Hi,
I am just returning to the list after being off for a few months so this horse
may have already been beat to death.
The tech magazines at work make the rounds over time and I sometimes don?t see
them until they are few months old. Yesterday, my boss dropped an EE Times
article on my desk regarding the U of RI DLM antenna. Yes, we?ve all seen the
original articles about a year or so ago, but this one was from May of this
year.
The article was titled ?Tweak to inductive loading shrinks antenna.? Nothing
new about the subject to us, but what was new to me is that the antenna had
been independently tested at the Naval Undersea Warfare Center antenna range on
Fishers Island, NY.
The test antenna was a 7MHz monopole, 50% of the normal quarter-wave size. Now
one thing from an illustration that begs more information was the ground
system. It shows 150? radials, which appear to terminate at the sea water?s
edge. There is about a mile of seawater between the test antenna and the
calibrated receive antenna.
The article concludes; ?Vincent?s antenna designs were tested using the
official regime the Navy uses to certify antennas. Vincent?s Plano Spiral Top
Hat antenna, at 7MHz, was shown to have equal sensitivity to a normal
quarter-wave antenna but at 50% the quarter-wave unit?s size. In addition,
bandwidth of the Vincent design was nearly twice as wide as that of the
quarter-wave unit.?
I have studied the DLM information at the U of RI website and have tried using
EZNEC to model the antenna on 160 meters. When it was all said and done I
wasn?t able to get the antenna to resonate anywhere near the model frequency.
It could be that I didn?t accurately model the helical section. From the
modeling I did complete it didn?t appear anything out of the ordinary was
occurring with the design. All of the losses I had added to the model were
eating away at the efficiency.
Even though I would love to believe that the DLM is for real, I am still having
trouble accepting the claims and now the Navy?s test results.
I guess that is the curse of being named ?Thomas.?
Regards, Thomas ? AC7A
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