On Mon, 10 Sep 2007 08:51:56 -0500, "amdx" wrote:

I see that height above ground affects the gain and the angle of the
main lobe. (actually all lobes) The info I've seen shows best gain and lobe
formation somewhere between 1/4 and 1-1/2 wavelengths above ground.
So I have a 2.4Ghz yagi, does that mean I should put it 1/4 to 1-1/2
wavelengths
above ground? That means it would be 1-1/2" to 6" above ground.


Hi Mike,

All very true. However, the best gain aimed through your neighbor's
hubcaps isn't very useful.

Another point, at the frequency you are talking about, that "gain"
coming from the reflection from ground can be absolutely useless, or
worse, render a poor bit rate throughput (the appropriate topic thus
turns on the term "Fresnel Zone"). The principle mode of
communication is line-of-sight. In other words, you want both
antennas to be literally within "sight" of one another. For greater
range, you don't necessarily want more gain, you want more height.

More height gets you above the hubcaps and kneecaps of the world, and
out into blue sky where the sun, moon, and the stars are seen by
everyone. Very little power is required to transmit to the furthest
point on the terrestrial horizon. With an antenna mounted 100 feet
high, that is only 14 miles away and 100mW will give a clear signal
(at least at VHF). Adding more gain won't make that signal any
clearer, but you might want gain if the transmission power is in the
microwatts. Then you add elements.

Returning to the allusion to Fresnel Zones, this is where reflections
from the ground (which raises the "gain" you noticed) or nearby
buildings add out of phase and distort the bit shape of digital
transmissions. If your location is susceptible to such problems (and
forces a lot of retries in packets); then you want more "gain" in the
sense of actually achieving more selectivity. The antenna's added
elements react to these blurring reflections less, and focus on the
line-of-sight signal more.

73's
Richard Clark, KB7QHC