[aprssig] bad PHG, or lots of big towers?

Jason Winningham jdw at eng.uah.edu
Tue Dec 14 11:38:48 EST 2004

> English is not my fisrt languaje.

Quite alright; some of us who have English as a first language don't do 
all that well sometimes. (:

> Can you please tell me what HAAT means? If HAAT need some 
> calculations, can you please explain it to me?

HAAT is Height Above Average Terrain, and there is a specific formula 
that goes like this:

On a topographic map, plot concentric circles centered on your tower 
location.  Draw lines radiating outward from your tower location at 0, 
45, 90, 135, 180, 225, 270, and 315 degrees (every 45 degrees starting 
at 0).  Everywhere a circle and radial line intersect, add the 
elevation of that point (total of 40 points).  Divide this total by 40; 
this is the average ground level.

Add your elevation at the tower location plus the antenna height above 
the ground and subtract the average ground level calculated previously. 
  The result is HAAT.

Note for metric users: HAAT for APRS is in feet.

http://www.oarc.com/102.pdf has a worksheet to help you calculate it 
manually, and another poster mentioned Radio Mobile, which is software 
that will do it for you.


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