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Height is of no matter to free space models. I don't know of any ideal height for a 5/8 wave, unless I had a perfect model and could raise it and check to see if the magnitude of current flows on the attached mast made a difference in the gain and pattern and even then it would be a stretch to determine because height itself affects the gain and angle. This business of determining cause and effect is a very illusive subject.

 

Right now, I suspect that models with more current on the mast may show more gain as a result, and this current difference may be due, more or less, to different heights, but I was surprised to see your most recent idea, 274" x 107" without a top hat, show far less current flow on the mast of the antenna model I started with, and that was without any change in height. So, I could be all wrong. There is far more to what goes on here than just trying to see a difference between .625/.64, and that is why I'm trying to check things out.

 

If you will compare the model "NB idea no top hat 011612" that I just posted for you, to the first model "I-10K w matcher 18' mast #2" you will note, checking out the red line currents on these two masts, that the magnitudes are different, and so is the gain and angle. Which looks best to you?

 

It is my opinion that this magnitude of currents on the mast is significant to the gain, angle, and pattern shown. So, we can't always just go by the max gain and/or angle a model might show us, the currents indicated are important also. This might also account for some of why Bob85 tells us about modeling antennas without including the mast and feed line is problematic.

 

I guess I'm safe in claiming this much, changes in height are more significant that most realize. Increasing height is not just improving the range of your antenna. At some heights the match might be right on, and at other heights things might go to hell in a hand basket.

 

Maybe this is why we hear so many complaints from guys installing antennas like the Imax/A99 and maybe others, that should be about as close to match set as you're likely to get working CB. So, maybe all this complaining about the poor workmanship is not always the answer. Could it also have to do with the worst case scenario for the installed height?