Posted by
Darwin, Keith on
Mar 05, 2007; 7:06pm
URL: http://elecraft.85.s1.nabble.com/Re-Vertical-antennas-tp444447p444449.html
Good info Steve,
I wonder a couple of things though. First, why 8 degrees for the
takeoff angle? That puts it low enough that you're into the ground
effect suck-out zone fairly heavily. I'd have though something like 25
degrees would be a more representative angle for typical communications
use.
Also, what is the effect on the Force 12 antenna if it is between 1 foot
and 28 feet off the ground? What if it is 15 feet off the ground (i.e.
on my garage roof)?
- Keith N1AS -
- K2 5411.ssb.100 -
-----Original Message-----
From: Stephen W. Kercel
The discussion of verticals has inspired me to do a bit of EZNEC
modeling. I plotted the azimuthal pattern at an 8 degree takeoff angle
for several different 80 meter configurations. In all 3 cases, I've
assumed average ground.
The first case is the classical full size vertical, with a quarter wave
monopole element and 128 quarter wave radials. *snip* the pattern is an
omni pattern with a signal strength at 8 degrees takeoff angle of -2.72
dBi.
The second case is the Force 12 vertical dipole, with no radials. ...
bottom of the antenna elevated 28 feet above the ground. ... The signal
at 8 degrees takeoff angle is an omni pattern at -3.09 dBi. ... an
undetectable quarter dB worse than the ideal full size quarter wave
configuration.
How important is the mounting height? It matters. For the same
configuration except with the bottom 1 foot above the ground, the signal
strength at 8 degrees takeoff angle is -5.8 dBi. This is a quite
noticeable >3db degradation from the full featured quarter wave
configuration.
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