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Old November 4th 04, 02:08 PM
Richard Harrison
 
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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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