[TowerTalk] 15 meter yagi height for 6000 miles

[Frank]

David Gilbert wrote:

>That says more about what some people read into computer programs than 
>it does about about "what some computer says is optimum".  VOACAP is 
>based upon empirical data and statistical analysis, and as such it 
>displays predicted (not absolute) results for a representative (not 
>absolute) time period within certain accuracy limits .  HFTA used VOACAP 
>to determine the predicted best takeoff angles for various paths **as an 
>average over an entire eleven year sunspot cycle**.
>
>As a planning tool HFTA is the best we have to work with.  It is based 
>upon sound science and was written by a competent software engineer.   
>It does pretty much exactly what it was intended to do ... give you the 
>best chance of optimizing your results over a long period of time.  
>Anybody who thinks that it will hold true in every instance, or that 
>actual results won't often be even better than predicted, doesn't 
>understand the tool that they are using or the physics behind it.
>  
>
This is the best argument I have yet heard on why the best available may 
not be good enough.

If it requires an exceptional understanding of the physics behind it to 
understand why it is not providing useful results, then it is pretty 
much worthless as a tool for those seeking practical realtime applications.

Most hams are more interested in practical antenna designs and not so 
much in the physics that explains why a certain computer model can't 
seem to provide useful answers.

Figures don't lie but it is very simple to come to false conclusions 
using statistics and averages.  Statistical averages over time can be 
paticularly misleading.

In my opinion you can get better results in less time by simply reading 
a good book on antenna design.