Topband: May 2005 EET article about the DLM

[ac7a@cox.net]

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