[Elecraft] dipole antenna efficiency

[John Magliacane]

> 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 <forums at david-woolley.me.uk> 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,M1

Dielectric 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.jpg
http://www.dielectric.com/broadcast/vhf.asp

Jampro 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-antenna


73, de John, KD2BD


Visit John on the Web at:

	http://kd2bd.ham.org/
.
.
.
.


      ____________________________________________________________________________________
Be a better friend, newshound, and 
know-it-all with Yahoo! Mobile.  Try it now.  http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ