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I just completed the installation and tuning of a multiband inverted vee for
160, 80, and 75 meters. Essentially, the antenna consists of a center PVC insulator with 6 terminal posts (2 per band) and the three dipoles separated by wooden dowel-rod spreaders at spacings of about 6 inches. All three sets of wires are direct fed with one RG/8u. I have adjusted the lengths of each antenna to move the resonant point to preferred frequencies for each band: 1.825 on 160, 3.525 on 80, and 3.775 on 75. However, at resonance the SWR on all antennas remains relatively high -- an MFJ259 analyzer says resonant SWRs are around 1.7-2.0:1 and characteristic impedances are 100 ohms or slightly higher. Is a 2:1 balun the solution, and which balun method? Seems to me I have the following choices: 1. A "balun kit" from someone like thewireman.com and build my own. This could be in either the form of a voltage or a current type -- which type would be best? 2. A coax balun in the form of a 1/4 wavelength of RGB/11u 75 ohm coax -- replacing a portion of the RG/8u feedline with RG/11u. But since I am using this for two bands... what length would offer the best compromise for both 80 and 160? 3. A coiled-coax balun which I have seen described as "about 16 turns of RG8x on 3 inch PVC stock". All of these options are easily do-able, but which looks like the best route? Your opinions are welcome. ------ -larry K8UT |
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