On 2/6/2011 6:14 PM, bpnjensen wrote:
[...]
Bruce:
I have EZNEC, which is a very good antenna modeling program. I
modeled your antenna for various frequencies and created a fairly
readable 3D plot of its pattern on various frequencies. In each
case, the horizontal wire points in the opposite direction from the
Y axis shown in the plots:
1 MHz:http://liberty.3950.net/Jensen%201.PNG
5 MHz:http://liberty.3950.net/Jensen%205.PNG
6 MHz:http://liberty.3950.net/Jensen%206.PNG
7 MHz:http://liberty.3950.net/Jensen%207.PNG
10 MHz:http://liberty.3950.net/Jensen%2010.PNG
15 MHz:http://liberty.3950.net/Jensen%2015.PNG
17 MHz:http://liberty.3950.net/Jensen%2017.PNG
22 MHz:http://liberty.3950.net/Jensen%2022.PNG
With all good wishes,
Kevin, WB4AIO.
--http://nationalvanguard.org/http://kevinalfredstrom.com/
Wow! These are amazing! Thanks, Kevin. I am somewhat surprised,
though, by the apparently omnidirectional character (at least
horizontally) on the lower freqs.
You're welcome.
Well, the omni pattern an octave or so around the quarter wave
resonance isn't too surprising, really, if you think about it.
The vertical section gives omnidirectionality in the horizontal
plane, but a null directly overhead. The horizontal part fills in
that null and is basically elliptical in the horizontal plane. So
they complement each other to produce an almost-omni pattern. Nice
antenna, really. My 150-foot inverted L was one of my favorite
antennas of all time for 75 meter ham use.
You might be able to enhance the low angles with a radial ground
system, but for receiving on the noisier low bands you might not be
able to perceive any improvement beyond higher S-meter readings. A
beverage antenna would give you low angle directivity, as would a
K9AY loop.
The higher end looks like a
mathematical nightmare!
That's the psychedelic butterfly pattern that Dave was talking about.
One thing notable too, is the lower angle of radiation on the higher
freqs. I wish I could attain those on the lower ones - but the only
way to do that is go higher, I guess.
If you want to suppress the high-angle part of the pattern (and make
nearby North American signals and static weaker compared to the
farther DX), going strictly vertical would help. A horizontal
antenna a half wave up has a similar effect (that's up about 100
feet for 60 meters).
Have fun,
Kevin, WB4AIO.
--
http://nationalvanguard.org/
http://kevinalfredstrom.com/