On Sat, 11 Oct 2014 18:04:07 -0000, wrote:

Jeff Liebermann wrote:

snip

Speaking of dipole antennas, I did this study a while back:
http://802.11junk.com/jeffl/antennas/vertical-dipole/index.html
Animated version:
http://802.11junk.com/jeffl/antennas/vertical-dipole/slides/animated-v-dipole.html
It's a 1/2 wave dipole at various heights above a real ground. Any
semblance to textbook dipole pattern is long gone.

Yep, ground has a huge effect on some types of antennas.

An instructive slide show would be the vertical pattern of a horizontal
1/2 dipole at .1, .2, ... .5 wavelengths over ground.

Another one would be a 3 element beam at those heights.

I can do both of these, but I'm busy/lazy this weekend. I also can't
find the program I used to create the annimated GIF file. Argh. It
would also be helpful if someone would specify the frequency range of
interest.

I also did a study of monopoles of various lengths above a ground.
There are a few that are less than 1/4 wave long which should help
with some short antenna phenomenon.
http://802.11junk.com/jeffl/antennas/Monopole/index.html
Length Gain
wl dBi
0.050 4.75
0.125 4.85
0.250 5.19
0.500 6.96
0.625 8.01
Notice that the gain doesn't really drop very much when the monopole
is shorter than 1/4 wavelength long. A 1/2 wave dipole exhibits a
similar lack of gain loss for short antennas. So, why are short
antennas generally frowned upon? Lots of reasons but the big one are
losses in the matching networks. the 0.050 wavelength antenna looks
like about 700 ohms impedance. The 0.125 antenna is about

Nope, the vertical does the same thing when shortened from 1/4 as a
dipole shortened from 1/2 wave.

Thanks, that's what I meant to say but never finished the posting. I
had to run and clicked "send" before I was finished scribbling the
last paragraph.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558