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Old August 22nd 07, 05:40 PM posted to rec.radio.amateur.antenna
Jim Lux Jim Lux is offline
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First recorded activity by RadioBanter: Mar 2007
Posts: 801
Default Off-center fed dipole, questions

Bob Spooner wrote:
"Jim Lux" wrote in message

...
I doubt there's anything special about the 22 ft. As many have pointed
out, it's a deliberately unbalanced antenna which radiates from both
vertical and horizontal parts (and influenced by the towers, trees, and
buildings nearby), with a nice choke at some point to keep RF from coming
back in the shack on the outside of the coax.
...


If the choke is effective in removing the common mode current, then the
feedline will not radiate very much.

choke at the shack, was my thinking.. I believe that the original intent
of the design was that the feedline could radiate. It's a compromise
antenna of sorts, so one can't be too picky about patterns,
polarization, etc.


I also recall seeing a diagram with choke on the ground, and feedline to
shack laying on ground (which would, of course, tend to reduce any
coupling to it)..


I suppose the real question is whether there is a statistically
significant difference in performance between this and any other random
dipole. If 100 hams put up a Carolina Windom, and 100 hams put up an
OCF dipole of some other sort, and 100 hams put up a multiband dipole,
will the variations within the groups be larger than the variations
between the groups. I suspect they will. For low gain antennas in
random installations, there's so many other factors that influence
pattern and efficiency that I doubt you could accurately measure the
difference.

Probably more important just to get some sort of wire in the air and
somehow get a match so the transmitter doesn't fold back, and not worry
too much.