On 4/28/2016 6:12 AM, jimlux wrote:
Back in the day, a company called Kirk made a series of what they called
"helicoidal" beams. The elements were tapered fiberglass with approx
This idea of a spiraled element has been around for decades. From an
electrical standpoint, it's not a whole lot different than a loading
coil at the base: the radiator being "physically short compared to a
It's actually a combination of bottom and center loading.
However, even though the inductance is uniformly distributed,
the loading effect will be dominated by the turns near the
bottom, thus Jim's comment is basically correct from that
viewpoint. However, the Q of a coil wound of wide strap on
a small diameter is poor. It might seem that the wide
strap would be good for Q, but it is not, for two reasons.
First, the current concentrates at the edges of the strap,
and thus the copper losses are no better than a wire.
Second, the wide strap necessitates a small number of turns
per inch, which reduces turn to turn coupling and lowers
the Q. This design is worse than linear loading, which
is worse than just a good air coil.
A tunable version is shown here:
http://www.force12inc.com/products/tornado-tuner-80d-motor-tune-double-coil-for-80-meter-rotary-dipoles.html
Not cheap though.
Rick N6RK
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