Posted by Downlink Link Budget Calculator
Complete Downlink Link Budget Calculator for SATCOM: Calculate satellite EIRP, G/T, path loss, C/N0 & link margin for 11.7 GHz Ku-band GEO downlink.
Complete Downlink Link Budget Calculator
Satellite to Earth Station | EIRP | G/T | C/N0 | Friis | ITU-R aligned
Geometry & Path
GHz
km
deg
dB
Satellite Transmit (EIRP)
dBW
dB
dBW
Typical GEO Ku-band contour EIRP: 42-52 dBW. Ka-band often higher per beam.
Propagation Losses (Ls)
dB
dB
dB
dB
dB
Earth Station Receive (G/T)
m
-
dBi
K
dB
dB/K
Bandwidth & Link Performance
Hz
bps
dB
dB
Key Results
Received Power Pr (Friis)
--
dBW
C/N0
--
dB-Hz
C/N
--
dB
Achieved Eb/N0
--
dB
Link Margin
--
dB
G/T
--
dB/K
Formulas (ITU / Standard Link Equation)
Free-Space Path Loss - ITU-R P.525
Lfs = 92.45 + 20 log10(f_GHz) + 20 log10(d_km) [dB]
Antenna Gain (parabolic)
Gr = 10 log10( eta * (pi * D / lambda)^2 ) [dBi] where lambda = c / f
Figure of Merit
G/T = Gr - Lrx - 10 log10(Tsys) [dB/K]
Received Carrier Power (Friis)
Pr = EIRP_eff + Gr - Ls - Lrx [dBW]
Carrier-to-Noise Density Ratio (canonical downlink equation)
C/N0 = EIRP_eff + G/T - Ls - k where k = -228.6 dBW/Hz/K
Note: the expression C/N0 = EIRP + G/T - Ls - 10log10(B) omits Boltzmann constant k and actually yields C/N, not C/N0.
C/N and Energy-per-bit
C/N = C/N0 - 10 log10(B) [dB]
Eb/N0 = C/N0 - 10 log10(Rb) [dB]
Link Margin = Eb/N0(achieved) - Eb/N0(required) - Implementation Loss
Detailed Link Budget Table
| Parameter | Value | Unit | Contrib. |
|---|
ITU references: Free-space loss - ITU-R P.525; Gaseous absorption - ITU-R P.676;
Rain attenuation - ITU-R P.618 + P.838; Cloud - ITU-R P.840. Full site-specific rain statistics require ITU-R P.837 digital maps. Values above are user-editable engineering estimates.