Posted by
John Magliacane on
Jan 08, 2008; 3:28pm
URL: http://elecraft.85.s1.nabble.com/dipole-antenna-efficiency-tp458071p458085.html
> John Magliacane wrote:
>
> > It's a traveling wave antenna where the helix is wound around a
> > supporting vertical mast that serves as a reflector.
David Woolley <
[hidden email]> wrote:
> None of the references I found (including university course
> notes), when researching this at the weekend, described anything
> other than a dielectric core. They did suggest a spectrum of
> behaviour from basically linear polarized, to circular polarized,
> depending on the pitch.
Johnson's "Antenna Engineering Handbook" (McGraw-Hill) among others
describes the antenna design to which I am referring. A preview of
chapter 28 where the antenna is described is available at:
http://books.google.com/books?id=xTSNJhVlHGgC&pg=PP1&sig=qdNrli_UaJsiZB_gq3cRqvjy4DY#PPT961,M1Dielectric Communications (formerly RCA) manufactures such an antenna
(model TCL) for the purpose I originally described. Their older
print catalog describes the antenna in more detail than what is
available on the web:
http://www.dielectric.com/broadcast/images/tcl1.jpghttp://www.dielectric.com/broadcast/vhf.aspJampro does a better job of describing and illustrating the antenna
on-line. In particular, they state:
"The JTC Circularly Polarized Spiral Antenna consists of a supporting
pole around which are multiple stainless steel spirals wound at
specific pitch angles and spaced from the pipe by heavy-duty
fiberglass-reinforced low-loss insulators. The array acts as a
traveling wave antenna, with the main beam broadside to the support
pole and exceptionally low radiation along the axis of the pole. It
produces an omni-directional azimuth pattern with low VSWR."
Full description and photos are available here:
http://www.jampro.com/index.php?page=jtc-circularly-polarized-spiral-tv-antenna73, de John, KD2BD
Visit John on the Web at:
http://kd2bd.ham.org/.
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