[aprssig] FCC's Calculation of HAAT

Eric H. Christensen kf4otn at earthlink.net
Wed Dec 15 18:26:48 EST 2004

§ 24.53 Calculation of height above average terrain (HAAT).
(a) HAAT is determined by subtracting average terrain elevation from
antenna height above mean sea level.
(b) Average terrain elevation shall be calculated using elevation
data from a 30 arc second or better Digital Elevation
Models (DEMs). DEM data is available from United States Geological
Survey (USGS). The data file shall be identified. If 30 arc second
data is used, the elevation data must be processed for intermediate
points using interpolation techniques; otherwise, the nearest point
may be used. If DEM data is not available, elevation data from the
Defense Mapping Agency’s Digital Chart of the World (DCW) may be
(c) Radial average terrain elevation is calculated as the average of
the elevation along a straight line path from
3 to 16 kilometers extending radially from the antenna site. At least
50 evenly spaced data points for each radial
shall be used in the computation.
(d) Average terrain elevation is the average of the eight radial
average terrain elevations (for the eight cardinal
(e) The position location of the antenna site shall be determined to
an accuracy of no less than ±5 meters in both the horizontal
(latitude and longitude) and vertical (ground elevation) dimensions
with respect to the National Geodetic Reference System.

kf4otn at amsat.org

Project OSCAR Member
AMSAT-NA Member: 35360
AMSAT Eastern North Carolina Area Coordinator

-----Original Message-----
From: aprssig-bounces at lists.tapr.org
[mailto:aprssig-bounces at lists.tapr.org] On Behalf Of Chris Rose
Sent: Wednesday, December 15, 2004 17:56
To: TAPR APRS Mailing List
Subject: Re: [aprssig] bad PHG, or lots of big towers?

I would still ask exactly what is average terrain?  

Is it the spot of ground the tower sits on or is it
something else?

If a small mountain say 5k high sits in the middle of
a plain somewhere, from where is the average terrain

The base of the tower or the flat land at the base of
the mountain?


--- Steve Dimse <k4hg at tapr.org> wrote:

> On 12/14/04 at 9:38 AM Gerry Creager n5jxs <gerry.creager at tamu.edu>

> sent:
> >Height Above Ground at the tower base.  So: What's
> the Height Above
> >Average Terrain?  That is, in my opinion, the
> height that should be
> >advertised.
> >
> Not just an opinion, the spec is very clear on the
> fact that the H in PHG is
> above average terrain...
> Steve K4HG

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