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Bassbug
| | Posted on Sunday, July 28, 2002 - 1:37 pm: | 
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307, I have a question. Is there a way to make a 5/8 wave dipole antenna? The best to my knowledge 1/2 wave is the most for a horizontal dipole. I'm wanting to put up a center fed dipole with nine foot on each end. Is there any way to make a 5/8 length? Any imput would be appreciated. Thanks. Eddie |
Marconi
| | Posted on Sunday, July 28, 2002 - 11:47 pm: |
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BassBug if you want to make an antenna with a longer wavelength radiator, build you a wire loop and then you can maintain the symetrical pattern on the flat side that a 1/2 wave dipole or yagi would give you.
A dipole with a radiator longer than a 1/2 wave length looses the traditional figure 8 pattern we have all come to know. This longer radiator will not radiate best to the broadside of the wire like you may think. It will likely produce a pattern with numerous RF peaks and nulls that run tangent and more or less in the directions towards the ends of the wire. It will work a little like a long wire.
As an example, you could have two stations out in the distance and more or less in the direction of your wire, where both are about the same distance from your station, but where they are maybe a couple of clicks apart, and you might hear one very well and the other not at all. This could happen where one falls in a peak and the other falls into a null. This also assumes that everyone is on a flat wire pointed in the right direction.
This is not to say anything about the problems you will have matching and tuning such a long dipole.
This is why all rotatable beams you see are built on a version of a 1/2 wave dipole or the full wave in the case of a wire loop. They are able to maintain pattern symmetry so that directors can work to increase the directional quality needed.
Marconi |
Bassbug
| | Posted on Tuesday, July 30, 2002 - 8:44 pm: |
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Thanks, Marconi for your input into the 5/8 wave dipole. RIght now im running an imax 2000 vertical ground plane. I was just looking for a way to increase the gain on a horizontal dipole. I pretty much thought, that a half wave was the most that could be gained for a center feed wire. I was looking for a good home brew that I could go to the flat side with. I have local operators that run s vertical ground planes that just tear me up on recieve. I know that the horizontal quiets things down alot for skip and DX. Im going to use a 1:1 Balun on my dipole. I feel that the balun would balance the coax for the antenna. Thanks again 73's Eddie |
Highlander
| | Posted on Wednesday, July 31, 2002 - 9:14 am: |
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Try looking up an "extended double zepp" antenna. It is like a dipole, but longer legs.... |
Marconi
| | Posted on Wednesday, July 31, 2002 - 12:46 pm: |
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Bassbug there is a simple way to get a clue to see if you may need a balun. Use a simple portable field strength meter near the line or at your station. If the meter is reactive (hot), an effective balun might help. If you don't show RF on the line, then I doubt a balun will help anything.
The big thing a balun can do, if it works right, is to help decouple the line from the antenna at the feed point and help improve symmerty of the dipole pattern. This allows the flat dipole to really work like a horizontal should, and this makes for deeper nulls at the ends of the wires. This produces a better figure 8 pattern, so-to-speak.
If you have RF on the line, the line will probably come into play as a vertical radiator. This will basically be about the same as tilting the wire from a true 180 degrees towards the vertical. In this case, just a little variation can be significant. Doing so, changes the symmetry in the antenna. So all this work may be for nought if your not good and flat.
If your bleeding neighbors are sending out true vertical RF signals, and your coax is hot, then your flat side antenna will probably not produce up to your expections because the unwanted signals are getting to your RX via your coax line.
If your neighbors vertical antennas are sending out a lot of horizontal signal along with the vertical RF, as some verticals can do, and your line is hot or not or even if you have a good balun installed, you may be surprised that the interference may still be there.
In all cases, if you can lay your wire with the ends pointed in the direction of the offending stations and your wire is good and flat, you will have the best shot at success.
You might also consider a rotatable dipole and then you could have more control over the offending station.
Good luck.
Marconi |
Bassbug
| | Posted on Wednesday, July 31, 2002 - 4:55 pm: |
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Thanks Marconi, Take care. |
Bassbug
| | Posted on Thursday, August 01, 2002 - 5:24 am: |
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Hay, Highlander. I did a serch on the net. on the Extended Double Zepp antenna. Its got extended legs of 0.64 wave length. And a ledder line of 450 ohm. I found a online calculator. For 27 mhz a ledder line of five foot on a 1:1 balun to 50 ohm coax. This is a center fed dipole. Each leg is 23.3 long. The word Zep is short for Zeppelin. The ham sites is loaded with this antenna. This Antenna came about with the hams at the second world's war. Thanks Highlander. |
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