Height Above Average Terrain (HAAT) is commonly used in the prediction of coverage by broadcast and land mobile system designers. HAAT provides a metric of the height of the transmitting antenna in relationship to its surroundings.
For coverage analysis, HAAT is more meaningful than tower height: an antenna mounted on top of a single story building on top of Pike’s Peak will have more coverage than a 500 foot tower in a river valley.
Calculating the HAAT for a given system requires the following data:
- lat/long coordinates of the transmit site
- Transmit site ground elevation (above mean sea level or MSL)
- Antenna height (above ground level or AGL)
- Average Height of a set of points in a 10 mile radius of the transmit site
Average Terrain Height is calculated by drawing a set of radii out from the tranmit site. On a topological map, one would draw lines out from the transmitter site at 0, 45, 90, 135, 180, 225, 270, and 315 degrees. The lines would extend out 10 miles, and would be marked every 2 miles. The elevation would be recorded for each radius every 2 miles.
The average terrain height would be calculated by adding all 40 points’ elevations together and dividing by 40.
These days… “There’s an app for that!”
Step 1: Determine lat/long coordinates for the transmit site (by GPS, online map, etc.) in degrees, minutes, and seconds
Step 2: Determine height of the center of radiation of the antenna in meters
Step 3: Determine ground elevation AMSL at transmit site (by GPS, online map, etc.) meters
Step 4: Calculate Radiation Center Above Mean Sea Level, RCAMSL, by adding transmit site AMSL and antenna center-of-radiation height.
Step 5: Choose one of the following:
FCC Web application
Radio mobile has an on-line version can provide HAAT. The tool provides all kinds of propagation and coverage analysis for VHF/UHF/Microwave systems. Radio Mobile can also be installed on a Windows computer. Free downloads of elevation data files local to your site are also required. The elevation data sets are large.
See the Off Site Tools page for more details of Radio Mobile.
Splat! Provides HAAT. Its a software package that run on Windows, Mac and Linux platforms. Free downloads of elevation data files local to your site are also required. The elevation data sets are large.
See the Off Site Tools page for more details of Splat!.