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[antennaware] Homebrew vertical construction

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Subject: [antennaware] Homebrew vertical construction
From: (Gary Breed)
Date: Wed, 23 Sep 1998 09:20:23 -0400
Good to hear from you,. L.B.,

A few follow-up comments...

a.  In free space, where there are no reflections, the hat vertical has a
larger length of high current than the 1/4 wl w/gp.  Hence, for straight
out (tangential) radiation, we would expect higher gain relative to the
standard (dBi) than from the 1/4 wl w/gp.

b.  Over ground, the hatted vertical has some interesting properties
relative to the way in which you set up the project.  Since the antenna
feedpoints--1/4 wl down from the top--are the same, we should look at the
radiation originating below that point.  

The most notable thing about the "bottom hat" is how rapidly it falls off
in maximum gain, whether adding a small hat at the vertical dipole
end of the experiment, or shortening the 1/4 wave radials at the other
end.  It's gain is always below a straight line between the START and
END points.

c.  The sloped radial (type 1) antenna is quite interesting

I also considered that the sloped radials slightly skewed the main
lobe upwards, improving the summation with the reflected wave.

d.  If you were working with higher altitudes for the antennas, 
This would be important if someone
replicates this experiment for 40 meters, for example.

You're right -- a brief look at this scenario will convince anyone 
with that kind of available height to use a horizontal antenna.

e.  The maximum gain differential, although appearing very distinct, is
still about 1/2 dB or less than 0.1 S-unit

True, although the best-to-worst ratio is 1 dB, which might be
statistically significant in, say, a contest situation. This difference would 
also be multiplied in an array, such as a four-square.

f.  Average ground is in fact one of the lowest gain grounds over which a
vertical antenna system can be placed. 

Look at Georgia on your conductivity map!  "Average" ground is
better than I have under my antennas!

g.  I concur that more radials in the models are useful to try, although
since you are using a wholly elevated system, You might make the increases
modest for each replication.

An increase from four to eight is probably sufficient to establish
a trend.

I hope something in these notes will be useful to you.


73, Gary K9AY

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