Enter the system Frequency in MHz and the distance in either Kilometers (Km) or Miles below and then click the 'Calculate' button. 1 GHz = 1000 MHz e.g. 2400 = 2.4 GHz.
Calculations and Equations used:
Free space loss = 36.56 + 20Log10 (Frequency) + 20Log10 (Distance in miles)
Calculator normalises all distances to miles
Miles to Kilometers = 1.609
Kilometers to miles = 0.621
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 effective earth curvature at the mid-point of the Total link distance using the effective earth radius.
Calculator normalises all distances to kilometers and meters
Miles to Kilometers = 1.609
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) = 72.6 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
mW to dBm = 10Log10(Watts) + 30
dBm to mW = 10(dBm/10)
Just enter your information in the five "Device Information" boxes and click
on "Compute". The input boxes have been initially filled in with generic information to save a
second or two for testing.
Important Note! The two most important inputs for power over anything are wire gauge and amps used. Wire gauge is easy to figure out
(it's either 22 or 24 for common Ethernet cable) but actual input amps is much trickier. You see, most devices list their maximum current
draw, not their "normal" draw. So if your access point says "6V at 1.5A" and is
100 feet away on 22 gauge wire, you would be tempted to use a 7.2V supply. But
the AP probably only really pulls in half an amp or less under normal
conditions, so you should be feeding it just 6.4V. You can fry your
equipment by putting too much voltage into it! So what to do? Simple, just
measure the normal current draw when the device is in use. Don't have the tools?
Well, then, just guess. Most devices that don't have a hard disk, Pentium 4, or
other power sucker actually draw very little current, making this whole
calculator less useful than you might think. Guess the actual draw by reducing
the listed amps by 50% to 75%. And hope for the best!