FSL = 36.6 + 20Log10(FMc.) + 20Lopg10(Dmi)
Where FSL = Free Space Loss in dB
Mc. = Frequency in Mc.
Dmi = Distance in miles
PEL = 10Log10[3.45 x 10-15((Rh x Th)/d2)2]
Where PEL = Plane Earth Loss in dB
P1 = Transmitted Power in Watts
P2 = Received Power in Watts
d = Distance between sites in miles
Rh = Height of receive antenna above ground (ft)
Th = Height of transmit antenna above ground (ft)
SL = 10Log10FMc. + 20Log10Dmi – 10Log10Hft – 55.8
Where Mc. = Frequency in Mc.
Hft = Main obstacle height in feet
Dmi = Shortest distance from obstacle to transmitter or receiver in miles
Radio Line-of-Site = SQRT(2H1H2) x 1.15
Where SQRT = Square Root
H1 = Height of antenna at site 1 in feet
H2 = Height of antenna at site 2 in feet
ERP = GainsdB + LossesdB
Where GainsdB = all system gains in dB (i.e., Tx Power & Antenna Gain)
LossdB = all system losses in dB (i.e., Line Loss, Jumper Cables,Protective Devices, & Lightning Arrestor)
To convert Tx Power to dBm, dBm = 10Log10(P1/P2)
Where dBm = Power in dB reference to 1 milliwatt (mw)
P1 = Transmit power in Watts
P2 = .001 (1 mw)
To convert dBm to Watts, Watts = 10((dBm-30)/10)
Where Watts = ERP in Watts
dBm = ERP in dBm
Meters Feet
lm = 300/Mc. lft = 984/FMc.
Where lm = Wavelength in meters Where lft = Wavelength in feet
Mc. = Frequency in Mc. FMc. = Frequency in Mc.
½l = 150/ Mc. ½l = 492/ FMc.
¼l = 75/ Mc. ¼l = 246/ FMc.
Meters Feet
lm =
285/Mc. lft =
936/FMc.
Where lm = Wavelength in meters Where lft = Wavelength in feet
Mc. = Frequency in Mc. Mc. = Frequency in Mc.
½l = 143/ Mc. ½l = 468/ FMc.
¼l = 71/ Mc. ¼l = 234/ FMc.
Meters Feet
lm = (300/FMc.) x VF lft = (984/FMc.) x VF
Where lm = Wavelength in meters Wherelft = Wavelength in feet
FMc. = Frequency in Mc. FMc. = Frequency in Mc.
VF = Velocity Factor VF = Velocity Factor
½l = (150/ FMc.) x VF ½l = (492/ FMc.) x VF
¼l = (75/ FMc. ) x VF ¼l = (246/ FMc.) x VF
RL = -20Log10(|G|)
Where RL = Return Loss in dB
|G| = Reflection Coefficient
|G| = [ (VSWR-1) / (VSWR+1) ] x 100
Where |G| = Reflection Coefficient
VSWR = Voltage Standing Wave Ratio
VSWR = (1+|G|)/(1+|G|)
Where VSWR = Voltage Standing Wave Ratio
|G| = Reflection Coefficient
VSWR = [SQRT(Fwd) + SQRT(Ref)]/ [SQRT(Fwd) - SQRT(Ref)]
Where VSWR = Voltage Standing Wave Ratio
Fwd = Measured forward transmitter power
Ref = Measured reflected transmitter power
Calculating Received Signal in Free Space
Convert transmit power and receiver sensitivity into dBm; Then have all other units in dB.
Pr = Pt – Lw1 – Lf1 + Ga1 + Lfs + Ga2 – Lw2 – Lf2
Where: Pr = Received power level in dBm
Pt = Transmit power level in dBm
Lw1 = Transmit site transmission line loss in dB
Lw2 = Receive site transmission line loss in dB
Lf1 = Transmit site filter/miscellaneous losses in dB
Lf2 = Receive site filter/miscellaneous losses in dB
Lfs = Free Space Path Loss in dB
Ga1 = Transmit antenna gain in dBd
Ga2 = Receive antenna gain in dBd
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