[TowerTalk] 15 meter yagi height for 6000 miles

[David Gilbert]

No ... HFTA does NOT require even a basic understanding of physics to be 
used and to be useful.   I never said anything about any need to have an 
"exceptional understanding" of anything to use the application.  You 
just made that up.  All it requires it that you read the damn manual ... 
the help file and the three or so pages in the ARRL Antenna Book that 
describe the application.  Everything I know about the program can be 
found there for the reading.

And OF COURSE statistical averages can be misleading ... particularly if 
you ignore the help information that tells you clearly that the program 
is based upon statistical averages and that you shouldn't expect the 
results to be rigorously applicable in specific instances.  That's 
pretty much the point I was trying to make in my reply to N4DB.   By 
definition there are always exceptions to an average.

I don't think you even understand what HFTA is supposed to do.  You can 
read all the antenna books you want and you won't get a very clear idea 
of what kind of elevation pattern your antennas have over your 
particular terrain.  HFTA has almost no relevance to antenna design per 
se and only uses combinations of standard antenna configurations 
(dipole, 2-element yagi, 3-element yagi, etc) to determine the effect of 
terrain on the pattern.

Dave   AB7E



On 3/2/2012 2:21 PM, Frank wrote:
> 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.
>