Defines how much clearance you need (yes you need more than simple Line-of-Sight) and for longer links > 3 Km (2 miles) whether you may have a ground clearance problem from our friendly planet. M. Fresnel and his theories.
Enter the Total link distance (in Miles or Kilometers), if you do not enter an Obstacle distance (in Miles or Kilometers) the calculator will use the mid-point for all calculations (Note: assumes antennas at same height). Finally enter the system Frequency in MHz and then click the 'Calculate' button. 1 GHz = 1000 MHz e.g. 2400 = 2.4 GHz.
The calculator will generate the radius of the 1st Fresnel zone only (at the obstable point or the mid-point), the 60% (no obstacle) radius and the height of the earth curvature at the mid-point of the Total link distance using the effective earth radius.
Calculations and equations used.
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Calculator normalises all distances to kilometers and meters
Miles to Kilometers = 1.609
Kilometers to miles = 0.621
feet to meters = .3048
meters to feet = 3.28
1st Fresnel Zone radius (Km) = 17.3 x Sqr root ((Obstacle Distance x (Total Link - Obstacle Distance)) / (Frequency in GHz x Total Link))
1st Fresnel Zone radius (miles) = 72.1 x Sqr root ((Obstacle Distance x (Total Link - Obstacle Distance)) / (Frequency in GHz x Total Link))
Obstacle free radius = 0.6 x 1st Fresnel Zone radius
Radius of nth Fresnel zone (meter) = sqr root ( (n x wave length x Obstacle distance x (Total Link - Obstacle Distance)) / Total Link )
wave length (meters) = speed of light (299,792,458 m/s) / frequency in Hz
Earth curvature calculation = (Total Link) 2 /(8 * effective earth radius)
effective earth radius = 4/3 * Earth radius
Earth radius = 3963 miles, 6378 Km
