[TowerTalk] VHF antenna orientation

[L. B. Cebik]

> Here's an easy one. I am about to install a 10-ft vertical antenna for
> 2-meters. If I were to install it at the top of my tower, it would
> interfere with the lowest rotating antenna only two feel above. My best
> friend insists that it can be installed upside-down without any negative
> consequences, while still giving us the height we desire. I say this is
> preposterous. 

Although the precise design may have some impact on the answer, in
general, once an antenna is several wavelengths above ground, rightside up
and upside down lose their meaning.  For example, I have modeled the half
square for VHF in either orientation without any effect upon the pattern
or feed impedance.  I have also modeled verticals with sloping gp radials,
again without change.

Well above ground, the gp, if any, is nothing more than a top hat or
modified top hat.  It horizontally polarized radiation is cancelled in the
symmetry, and its vertically polarized radiation, if radials slope, is
simply part of the overall radiation from the total antenna structure.
Hence, up and down make no significant difference to the antenna
radiation field.

If the antenna is a vertical dipole or collinear array, independent of any
need for a hat/gp, then orientation makes no difference at all.

These note are predicated on the assumption that the antenna will not
clear the tower top in either orientation and therefore that tower
proximity effects will be equal in either orientation.

Hope these notes are useful.

-73-

LB, W4RNL


L. B. Cebik, W4RNL         /\  /\     *   /  /    /    (Off)(423) 974-7215
1434 High Mesa Drive      /  \/  \/\     ----/\---     (Hm) (423) 938-6335
Knoxville, Tennessee     /\   \   \ \   /  / || /      (FAX)(423) 974-3509
37938-4443     USA      /  \   \   \ \       ||              cebik@utk.edu
         URL:  http://funnelweb.utcc.utk.edu/~cebik/radio.html




--
FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com
Search:                   http://www.contesting.com/km9p/search