[TowerTalk] EZNEC question

[Jim Brown]

On 4/16/2013 6:21 PM, john nistico wrote:
> I am new to the program and having some trouble plotting a vertical yagi I want to build for 80 meters anyone care to help?

Look at their example antennas, choose a simple vertical, save it with a 
new file name, change the length to put it on 80M, study that and get 
comfortable with how it behaves, and look at the elements that define 
it. There will be a wire connected to ground, and there will be a source 
at the bottom end of it.  Tweak the length of the antenna so that the 
SWR bandwidth is centered where you want it, plot the vertical pattern 
and study it.

Once you've done all that, open the wire menu, and add a second vertical 
element that's about 5% taller than the first, placing it perhaps 0.2 
wavelength away.  Do NOT put a source in it.  Now plot the SWR and 
pattern of this new antenna, which is a simple 2-element vertical Yagi. 
Make some notes of the gain, and compute it at the center of your 
bandwidth, and again 100 kHz above and below.  Also look at the SWR curve.

Next, try changing the spacing between the two elements (leave the 
driven where it is, move the reflector perhaps 5-10 ft at  a time), and 
do the same plots you did before.  Also try shortening the reflector 2% 
or so. And so on. Spend all day doing this (or maybe two days) and by 
the time you've done that you will have learned how simple 2-element 
arrays work, and you'll be more comfortable with EZNEC.

You're lucky -- this is a nice, simple antenna to model, but you can 
learn a lot about both the antenna and NEC by this sort of process. I 
know -- I've done something quite similar with a 2-element horizontal 
Yagi for 80M.

73, Jim K9YC