Link Budget Calculation Marco Zennaro [email protected] Carlo Fonda [email protected] Link Planning How long can a wireless link be? How much power can we use? What kind of antennas should be use? Do the connection cables effect the link? What is the effect of trees? dB math decibels are a relative measurement unit unlike the absolute measurement of milliwatts on the logarithmic scale, the reference cannot be zero because the log of zero does not exist! log(0) is undefined! dB math the reference point that relates the logarithmic dB scale to the linear watt scale is: 1 mW = 0 dBm the m in dBm refers to the fact that the reference is 1 mW and therefore a dBm measurement is a measurement of absolute power dB math to convert mW to dBm: P(dBm)= 10 log P(mW) to convert dBm to mW: P(mW)= log-1 (P(dBm)/10) the advantage of using dB is that gains and losses are ADDITIVE dB math gain or loss in an RF system may be referred to by absolute power measurement (10W of power) or by a relative power measurement (half of its power) -3dB = half the power in mW +3dB = double the power in mW -10dB = one tenth the power in mW +10dB = ten times the power in mW dB math for example: 10 mW + 3 dB = 20 mW 100 mW - 3dB = 50 mW 10 mW + 10 dB = 100 mW 300 mW - 10 dB = 30 mW ! ! "#$%&'(!)!*!+,!,-./$0'.&$12!!!!!" 345!06!7!45/8!!!455!069! ! "#$%&'(&)*+!,-.!/0!12))!/&3'&4(&!56&!1455!%4)7&!5#!#$&!5&$56!#8!5645!%4)7&9! ! 3:55!06!;!45/8!!!:5!069! ! :6&(&!'7)&(!12))!4))#1!4!;723<!34)37)452#$!#8!=2))21455!>#1&'!)&%&)(!16&$!?2%&$!>#1&'! )&%&)(+!?42$(+!4$/!)#((&(!2$!/0=!4$/!/0@!!A2?7'&!B@-C!(6#1(!5645!56&!'&8&'&$3&!>#2$5!2(! 4)14*(!56&!(4=&+!D75!>#1&'!)&%&)(!34$!=#%&!2$!&256&'!/2'&352#$!8'#=!56&!'&8&'&$3&!>#2$5! /&>&$/2$?!#$!16&56&'!56&*!'&>'&(&$5!4!>#1&'!?42$!#'!)#((@! dB !math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dB math for example: +43 dBm 43dB = 10dB + 10dB + 10dB + 10dB + 3dB 1 mW x 10 = 10 mW 10 mW x 10 = 100 mW 100 mW x 10 = 1000 mW 1000 mW x 10 = 10000 mW 10000 mW x 2 = 20000 mW = 20 W dB math exercise: express -26 dBm in Watts -26dB = - 10dB - 10dB - 3dB - 3dB 1 mW / 10 = 100 μW 100 μW / 10 = 10 μW 10 μW / 2 = 5 μW 5 μW / 2 = 2.5 μW dB math when quantifying the gain of an antenna, the decibel units are usually represented by dBi the i stands for isotropic, which means that the change in power is referenced against an isotropic radiator an isotropic radiator is a theoretical ideal transmitter that produces an e.m. field in all directions with equal intensity at a 100% efficiency other decibels units are also used, as for example the dBd which is a measure of the gain of an antenna system relative to a dipole antenna antenna gain an antenna element is a passive device the antenna can create the effect of amplification by virtue of its physical shape by intentional radiator we mean the RF device and all cabling and connectors up to, but not including, the antenna !"###!"#$%&'()(*(+,(,-./#0&.%#12( ! $%&'%%(#)(*%# ! 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(+''+*$%%2!01-(!%,&!5-##&5%-1!$%!%,&!$#%&##$7!!8,&!/-*&1!$%!%,&!+#%&#%+-#$'!1$3+$%-1!*-.'3! ;&!ND!(+''+*$%%27!!"2!$#!$3(+#+2%1$%-1:!+%!+2!4-.1!1&2/-#2+;+'+%4!%-!.#3&12%$#3!%,&!=KK! intentional radiator any reference to “power output of the Intentional Radiator” refers to the power output at the end of the last cable or connector before the antenna for example: if a 30 mW transmitter loses 15 mW of power in the cables and another 5 mW in the connectors, the power of the intentional radiator is 10 mW intentional! radiator! "#$%&'(!)!*!+,!,-./$0'.&$12!!!!"# $%&'()#*+,"# 3$0%1'!45('1'22!678!9:.;5<-($&5:.# ! >:5.&!7 >:5.&!? 9$=1' 799'22!%:5.& 9:..'9&:( 9:..'9&:( 9$=1' $.&'..$ 9:..'9&:( >:5.&!" >:5.&!@ ! ! ! !!!-../00#12345## 12345#-###12345#6###12345#7###12345#8# ABB!0C! ! DE!/?! !!!!!DE!/?!!!!!!!DE!/?! FA)!/?5! G! ABB!0C! ! !)! !!!!!!)! !!!!!!!!!!)! HI)!I)!I)!I)J! G! ABB!0C! ! !)!!!!!!!!!!!!!!)! !!!!!!!!!!)! IAK! G! LB!0C!! ! ! !!!!!!)! !!!!!!!!!!)! IAK! G! )L!0C!! ! ! ! !!!!!!!!!!)! IAK! 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EIRP the EIRP is the Equivalent Isotropically Radiated Power EIRP is the power actually radiated by the antenna element and is important because it is regulated by the FCC or other regulatory agency it is used in calculating whether or not a wireless link is viable ! ! 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