[TowerTalk] Symptoms of antenna interaction?

[Jim Brown]

On 3/23/2021 12:30 PM, Al Kozakiewicz wrote:
> Is this symptomatic of interaction, i.e. feed point characteristics change while resonance frequency remains the same?

If you can do modeling, try modeling dipoles for the bands where you are 
concerned about interaction, with a generator in only one of them. Open 
the View Antenna window. Then compute the far field response, and on the 
View Antenna window, go to View, then Objects, and check the box for 
Currents. You can check other boxes if you want to see those things. I 
like to show Axes and Segments to help me tweak the model. Then in the 
View Antenna window, move the Zoom Current slider to make the currents 
large enough to see current distribution in the dipole with the 
generator, and look for current in the one without the generator. If 
there's no current, there's likely to be little interaction.

Repeat this process as you vary the length of the antenna you're not 
feeding, then move the generator to the other antenna and repeat the 
process.

This is not as accurate as full models, which are FAR more complicated, 
but it will tell you whether to look further. A dipole in NEC is simply 
a wire with a generator in the middle of it. Always use an odd number of 
segments for a dipole so that the generator can go in the center. Wires 
are entered by their x, y, and z coordinates.

73, Jim K9YC