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#1
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Antenna too long??
I am trying to put up a dipole for 40 m. The formula calls for about 65
feet. Between my tress I easily have space for twice that. That would still resonate, would it not. Tell me that longer is better, at least when it comes in multiples. 73 Uwe |
#2
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66 feet 4 inches drops you in the middle of 40 metre band.
33 feet 2 inch a leg. Between trees is better than through them. Re check everything, when the leaves are on the trees. QRP HomeBuilder web site is at http://qrp.pops.net/qrp/default.htm They have dipole antenna software for free. Best of luck |
#3
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Uwe, 'Bigger/longer' isn't necessarily 'better'! A longer dipole -may- resonante on the desired frequency, but the 65 feet (approximate) is really all you need. Twice that length would probably work for you, but feeding it in the center would also be a very bad impedance match for 50 ohm coax. Not to mention will produce a radiation pattern different from what you might expect. A full wave, instead of a 1/2 wave, dipole can be made to work, but all things considered, why bother? 'Doc |
#4
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On Thu, 15 Apr 2004 06:31:41 -0500, 'Doc wrote:
Not to mention will produce a radiation pattern different from what you might expect. Oh, and just how different would the pattern be? Danny, K6MHE |
#5
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Dan Richardson wrote:
On Thu, 15 Apr 2004 06:31:41 -0500, 'Doc wrote: Not to mention will produce a radiation pattern different from what you might expect. Oh, and just how different would the pattern be? A one-wavelength dipole has about 2 dB gain over a 1/2WL dipole at the expense of other directions assuming a height of 1/2WL+. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
#6
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Dan, It's green instead of the 'normal' blue... 'Doc |
#7
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On Thu, 15 Apr 2004 17:39:32 -0500, 'Doc wrote:
Dan, It's green instead of the 'normal' blue... 'Doc I fail to see that answers my question. Which was and is just how is the pattern of a ½-wave dipole different than a full-wave dipole? I know the answer, base upon you response to the original question I wonder if you do. However, because of you refusal to include the portion of the previous message that you responding too in your postings (normal N/G etiquette) it is difficult to be sure what you are talking about. Danny |
#8
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"Dan Richardson @mendolink.com" ChangeThisToCallSign wrote in message ... On Thu, 15 Apr 2004 17:39:32 -0500, 'Doc wrote: However, because of you refusal to include the portion of the previous message that you responding too in your postings (normal N/G etiquette) it is difficult to be sure what you are talking about. He claims he doesn't know how to quote. I plonked him some time ago. Got tired of trying to figure out what he was responding to. Would rather have not done that as he does have useful information but his posting method is just to cryptic. |
#9
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"'Doc" wrote in message ... Uwe, 'Bigger/longer' isn't necessarily 'better'! A longer dipole -may- resonante on the desired frequency, but the 65 feet (approximate) is really all you need. Twice that length would probably work for you, but feeding it in the center would also be a very bad impedance match for 50 ohm coax. The impedance will still be 50-to-70 ohms if you add the extra half-wavelength to just one end of the antenna. i.e. The wire on one side of the antenna feed point (coax connection) is still 32.5 feet, and the wire on the other side would be 65' + 32.5' plus another 3.3', since there is no end-effect on the extra half-wavelength of wire you are adding. So actually, one side is 32.5 feet and the other side is 100.8 feet. You should get almost 2 db of gain in four directions (a "cloverleaf") by doing that. You will also get a significant reduction in signal strength (a "null") broadside to the antenna and off the ends. I used a dipole like that for years in Florida where one of the gain lobes was NE and the nulls cut out a lot of the stateside QRM for me during European contests. The full-wave dipole was up about a half-wavelength (65 feet), so I used RG59 (75 ohm) coax instead of RG58 (50 ohm) coax, and had a good match. No balun was needed. Andy |
#10
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King Zulu wrote:
The impedance will still be 50-to-70 ohms if you add the extra half-wavelength to just one end of the antenna. Actually, it may be closer to 100 ohms. It's an OCF somewhat like a "Windom" fed with two-conductor transmission line. The "Windom" is supposed to have a feedpoint around 300 ohms. i.e. The wire on one side of the antenna feed point (coax connection) is still 32.5 feet, and the wire on the other side would be 65' + 32.5' plus another 3.3', since there is no end-effect on the extra half-wavelength of wire you are adding. It's an interesting OCF antenna but probably subject to common mode currents unless an excellent choke is used at the feedpoint. You should get almost 2 db of gain in four directions (a "cloverleaf") by doing that. Since it's a one-wavelength antenna, it won't quite achieve a cloverleaf pattern. It's about the same gain as a 1/2WL dipole (6 dBi) but with a much wider horizontal beamwidth. For a 130 ft. long antenna, the cloverleaf pattern develops around 10 MHz. -- 73, Cecil, W5DXP -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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