In the United States in the 220 MHz band some of the regulations have requirements that are dependent on Height Above Average Terrain (HAAT). The FCC define this in CFR Title 47, Volume 4, Part 73 in sections 310 and 313. These definitions are based on area coverage and consider the area around the transmitting antenna, which may not be applicable for PTP use with directional antennas.
In PTP mode LINKPlanner calculates a worst case value, based on the antenna height at an end above the minimum ground level along the relevant section of the path towards the other end and displays a warning if this value exceeds the regulation. When the warning is displayed the user is advised to calculate the actual value (using the FCC’s Antenna HAAT Calculator) and consult the regulations.
To calculate the actual HAAT, start with the following information:
Put LINKPlanner’s Units in the format that the FCC’s Antenna HAAT Calculator is expecting. Select Tools, Options, Units, see Options (Preferences).
- Change the Latitude/Longitude to deg:min:sec (ddd:mm:ss.ssP).
- Change the Height to Meters.
Open a web browser and use the FCC’s Antenna Height Above Average Terrain (HAAT) Calculator (https://www.fcc.gov/media/radio/haat-calculator) to calculate the actual HAAT.
Site’s latitude and longitude
- Go to the Network Sites list in LINKPlanner to find the site’s latitude and longitude, see Displaying the Sites List.
- Enter the site’s latitude and longitude, and select the NAD83/WGS84 (worldwide) radio button.
Antenna height AMSL (in meters)
At the link end with the yellow warning icon (Right site or left site: Note that the HAAT may be different at each link end), note the Antenna Height in meters, this is the Antenna Height Above Ground Level (AGL).
To see the terrain heights double-click on the Profile visualization chart and the Profile Editor page is displayed.
- The left site’s Terrain height Above Mean Sea Level (AMSL) in meters is at the top of the Profile Editor.
- The right site’s Terrain height AMSL in meters is at the bottom of the Profile Editor.
The Antenna height AMSL (in meters) is the Antenna Height (AGL, meters) plus the Terrain height (AMSL, meters).
Enter the Antenna height AMSL (in meters) in the “height (in meters) of the antenna radiation center above mean sea level (RCAMSL)” box.
For multiple ends the Antenna Height (AGL) and Terrain Height (Ground Height) are also in the PTP Links List, see Displaying PTP Links, adjust the table using Managing List Views. Set the following columns to display Left (Right) Height (m) and Left (Right) Ground Height (m).
Under “Enter number of evenly spaced radials (8 minimum, 360 maximum):”, select “8 (every 45°)”.
Under “Terrain database:”, select “FCC terrain data (continental US only)”.
Left-click on the “Send Data” button to obtain the actual HAAT.
Title 47, paragraph 90.259(4) states that the HAAT may not exceed 152 meters (500 foot).
CORRECTIVE ACTION
If the actual HAAT is greater than 152 meters, reduce the antenna height (and re-run the FCC HAAT Calculator by hitting the back-arrow button and entering only the new Antenna height AMSL) until the actual HAAT is 152 meters or less.
Title 47, paragraph 90.729(a) contains the following table for ERP vs. Antenna Height. If the actual HAAT is above 450 meters (or a much higher gain antenna is used) then the ERP may need to be reduced.
| Antenna height above average terrain (HAAT), metres | Effective radiated power (Watts) |
|---|---|
| Up to 150 | 500 |
| 150 - 225 | 250 |
| 225 - 300 | 125 |
| 300 - 450 | 60 |
| 450 - 600 | 30 |
| 600 - 750 | 20 |
| 750 - 900 | 15 |
| 900 - 1050 | 10 |
| Above 1050 | 5 |
The EIRP in dBm is displayed on a PTP link in the “Configuration at Each End” section.
CORRECTIVE ACTION
If the combination of actual HAAT and ERP exceed the limits from the table, either reduce the antenna height (and re-run the FCC HAAT Calculator by hitting the back-arrow button and entering only the new Antenna height AMSL) or reduce the ERP, until the requirements in the table are met.
To reduce the ERP, either in the Configuration at Each End section tick the User Limit option and enter the required EIRP or change the antenna size.