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[aprssig] Re: Calculating HAAT(was lots of big towers?etc)

Robert Bruninga bruninga at usna.edu
Tue Dec 14 20:26:45 UTC 2004


>>> jfkraus3 at cox.net 12/14/04 3:12:42 PM >>>
>>On a topographic map, plot concentric circles centered on your tower

>>location.  
>
>How far out are the circles? 1ft 1mi 100mi?  It will affect the
calculation. 

The official HAAT required by the FCC on formal submissions
is out to 10 miles, but again, if the digi is so high that
it can see out to 80 miles, then it is the ground out about 50 miles
that will have the greatest impact on actual range, and
not the initial 10 miles which might still be on the same
mountain.

So common sense should really be the factor based on
what the area is.  Taking average levels out 100 miles
would not make sense since the signal wont get that
far, and taking them at 5 miles for a digi that is at 10,000
feet wont make much sense either.  Unless of
course you put it in the middle of a FLAT top mountain
that is 10 miles across then the average terrrain that 
will block the signal before it gets to the valley IS
only 5 miles...  

Again, common sense must be applied.

The FCC equation is good for getting "consistent"
results for their data base, but getting a value that
matches your real-world situation is a horse of
a different color.

Also, if the area towards 90% of your users is
east, and no one lives to the west, then use the
average terrain in the direction of most use...

etc...

Bob.
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