NEC-LIST:Terminated folded dipoles

I have been experimenting with terminated folded dipoles for some years now
using various dimensions and terminations. I found impirically that a folded
dipole roughly 40% lambda at the lowest operating frequency terminated with
about 1000 ohms and fed with 16:1 balun from a 50 ohm source gave me a VSWR of
less than 2:1 over a range from the lowest frequency to 30MHz.

Efficiences reported by NEC-2 range from 12% to 40% depending on frequency.
Radiation patterns are as one would expect from a doublet of the same length.

 I have experimented with all the so called critical dimensions in length and
spacing and found that they were not really critical at all. Recently I have
simulated all sorts of dimensions, in various configurations from flat tops to
slopers and inverted Vees, and can honestly say that it is a most forgiving
antenna. I have looked at the designs of W3HH and patent of Elmer Bush and
find that their dimensions need not be duplicated to get satisfactory
performance. In general signals are about 3 to 6dB below a resonant dipole at
the same height on all the HF amateur bands.

Does anyone have any experience and am I missing something here? I would be
pleased to provide source files to anyone who wants to experiment.

PS. The July Edition of Radcom (the RSGB journal) carries a short summary of
some of the background.

Chris Turner
G4HKP/ZS6GM

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