Correcting an address typo on the NAB paper concerning folded unipoles
vs. a series fed vertical, instead see:
http://www.dlr.com/dlrweb/papers/nabpaper/Nabpaper.htm
I recommend reading it!
I am a little perplexed by the following quote:
These results reveal that the field strength was not diminished
significantly by going from 120 to 30 radials for any of the four
antennas.
Perhaps I was missing something...
For those looking for just a quick report, below is the conclusion
summary in their report:
CONCLUSIONS
No major differences in field strength between the folded unipole and
series-fed test cases were found for any of the configurations tested.
The folded unipole was not found to have a significantly better
radiation efficiency than the series-fed for a given tower height and
ground system. The ground currents for the folded unipole are found to
be approximately equivalent to those for a series-fed tower despite the
unipole's lower driving point current, which results from a higher input
resistance. No major differences in bandwidth were found between the
folded unipole and series-fed tower when sideband VSWR was observed
rather than simply input resistance. Furthermore, with the wire cage
connected to the tower at the top and bottom, the antenna was found to
have even wider bandwidth than for either the standard series-fed or
unipole skirt-fed tower.
The NEC-4.1 models of the various antenna and ground system configura-
tions were found to give results that are in good agreement with
measurements. The computer modeling was shown to be a valuable design
and research tool allowing investigation of a variety of antenna systems
that could not otherwise be studied in an economical way. The need for
a good ground system has been confirmed by both measured and modeled
results. The modeling also agreed with measurements in that series-fed
and folded unipole antennas don't differ significantly in radiation
efficiency for a given tower height and ground system. Field intensity
differences between the folded unipole and the series-fed antenna of
less than 9% were consistently computed as well as measured.
From: AN EFFICIENCY COMPARISON: AM/MEDIUM WAVE
SERIES-FED VS. SKIRT-FED RADIATORS
By: Ronald D. Rackley, P.E. - du Treil, Lundin & Rackley, Inc.
Bobby L. Cox, PhDEE - Kintronics
James R. Moser, MSEE - Kintronics
Tom F. King, MSEE - Kintronics
73, Bill K0HA
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