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[aprssig] PHG and HAAT

Robert Bruninga bruninga at usna.edu
Fri Oct 14 19:30:36 UTC 2005


>>> schiers at netins.net 10/14/05 12:07 PM >>>
>Could you elaborate more on why Radio Mobile's 
>HAAT is inappropriate for the HAAT value in PHG?

I could be wrong, (havent used the program)
but if the HAAT it is calculating is the standard
"HAAT" as defined by the FCC (10 points going out
10 miles along 4 radials), then that is what the 
FCC wants, and is completely consistent with the 
FCC's requirement.

But it can be of little value unless applied with a dose
of common sense.  A typical mountain is not in the
middle of a city.  Hence repeaters and digipeters
are often on hillsides or mountains to the side of 
a coverage area and the effective height of the
antenna in one direction might be 1100 feet above
the general area of interest.  Yet it could be only
100 feet or less off the backside if the mountain has 
other ones behind it.

Thus, that computer program which is designed to
give the FCC only a single number called "HAAT"
yields the average.  IE, 500'.   But the real answer
is 100' off the backside towards the other mountains
and 1100' in the direction of the intended users.

APRS attempts to mitigate this problem by allowing
one to enter a PHG of 500 feet  but then also entering 
a favored direction which offsets the circle by 6 dB 
or so in the favored direction (double the range) and 
reduces the range in the back direction (halves the 
range).  

In effect, this does a pretty good job of conveying to
the viewer of this display, the favored direction and
a realistic coverage in that direction.

Having spoken may way through that, you will notice
that because the circle is offset, then it does more
or less accomodate the original "average" HAAT
by making the 500 average appear to be 1000 in the
given direction.  So in that sense, using the program's
HAAT will work just fine in this case, but only after
adding the dose of common sense.

Bob Wb4APR



----- Original Message ----- 
From: "Robert Bruninga" <bruninga at usna.edu>
To: <aprssig at lists.tapr.org>
Sent: Friday, October 14, 2005 10:57 AM
Subject: Re: [aprssig] PHG and HAAT



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