Jim,
I put up a short vertical dipole for 40M. It is 25' tall and has top and
bottom X-shaped capacitive hats that are 42.5" square with a perimeter wire
attached. The lower capacitive hat is about 6' above the ground.
While the antenna is resonant just under 9 mHz, it works very well on both
30M and 40M. My "go-to" antenna on 40M is Double Zepp about 90' on a
side. I frankly did not expect this short vertical dipole to be competitive
with the DZ, yet it was! As expected, close-in reports on the Reverse Beacon
Network favored the DZ, but there were many distant stations that reported
in on the Vertical Dipole that weren't reported on the DZ.
I've compiled about 10 pages of RBN comparisons of the two antennas, and
overall, there is less than a dB difference between the two antennas on
common RBN sites, with an advantage to the Vertical Dipole on longer DX.
Daytime favors the DZ, nightime the Vertical Dipole.
While this is not rigorous science, I am satisfied that I can generally
replicate the performance of a very successful antenna with a much larger
footprint with the much smaller Vertical Dipole. Mine is a wire version hung
from a tree and can be deployed
in about 10 minutes. I'm going to increase the size of the hats to make
this antenna resonant on 40M and would expect even better results. This
antenna can be very easily fabricated, I'd like to encourage results from
anyone trying something similar.
Paul, K5AF
In a message dated 9/20/2012 11:00:18 P.M. Central Daylight Time,
wa3mej@comcast.net writes:
I noticed that some of the DXpeditions are using vertical diipoles next to
the sea on at least some of the higher bands ( I am guessing 20 and up).
I stuffed the data into EZNEC 5.0 and came up with some suprising results,
hope I did it correctly I am not an antenna guru . Now as Tom has just
indicated modeling is great but its only modeling it doesnt really tell what
happens in the real world/ground conditions etc.
Does anyone have any real world experience with these dipoles? Do they
work in non beach environments such as near the mountians? Comments
welcome... and I am willing to take the comments off list if it suits you.
If this is not a fools folley I will put together what I find suprising
and put it on my web site for everyone to access but I dont to take the time
to document it if its a waste of time.
Jim
http://www.qsl.net/wa3mej/index.htm
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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