Wifi Calculator – GudangWireless

Radio system

Key: Green is good, Red is bad.

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:

PLUS Radio Transmit Power (A above)
MINUS cables and connectors losses (B above)
PLUS antenna gain (C above).

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.

Radio and Antenna
Transmit Power	Antenna Gain	Power
mW OR dBm	dB(i)	dB
Cable Loss
Cable Properties (per 100 ft or m)	Cable Length
dB (100 ft) OR dB (100 m)	feet OR meters	dB
Connector Loss
Frequency in MHz	No. of Connectors
MHz.	No.	dB
Budget
		dB

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.

Frequency	Distance		Result
MHz	Km OR Miles		dB

Fresnel Zones

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.

Calculations and equations used.

System Performance

This calculator will give you one of three answers:

If you leave distance blank it will apply the defined SAD factor (or default to 30%) to the Operating Margin and supply the max. distance (in Km and Miles) at which the Margin operates.
If you enter the distance it will calculate the Operating Margin and the SAD factor.
If you enter distance but leave RX or TX antenna gain (or both) blank it will apply the chosen SAD factor (or default it to 30% if none supplied) and generate the required antenna power. If both are left blank it will calculate a symmetrical antenna gain.

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.