written 5.6 years ago by | • modified 5.6 years ago |

**Subject :** Satellite Communication and Networks

**Topic :** Satellite Links

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What is EIRP ? Discuss the importance of G/T ratio. Calculate overall C/N for a satellite link if : C/N uplink = 25db , downlink = 20db and Intermodulation = 12db.

written 5.6 years ago by | • modified 5.6 years ago |

**Subject :** Satellite Communication and Networks

**Topic :** Satellite Links

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written 5.6 years ago by | • modified 5.6 years ago |

Effective isotropic radiated power (EIRP) is defined as an equivalent transmit power and is given as

$EIRP = Pt Gt$

Where $Pt = \text{transmitted power}$

$Gt = \text{transmit antenna gain}$

Express as log

$EIRP(dBW)=Pt(dBW) + Gt(dB)$

In respect to transmitter output

$EIRP = Pt - B0 - Lf + Gt$

Where $B_0 = \text{Back off of HPA (dB)}$

$L_f = \text{total branching and feeder loss}$

**Importance of G/T ratio:**

The antenna gain to noise temperature ratio is a figure of merit to indicate the performance of the earth station antenna and the low noise amplifier in relation to sensitivity in receiving downlink carrier from the satellite.

The parameter G is the receive antenna gain referred to the input of the low noise amplifier.The parameter T is defined as the earth station system noise temperature referred also to the input of the low noise amplifier.

Figure of merit is widely used to characterize a satellite receiving system.The higher the value of figure of merit, the better will be the system.Figure of merit of a typical satellite receiving system is about - $8 db/K$

$\begin{aligned} \big( \frac{C}{N} \big)_U &= 25 db \\ \big( \frac{C}{N} \big)_D &= 20 db \\ \big( \frac{C}{N} \big)_{JM} &= 12 db \\ \therefore \big( \frac{C}{N} \big) &= \frac{1}{ (\frac{C}{N})_u^{-1} + (\frac{C}{N})_D^{-1} + (\frac{C}{N})_{JM}^{-1} } \\ &= \frac{1}{ (10^{2.5})^{-1} + (10^{2})^{-1} + (10^{1.2})^{-1} } \\ &= 13.11 \end{aligned}$

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