User's Manual

19
4.2.5 Worked Example 1
2000m
Fresnel Zone
Line of Sight Obstruction Fresnel Zone penetration
Line of Sight
Figure 10 Worked Example
This example of figure 10 shows a case where a tree obscures the Line of Sight and the Fresnel
Zone has a building intrusion.
In this example:
• Free Space Path Loss = 114 dB
• Excess Path Loss for Line of Sight Obstruction = 20 dB
• Excess Path Loss for Fresnel Zone penetration = 10 dB
• Total Excess Path Loss = 30 dB
• Required Fade Margin from above look up chart = 11 dB
Calculation:
114 dB + 30 dB + 11 dB = 155 dB
The result of this calculation shows that this scenario would work with margin using the allowed
US power level (164 dB max path loss). The normal operational mode will be 16QAM but there
will be occasional drops to BPSK mode.
4.2.6 Worked Example 2
This example in figure 11 shows a case where the Line of Sight is obstructed by a terrain obstacle.
In this example:
• Free Space Path Loss = 120 dB
• Excess Path Loss for Line of Sight Obstruction = 20 dB
• Required Fade Margin from above look up chart = 8 dB