[aprssig] [APRS] Re: PHG and Height Above Average Terrain debate
bruninga at usna.edu
Sun Aug 28 13:05:17 CDT 2011
> Back to the HAAT topic ...
> I found this calculator :
it gives you ther HAAT for every radial around your QTH.
Like any "equation", the results depend entirely on what you want to do. Yes, there is a very formal process for calculating the HAAT EXACTLY, but such an exact number might be practically meaningless in many applications.
For example. The HAAT is an AVERAGE. For a tall antenna in a relatively homogeneous topology, such a calculation will give about what you want. An average in all directions.
HOWEVER, it is practically meaningless:
1) If the *majority* of users are all in one general direction
2) or 2, the *majority* of Hills or plains are in one general direction.
Generally, most REPEATERS and DIGIPEATERS are on hills that serve hams, generallly located to serve and area where all the people are. And people are generraly located not on mountaint tops but in valleys or on plains adjacent to hills.
So I always say to figure the HAAT in the general direction of where most of the users are, and or in the direction of the Plains where it will be the greatest and the offset the pattern in that direction. This requires *human* judgment. Just like *every* equation on earth depends on the conditions under which it should and should not be applied.
COmputers and equations give perfect answers. usually wrong if the conditions or the inputs are not properly accounted for.
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