inverted inverted V have the same characteristics. The issue here is that the center is close to ground which will have a big effect on the pattern. -- Jim Pennino |
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