For years I have been beating the drum for the benefits associated with
building a wire cage around a grounded tower as a convenient and more
efficient method of obtaining an effective top band vertical. I
recommended this type of feed (called folded unipole) for many radio
station customers over the years promising improved efficiency, better
bandwidth, lower ground losses, and good lightning protection and so
on. Proponents even went so far as claiming that the unipole can
operate better without radials than the conventional series fed
broadcast antenna. Well based on a paper presented at a recent NAB
convention several BC design engineers have blown away those claims.
There is one small caveat. The presenters work for Kintronics, the only
active US manufacturer today of BC antenna couplers. (A folded unipole
if properly adjusted would allow for direct feed by proper adjustment
of the tower tap from the skirt theoretically eliminating the need for
the expensive Kintronics coupler with modern transmitter with band pass
filters.) Yet keeping all that in mind the paper presents a convincing
arguement that a skirt may for many be a waste of time. Have a look at
the tests and arguments and let me know what you think. The paper is
available for download at:
http:www.dlr.com/dlrweb/papers/nabpaper/Nabpaper.htm
73
Herb, KV4FZ
St. Croix, VI
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