dBm to Watt Conversion Table

dBm is normally use in WiFi technology for signal calculation. WiFi device must follow country guidelines available for 2.4Ghz Signal strength. In Malaysia base on MCMC Wireless Lan Service Guideline (MCMC/G/01/05-WLAN) each station only allow maximum Effective Isotropic Radiated Power (EIRP) of 500 miliWatts (2.4-2.5Ghz Frequencies).So effectively 500mWatt equal to 27dBm maximum EIRP allowed in Malaysia.

EIRP = Pout - Ct + GtDefinition :Pout : transmitter power output (dBm)Ct : signal loss in cable (dB)Gt : gain of antenna (dBi)

Effective Isotropic Radiated Power (EIRP)EIRP = Pout – Ct + GtEIRP = Effective Isotropic Radiated Power (dBm)Pout = transmitter power output (dBm)Ct = signal loss in cable (dB)Gt = gain of the antenna (dBi)The maximum EIRP for Class Assignment Wireless LAN type devices;

Frequency Bands Max EIRP(Watts)

Max EIRP(dBm)

1. 2400 MHz to 2500 MHz 500 milliWatts 27 dBm

2. 5250 MHz to 5350 MHz 1 Watt 30 dBm

3. 5725 MHz to 5875 MHz 1 Watt 30 dBm

Sample EIRP Calculation : Case 1

The EIRP calculation;EIRP = 20 dBm – 0 dB + 7 dBi= 27 dbm @ 500 milliWattsThe usage of the 2400 MHz Wireless LAN device with a 7dbi antenna iswithin the allowed maximum EIRP which is at 500 milliWatts.

Sample EIRP Calculation : Case 2

The EIRP calculation;EIRP = 20 dBm – 3 dB + 10 dBi = 27 dbm @ 500 milliWattsThe usage of the 2400 MHz Wireless LAN device is within the allowedmaximum EIRP which is at 500 milliWatts .

Sample EIRP Calculation : Case 3

The EIRP calculation;EIRP = 20 dBm – 3 dB + 16 dBi = 33 dbm @ 2 WattsThe usage of the 2400 MHz Wireless LAN device exceeds and breachesthe allowed maximum EIRP which is at 500 milliWatts. Users have toeither reduce the Pout or use lower gain antenna to meet the maximumallowed EIRP.

Wifi Calculator : Signal Link Budget

Hi everyone... today i will teach simple WiFi signal calculation to determine if the connection between access point station and client can be succesfuly done.

Formula :

1) Signal Receive by AP = AP Antenna Gain + [C Tx Power + C Antenna Gain] - [Distance Signal Lost]

2) Signal Receive by C = C Antenna Gain + [AP Tx Power + AP Antenna Gain] - [Distance Signal Lost]

Definition : AP = Access Point ; C = Client

There is 3 factor can effect the signal receive by the access point and client side.1. Access Point Station : Antenna Gain, Tx Power & Minimum Sensitivity2. Client : Antenna Gain, Tx Power & Minimum Sensitivity3. Enviroment : Distance

1) Example :Access Point :- Tx Power : 50 mWatt = 20dBm- Minimum Sensitivity : -93dbi- Antenna Gain : 10dbiClient :- Tx Power : 50mWatt = 17dBm- Minimum Sensitivity : -75dBi- AntennaGain : 2dBiDistance : 1000meter = -100.1dBi

1) RX AP = 10 + 17 + 2 - 100.1 = -71.1dBi2) RX C = 2 + 20 + 10 - 100.1 = -68.1dBi

Conclusion:- Access Point Side : Signal Receive is -71.1dBi, more than the minimum of -93dBi, which mean the Access Point can receive signal from Client succesfully- Client Side : Signal Receive is -68.1dBi, more than the minimum of -75dBi, which mean the Client can receive signal from Access Point succesfully.- Connection between Access Point and Client can be done without signal problem. :)

2.4Ghz WiFi Channel Infrastracture

WiFi IEEE 802.11b has a very limited channel (depend on country). In very pack area with many WiFi Access point not all channel can be use at the same time. In North America, US State and Canada only Channels 1,2,3,4,5,6,7,8,9,10 and 11 are available for usage. In Europe Channel 1,2,3,4,5,6,7,8,9,10,11,12 and 13 can be use. In Japan only Channel 14 available for usage. The usage of each channel depend on country policy.

WiFi with base protocol IEEE 802.11b used Direct Sequence Spread Spectrum (DSSS) Modulation, which mean spectruam width for each usage is 22MHz wide for each station. This mean a station with 2437MHz Channel will be working on frequencies range of 2426MHz to 2448MHz. It will interfere 2 channel below and up of its channel. So effectively only 3 channel can be used without interfering each other which is Channel 1 , 6 and 11.

Channel : Frequency (Bold Channels = Recommended)

1 : 2412MHz2 : 2417MHz3 : 2422MHz4 : 2427MHz5 : 2432MHz6 : 2437MHz7 : 2442MHz8 : 2447MHz9 : 2452MHz10 : 2457MHz11 : 2462MHz12 : 2467MHz13 : 2472MHz14 : 2477MHz