Folks,
At the risk of stirring up a hornets' nest ......
.... I continue to see claims that the Double Bazooka exhibits a wider
VSWR bandwidth than the equivalent thickness half-wave dipole. But I
thought that W2DU had showed conclusively that the "reactance
cancellation" mechanism claimed for the DB was a fallacy, and that AI1H
(ex-W1DTY) had showed that the real explanation for any bandwidth
increase was losses in the coaxial elements. In other words, the same
effect as putting a resistor across the feedpoint!
Am I missing something? Is there subsequent work that has proved W2DU
and AI1H wrong? Or do folks just like using unnecessarily-complex, lossy
antennas :)
I have an interest in the topic because I just did some related
experimental and modelling work on using coaxial elements to "shrink"
the size of a HexBeam. Yes, you get the expected "velocity factor" size
reduction, but you also get unacceptable losses introduce by the coaxial
stubs. A HexBeam driver constructed of RG58 would exhibit coax losses of
about 13dB. If you're interested you can read about it at:
http://www.karinya.net/g3txq/coax_antennas/
I know my test configuration was different from the DB, and that DB
losses will not be of the same order, but the message is the same:
"quarter-wave inductive coaxial stubs are lossy, low-Q, elements."
Now I think I'll turn off the computer for a few days until the hostile
reaction dies down :)
73,
Steve G3TXQ
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