I am changing the subject slightly hoping to avaid the flaming that
has started.

I will briefly sumamrize some things I learned from my experiences
with 4NEC2. Maybe this will inspire. Remember I am a beginner.

First of all I modeled my rhombic antenna I was building. I used an
inputting method called geometry edit. This is fairly easy way to
input the dimensions of the wires of the antenna and gave valid
output. But I found it cumbersome to change the dimensions. In fact
I had to do some trig to figure out the X,Y coordinates of the changed
antenna. But it DID work, and I found out a lot about modeling and
the rhombic, but I could not get the "optimizing" feature to work. It
kept telling me I had no variables to change. So I did some reading
in the generic NEC2 documentation and learned about "cards." And then
I studied some examples and learned how to input data with the NEC
editor. With this method, you define variables such as the angle
between the legs of the rhombic, and you only need to do it once.
Then you can have the program change the variable for you and output
the data. For example you could include a variable for the
terminating resistor, have the program change the value of it while
checking for forward gain. Or you could change the lengths of the
wires easily or the angle, or make one wire longer than another,
anything you want. Also can do a frequency sweep to see where your
antenna is resonant.

So I will close with two things I have discovered through my
experimenting with the program and with getting out in the woods and
putting up wires. The first is that I believe the model accurately
determined the characteristics of my rhombic. It showed I could
expect about 13 dbi gain, about 22 db f/b and a 20 degree beamwidth,
at a height of about 30 ft. It also showed about 12 dbi gain for a 3
element yagi at about 40 ft. When I built the rhombic and compared it
to my 3 ele yagi I found the performance on extremely weak signals
near the noise level were essentially the same on both antennas, and
the f/b on the rhombic was phenominal. Just what the model predicted.
In building the antenna the model told me it didn't make much
difference if the wires were 25 feet shorter than I had started with,
so it was more convenient to build and attach to trees I had. So I
believe the model so far. The second thing I have learned, (and I am
building a small collection of my experimental antenna files) is
trying to find the best way of getting some gain on 40 meters into
Europe from NJ. I started with my inverted vee at 40 ft. I then
added a reflector (supported from a guy wire). Then tried converting
the inv vee to a delta loop. Wow that was a disappointment. I guess if
you have radiation from only 40 feet up it is not a good idea to
distribute that current into elements at a lower angle !!! Then my
buddy Yuri, K3BU, told me feed it 1/4 wavelength down from the peak
and that would get my angle down and get me some vertical radiation.
Easy to do with the program, and Yuri was right.

Oh I tell you this is fun stuff. Much more fun than flaming each
other on newsgroups. My suggestion - do a google search, find some
software, bang it around on your keyboard, write to me, trade some
antenna files, maybe even pull up some wirees into trees.

Oh incidentally, I forgot to mention. Get this. The last thing I
learned was how to attach feedlines (the program calls it a
transmission line, or a TL card) to two antennas. Make the lines long
enough to give you a lot of slack. Then you can move your two active
antennas all around and see what kind of pattern you get. Put them
end to end, change the spacing. Put them in front of one another,
like a JK beam and change the spacing or the lengths. Cool stuff,
really cool stuff.

Rick K2XT

There is NEC List for discussion of computational electromagnetics
http://www.robomod.net/mailman/listinfo/nec-list

Yuri, K3BU


"Rick" wrote in message
...
I am changing the subject slightly hoping to avaid the flaming that
has started.

I will briefly sumamrize some things I learned from my experiences
with 4NEC2. Maybe this will inspire. Remember I am a beginner.

First of all I modeled my rhombic antenna I was building. I used an
inputting method called geometry edit. This is fairly easy way to
input the dimensions of the wires of the antenna and gave valid
output. But I found it cumbersome to change the dimensions. In fact
I had to do some trig to figure out the X,Y coordinates of the changed
antenna. But it DID work, and I found out a lot about modeling and
the rhombic, but I could not get the "optimizing" feature to work. It
kept telling me I had no variables to change. So I did some reading
in the generic NEC2 documentation and learned about "cards." And then
I studied some examples and learned how to input data with the NEC
editor. With this method, you define variables such as the angle
between the legs of the rhombic, and you only need to do it once.
Then you can have the program change the variable for you and output
the data. For example you could include a variable for the
terminating resistor, have the program change the value of it while
checking for forward gain. Or you could change the lengths of the
wires easily or the angle, or make one wire longer than another,
anything you want. Also can do a frequency sweep to see where your
antenna is resonant.

So I will close with two things I have discovered through my
experimenting with the program and with getting out in the woods and
putting up wires. The first is that I believe the model accurately
determined the characteristics of my rhombic. It showed I could
expect about 13 dbi gain, about 22 db f/b and a 20 degree beamwidth,
at a height of about 30 ft. It also showed about 12 dbi gain for a 3
element yagi at about 40 ft. When I built the rhombic and compared it
to my 3 ele yagi I found the performance on extremely weak signals
near the noise level were essentially the same on both antennas, and
the f/b on the rhombic was phenominal. Just what the model predicted.
In building the antenna the model told me it didn't make much
difference if the wires were 25 feet shorter than I had started with,
so it was more convenient to build and attach to trees I had. So I
believe the model so far. The second thing I have learned, (and I am
building a small collection of my experimental antenna files) is
trying to find the best way of getting some gain on 40 meters into
Europe from NJ. I started with my inverted vee at 40 ft. I then
added a reflector (supported from a guy wire). Then tried converting
the inv vee to a delta loop. Wow that was a disappointment. I guess if
you have radiation from only 40 feet up it is not a good idea to
distribute that current into elements at a lower angle !!! Then my
buddy Yuri, K3BU, told me feed it 1/4 wavelength down from the peak
and that would get my angle down and get me some vertical radiation.
Easy to do with the program, and Yuri was right.

Oh I tell you this is fun stuff. Much more fun than flaming each
other on newsgroups. My suggestion - do a google search, find some
software, bang it around on your keyboard, write to me, trade some
antenna files, maybe even pull up some wirees into trees.

Oh incidentally, I forgot to mention. Get this. The last thing I
learned was how to attach feedlines (the program calls it a
transmission line, or a TL card) to two antennas. Make the lines long
enough to give you a lot of slack. Then you can move your two active
antennas all around and see what kind of pattern you get. Put them
end to end, change the spacing. Put them in front of one another,
like a JK beam and change the spacing or the lengths. Cool stuff,
really cool stuff.

Rick K2XT

"Yuri Blanarovich" wrote in news:eme7vr$fk7$1
@aioe.org:

There is NEC List for discussion of computational electromagnetics
http://www.robomod.net/mailman/listinfo/nec-list

Yuri, K3BU



But I would think that such discussions are welcome here too!


- 73 de Mike KB3EIA -

But I would think that such discussions are welcome here too!

Yes I am sure they are. From time to time Yuri and I try to get things
going here, to get participants' minds back onto antennas. It's a tough
road.
So instead, Yuri and slop around in the mud fixing up old antennas and
towers and
having our antenna discussions in person.

Rick K2XT