Link budget index
Link budgets index

VSAT information

Latitude and longitude explanation

Link budget calculator

Satellite beam design

Hub to remotes outlink (downstream) link budget

Uplink power control UPPC

Broadband satellite internet in Middle East

Antenna beam width calculator

Views of the earth from various geo orbit positions

Explanation of satellite links

EbNo measurement and EbNo Calculator

9600 bps return links

Link Budget for return links from VSAT remote sites to the HUB: Upstream

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


Return links from VSATs to the hub are expected to comprise a variety of small TDMA carriers with QPSK 3/4 rate FEC such as:
210kbit/s   140 ksps burst carriers with 168 kHz noise bandwidth and 200 kHz spacing.
420kbit/s   280 ksps burst carriers with 336 kHz noise bandwidth and 400 kHz spacing.
840kbit/s   560 ksps burst carriers with 672 kHz noise bandwidth and 800 kHz spacing.

All remote sites are within the uplink contour of +6 dBK and transponder gain step is set to PFDsat=-96 dBW/m2

The transponder multi-carrier operating point is -7 dB in and -2 dB out.  C/Intermod = 21 dB at this point.

Assuming whole transponder is filled with 180 carriers, each with 200 kHz allocated bandwidth. Or any other combination of carriers of various sizes.

Total power spectral density produced at the satellite of all carriers combined is -96 -7 = -103 dBW/m2

Saturated downlink EIRP towards the hub site = 54 dBW.

Operating PFD produces a total downlink EIRP = 54 - 2 = 52 dBW

This conversion (-103 in and + 52 out) has been put into the link budget. It applies to multi carrier operation.

The remote site transmit BUC is 2 watt, operated at 0.25 W in clear sky conditions with 210 kbit/s carrier or 0.5W with 420 kbit//s carrier.   Note 0.25W x 180 = 45W

If a half transponder is leased the capacity is 210 x 90 carriers = 18.9 Mbit/s. This might in practice allow about 10 Mbit/s through, complementing a 40 Mbit/s outlink.

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.

Any problems or comments please e-mail Eric Johnston

Copyright (c) 23 Feb 2012 Satellite Signals Ltd All Rights Reserved
Last Revision: 6 April 2021.