Contact us: Gauteng: 012 657 0960 | Cape Town: 021 555 3207 | Durban: 031 564 7283 | Nelspruit: 013 752 4654
Free Space Loss
Loss of power over distance (assuming no FRESNEL Effect and nothing in the way). This a very idealised calculation and in practice everything interferes with the signal but it will give you a reasonable approximation of the actual loss over distance.

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.

Frequency Distance   Result
 MHz  Km
OR
 Miles
 dB

  1. Free space loss = 36.56 + 20Log10 (Frequency) + 20Log10 (Distance in miles)

  2. Calculator normalises all distances to miles

  3. Miles to Kilometers = 1.609

  4. Kilometers to miles = 0.621

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 effective earth curvature at the mid-point of the Total link distance using the effective earth radius.

Total Link Obstacle Distance 1st Fresnel Zone Radius
 Km
OR

 Miles
 Km
OR
 Miles
 m
at
 Km
 ft
at
 Miles
Frequency   60% No Obstacle Radius
 MHz    m  ft
  Earth Height (mid-point)
     m  ft
  1. Calculator normalises all distances to kilometers and meters

  2. Miles to Kilometers = 1.609

  3. Kilometers to miles = 0.621

  4. feet to meters = .3048

  5. meters to feet = 3.28

  6. 1st Fresnel Zone radius (Km) = 17.3 x Sqr root ((Obstacle Distance x (Total Link - Obstacle Distance)) / (Frequency in GHz x Total Link))

  7. 1st Fresnel Zone radius (miles) = 72.6 x Sqr root ((Obstacle Distance x (Total Link - Obstacle Distance)) / (Frequency in GHz x Total Link))

  8. Obstacle free radius = 0.6 x 1st Fresnel Zone radius

  9. Radius of nth Fresnel zone (meter) = sqr root ( (n x wave length x Obstacle distance x (Total Link - Obstacle Distance)) / Total Link )

  10. wave length (meters) = speed of light (299,792,458 m/s) / frequency in Hz

  11. Earth curvature calculation = (Total Link) 2 /(8 * effective earth radius)

  12. effective earth radius = 4/3 * Earth radius

  13. Earth radius = 3963 miles, 6378 Km

Power in milliWatts to dBm (and vice versa) . Enter the 'Transmit Power' (A or G above) in milliWatts OR the 'Power Ratio' in dBm and click the appropriate 'Calculate' button. 1 Watt = 1000 milliWatts.

Calculations and equations used.

Transmit Power   Result
mW  dBm
Power Ratio   Result
 dBm  mW
  1. mW to dBm = 10Log10(Watts) + 30

  2. dBm to mW = 10(dBm/10)

This calculator allows you to calculate the voltage drop and required power supply for homebrew Power over Ethernet hardware. What's Power over Ethernet? Check out this page.

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!

Device Information:
Cable Information:
Input Voltage:
(Volts)
Input Current:
(Amps)
Wire Gauge:
(AWG #)
Power Pairs:
(pairs used for power)
Cable Length:
(Feet)
Results:
Voltage Drop:
(Volts)
Required Supply:
(Volts)
Effective Gauge:
(AWG #)
Cable Resistance:
(Ohms)
Power Dissipation:
(Watts per Foot)