Wireless Calculators
A Wireless System (more or less!)
Key: Green is good, Red is bad.
 Power Budget  total power of your system in dBm.
 Free Space Loss  power loss over distance.
 System Performance  How far will it go, will it get there or what is my Operating Margin?
 Fresnel Zones  How much more than LOS or how high should my antenna be?
 Power Conversion  dBm to milliWatts and milliWatts to dBm
Power Budget 
Use this calculator to walk through all the factors that make up your Power Budget. The 'Power Budget' is the the total power being output from the wireless system and is the sum of:
Enter one parameter in each column (or leave blank) depending on what you know and the calculator will supply the appropriate conversions automatically. Up to 2 decimal places may be entered as 0.xx or .xx. Note: Connector loss is generally small UNLESS you've got lots of 'em in which case you are probably in trouble anyway, or your cable is VERY short. Just leave the line blank if you are feeling lazy. Calculations and equations used. 
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. Calculations and equations used. 
Fresnel Zones 
Defines how much clearance you need (yes you need more than simple LineofSight) and for longer links > 3 Km (2 miles) whether you may have a ground clearance problem from our friendly planet. 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 midpoint 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 midpoint), the 60% (no obstacle) radius and the height of the effective earth curvature at the midpoint of the Total link distance using the effective earth radius. Calculations and equations used. 
System Performance 
This calculator will give you one of three answers:
To RESET any parameter just set it to BLANK before clicking 'Calculate' Notes: RX Sensitivity is ALWAYS expressed as a negative dBm ( dBm) and is the lowest power of signal your radio can handle. Its buried somewhere in your radio spec and will be typically in the range of 70 to 110 dBm. Don't guess or 'fudge' this number. Note: If you solve for TX antenna (you leave it blank) and define a specific SAD factor it is applied to the TX budget and any TX antenna value will include this factor. If you then click Calculate again without changing anything, the SAD factor will be calculated to include the supplied TX antenna value and thus may show a lower value than the original one. Calculations and equations used. 
milliWatts to dBm (and vice versa) 
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. 
Power Budget Calculations

mW to dBm = 10Log_{10}(mW)

feet to meters = .3048

meters to feet = 3.28

Calculator normalises all distances to kilometers and meters

Connectors loss = 0.10 * square root (frequency in GHz)
Free Space Calculations

Free space loss = 36.56 + 20Log_{10}(Frequency) + 20Log_{10}(Distance in miles)

Calculator normalises all distances to miles

Miles to Kilometers = 1.609

Kilometers to miles = 0.621
Fresnel Zone Calculations

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) = 72.6 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
System Performance Calculations

Calculator normalises all distances to miles and feet during calculations.

Free space loss = 36.56 + 20Log_{10}(Frequency) + 20Log_{10}(Dist in miles)

mW to dBm = 10Log_{10}(mW)

dBm to mW = 10^{(dBm/10)}

RX Power = Margin  RX sensitivity

Theoretical margin = TX power budget + RX power budget  free space loss

SAD factor = Theoretical margin/TX power budget * 100 and shows the percentage of spare power on transmission.
dBm to milliWatts Calculations

mW to dBm = 10Log_{10}(mW)

dBm to mW = 10^{(dBm/10)}