Ensuring line-of-sight (LOS) clearance between transmitter and receiver antennas is crucial for establishing a reliable microwave link in mobile communication. Here’s how you can ensure LOS clearance effectively:
Figure 1
1. Conduct a Site Survey
Before installing antennas, conduct a comprehensive site survey to assess potential obstructions along the path:
Use Topographic Maps: Obtain topographic maps or digital elevation models (DEM) to visualize the terrain between transmitter and receiver locations.
Survey Tools: Use survey tools such as GPS devices and laser rangefinders to accurately determine the locations and heights of potential obstructions.
2. Identify Potential Obstructions
Natural Obstructions: Identify natural obstacles like hills, mountains, trees, and vegetation that could obstruct the LOS path.
Man-Made Structures: Consider buildings, towers, power lines, and other infrastructure that may interfere with the LOS.
3. Perform Path Analysis
LOS Analysis Software: Use specialized software tools (e.g., Pathloss, Radio Mobile, Microwave Link Calculator) to simulate the propagation path and analyze LOS clearance.
Digital Terrain Models (DTM): Overlay digital terrain models onto path profiles to visualize potential obstructions and verify LOS.
4. Calculate Fresnel Zone Clearance
Fresnel Zone: The Fresnel zone is an elliptical-shaped area surrounding the direct LOS path. Clearing this zone of obstructions is critical to minimize signal degradation due to diffraction.
Fresnel Zone Clearance Calculation: Calculate the radius of the Fresnel zone at various points along the path and ensure obstructions do not encroach upon it. Typically, at least 60% clearance of the first Fresnel zone radius is recommended for reliable performance.
5. Antenna Height and Elevation
Antenna Elevation: Install antennas at sufficient height to establish a clear LOS path over any intervening obstacles.
Antenna Mounting: Use mounting hardware that allows precise adjustment of antenna azimuth (horizontal direction) and elevation (vertical angle) to achieve optimal alignment.
You can perform all the above steps using your cellphone with an app called Microwave Link Calculator. With just a few simple steps, you can achieve the results shown in Figure 1.
Step 1: Input the required parameters for the link, such as antenna height, frequencies, transmit powers, antenna diameter, antenna gain (typically 0.7), and GPS coordinates. You can manually input GPS coordinates for each site or tap the northwest arrow icon (if you are on site) or tap the map icon to select on the map.
Step 1
Step 2: After tapping the Calculate button, you will receive the basic terrain elevation profile and essential Microwave Link output parameters, such as azimuths...
Step 2
Step 3: Identify natural obstructions or man-made structures by tapping the building icon on the map.
Step 2
Step 4: Once identified, you will see the elevation profile with the obstacles. Depending on the situation, you can adjust input parameters, such as antenna height, to ensure Line-Of-Sight (LOS) clearance by tapping the pencil icon.
Step 4
Step 5: Obtain the optimal results, and utilize the output parameters for LOS clearance in the microwave link: azimuths, Rx Powers, installed antenna height.
Step 5
During the installation process, if you are at one of the two sites, there is no need to use a traditional compass. You can refer to the map on your phone to approximate the target for tuning the azimuth, or use the built-in compass by tapping the AZ icon on the map. Ensure you are positioned at the tower for accurate GPS parameters. The application will notify you with a vibration signal when the correct azimuth is detected.
The Microwave Link Calculator app is available for both iOS and Android devices.
For iOS devices:
For Android devices:
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