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#1
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Unequal dipole legs on shortened antenna
I have a shortened all-band dipole with two loading coils on each leg.
On 80 and 160 it has a very narrow resonance bandwidth that requires a choice between data (low end) and phone (hi end). I am using a wide-range manual tuner. By changing the length of two segments on each side, I can move the resonant "passband" where I want it on 80 and 160. Using the antenna outside the passband results in unacceptably huge (like 99%) feedline losses -- when the feedline is coax. I suspect that if I shift to ladderline, the losses will just move to my tuner. What would happen if I adjust one leg for resonance on phone and the other for resonance on data? If this would give me 50% of the resonant signal of a balanced antenna, that would be acceptable. Ken KC2JDY Ken (to reply via email remove "zz" from address) |
#2
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Hi Ken -
You have a couple of wrong ideas. One relates to the feedline losses. At the frequencies in question, it is extremely unlikely that they could reach 99%--even with some SWR--unless your line is bad, or your antenna is in the next county. Also, your half-wave resonance is deter- mined by the TOTAL length, not by each side independently. So your unequal sides should produce just a single resonance (per band), but with an off-center feed. There's nothing wrong with off-center feed, though. Some folks (including yours truly) have found that off-center feed can be a very useful technique for improving the match--especially if the antenna is in an asymmetrical environment, and/or too low (like mine). BTW, I move up and down in the 80m band using plug-in stubs to change the overall length. Works FB. Good luck with your tuning, and 73, Ed "Ken" wrote in message ... I have a shortened all-band dipole with two loading coils on each leg. On 80 and 160 it has a very narrow resonance bandwidth that requires a choice between data (low end) and phone (hi end). I am using a wide-range manual tuner. By changing the length of two segments on each side, I can move the resonant "passband" where I want it on 80 and 160. Using the antenna outside the passband results in unacceptably huge (like 99%) feedline losses -- when the feedline is coax. I suspect that if I shift to ladderline, the losses will just move to my tuner. What would happen if I adjust one leg for resonance on phone and the other for resonance on data? If this would give me 50% of the resonant signal of a balanced antenna, that would be acceptable. Ken KC2JDY Ken (to reply via email remove "zz" from address) |
#3
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Ken wrote:
Using the antenna outside the passband results in unacceptably huge (like 99%) feedline losses -- when the feedline is coax. I suspect that if I shift to ladderline, the losses will just move to my tuner. Not necessarily. Since a ladderline with an SWR transforms impedances simply have it transform the impedance to something that is acceptable to your tuner. That's what I do. What would happen if I adjust one leg for resonance on phone and the other for resonance on data? Your antenna would resonate half way between phone and data. Maybe not a bad idea. Try it and see if the SWR is still unacceptable. If this would give me 50% of the resonant signal of a balanced antenna, that would be acceptable. Measure the SWR and calculate the losses to see if they are acceptable. -- 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! =----- |
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