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Explanation of satellite links

Symbol rate

EbNo measurement and EbNo Calculator

Link Budget VSAT outlink link from Hub to remote sites: Downstream.

Uplink frequency GHz
Uplink antenna diameter m
Uplink antenna transmit gain dBi
Uplink antenna, power at the feed W
Uplink EIRP dBW
Range (35778 - 41679) km
Uplink path loss dB
Uplink pfd at satellite dBW/m^2
Bandwidth Hz
Satellite uplink G/T dB/K
Uplink C/N dB
Transponder "gain" input PFD to output EIRP
Downlink frequency GHz
Downlink receive antenna diameter m
Downlink system noise temperature(antenna+LNA) K
Downlink receive antenna gain dBi
Downlink receive antenna G/T dB/K
Downlink satellite EIRP dBW
Downlink path loss dB
Downlink C/N dB
Uplink C/interference dB
Uplink C/N dB
Satellite C/intermod dB
Downlink C/N dB
Downlink C/interference dB
Total link C/N dB


The outlink comprises a single carrier occupying a full 36 MHz transponder.

Symbol rate 30 Mbsps

Uplink G/T contour at the hub is +6 dBK and transponder gain step is set to PFDsat=-86 dBW/m2 on the same uplink pfd contour over the site.

The single carrier transponder operating point is -1 dB in and -0.5 dB out.  This is about optimum for higher order modulation methods like 8-PSK and 16-QAM.

So the power spectral density at the satellite needs to be  -86 -1 = -87 dBW/m^2.  Adjust your HPA power and uplink dish size to achieve this.

Saturated EIRP towards the edge of beam remote sites = 51 dBW.

So operating PFD is a downlink EIRP = 51 - 0.5 = 50.5 dBW

This conversion (-97 in and + 50.5 out) has been put into the link budget as the Transponder "gain". It applies to single carrier operation.

The input figures are all guesses and estimates.  You need to overwrite the figures with your own assumptions.

Amend any white boxes and then click the calculate button to obtain results in the green boxes.

A carrier with symbol rate = 30 Msps would provide a data rate of 45 Mbit/s assuming QPSK and 3/4 rate FEC..

If you use a DVB-S2 type outlink with 8PSK or less FEC, the customer information bit rate capacity increases, but the required C/N increases also. This may be possible with higher power satellite or larger customer receive dishes.

Any problems or comments please e-mail me

Copyright (c) 23 Feb 2012 Satellite Signals Ltd All Rights Reserved
Last Revision: 10 April 2020