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Wes, N7WS wrote:
"Could you describe in more detail what the "pictures" are saying." My edition of "Low-Band DXing" is copyrighted in 1994. The "pictures" are graphs of current distribution on (6) different 1/4-wave vertical antennas: 1) full size 2) base loaded 1/8-wave of wire 3) capacitive hat loaded 1/8-wave 4) center loaded 1/16-wave wire above & below 5) continuously loaded (all coil) antenna 6) combined top and base loading of short vertical The current distribution graphs are in a section (2.1) titled "Radiation Resistance" In every case , the current tapers lower from feedpoint end to the loading coil`s end nearer the open end of the antenna. Devoldere discusses the various loading methods. Devoldere says the full size 1/4-wave vertical has a radiation resistance of 36.6 ohms. His 50% length base loaded example has a radiation resistance of 6.28 ohms. His top loaded example has a radiation resistance of 18.3 ohms. His center loaded example has a radiation resistance of 22.1 ohms Radiation resistance is our goal. Radiation resistance versus total resistance (radiation+loss resistances) is the antenna efficiency. The all coil antenna has a calculated radiation resistance of 16.4 ohms. The point is that all loading coils show less current at the top than at the bottom because that`s the way it is, superposition. Now that we`ve been re-Bushed, I`ve had time to answer Wes` question. Best regards, Richard Harrison, KB5WZI |
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