[TowerTalk] Dipole gain?

[Jim Brown]

On Tue,12/9/2014 1:46 PM, Ken wrote:
> In actuality, “gain” in a non rotatable antenna is a myth.

False. Gain for antennas is usually expressed as dBi, meaning dB 
referenced to an ideal isotropic radiator. Gain is not a single number 
(unless the antenna is isotropic) -- it varies with both vertical and 
horizontal angle.

An ideal (lossless) dipole in free space has a PEAK gain (that is, 
broadside to it) of 2.18 dBi. Mount that dipole horizontally over real 
ground and the earth provides a reflection in the far field that creates 
a vertical pattern. Assuming no earth losses, the Peak gain will now be 
3-6 dB greater at the vertical angle where the direct wave from the 
antenna combines precisely in phase with the wave reflected by the earth.

The shape of the vertical pattern will be entirely dependent upon the 
height of the horizontal dipole as a fraction of a wavelength, but will 
be almost independent of soil conditions.

Mount that same dipole VERTICALLY and it will interact very differently 
with the earth, and will be VERY dependent on the quality of the soil.  
There are some tutorials about all of this on my website. 
k9yc.com/publish.htm

http://k9yc.com/VerticalHeight.pdf

http://k9yc.com/VertOrHorizontal-Slides.pdf

73, Jim K9YC