Satellite Link Budgets index page
Link budgets index page

Satellite beam design

Satellite downlink EIRP

Uplink satellite G/T

Uplink PFDsat

Antenna beam width calculator

Views of the earth from various orbit positions

VSAT network design

View Planet Earth

dB to watts calculator

Example Satellite Link Budget Calculator

Complete all boxes in the white rows and then click any calculate button to obtain results in the green rows.

Uplink frequency GHz
Uplink antenna diameter m
Uplink antenna aperture efficiency e.g. 0.65
Uplink antenna transmit gain dBi
Uplink antenna, power at the feed W
Uplink EIRP dBW
Range km
Uplink path loss dB
Uplink pfd at satellite dBW/m^2
Bandwidth Hz
Satellite uplink G/T dB/K
Uplink C/N dB

Downlink frequency GHz
Downlink receive antenna diameter m
Downlink receive antenna aperture efficiency e.g. 0.65
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

Note that this is just a simple example to get you started.

Uplink from teleport hub earth station to satellite

If your input data is earth station uplink gain, then input the uplink frequency and a dish size and adjust the dish size to get the transmit gain as you want it.

If your input data is transmitter power in watts, use that figure. If your input data is transmitter power in dBW, the calculate the watts manually and put the watts value in the box.

You will need more power proportional to greater bandwidth operation.

You might use a 100 watt transmit amplifier and transmit only 25 watts in clear sky and increase to 100 watts in heavy rain. This is called 6 dB of uplink power control, based measurement of the satellite beacon on the downlink, plus a calculation.

Range: Many recent satellites operate in low (under 2400km altitude) or medium height orbits. Geo orbit is 35786 km altitude.  Calculate the actual slant path range for higher accuracy.

Input the carrier bandwidth in Hz. This can be anything for a few Hz to several hundred MHz.  Satellite transponders may be 36, 55 or 236 MHz (for example) wide.  Carriers from a few Hz to 36 MHz typical. You decide.

You get the satellite uplink G/T towards your uplink site by looking at the satellite beam uplink coverage map contours. If you are designing the satellite then make a suitable coverage beam, work out its gain according to coverage area diameter and height. Use something like 450K as the system noise temperature as the beam looks at the warm ground.  Take off 4 dB, if working at the beam edge (-4 dB down contour).

Uplink C/N: If your uplink site is main teleport then you will probably make this high, like 20 - 25 dB. If your uplink is some tiny remote terminal then you will be looking for an uplink C/N of 12 dB if possible. 

Downlink from satellite to customer earth station.

Here is your chance to try your own ideas.

The downlink earth station receive antenna system noise temperature is mainly the earth station LNA (say 150K - 200K), as the background is cold space.

The resulting C/N affects the number of bits/Hz that you can get using various modulation and coding techniques (MOD/COD). The number of user bits/Hz varies from about 1 to 3.5, with higher figures possible for very high overall C/N values. See modem spec sheets.

Have a link margin of several dB (say 3 -5) for miscellaneous degradations. 

During heavy rain fading, reduce the user bit rate by 2 to 4 times to keep some kind of customer service going.

Downlink EIRP: Find out from the satellite operator what is the maximum downlink EIRP on the various beam coverage contours. Note the value for your downlink site location. This is the EIRP for a whole transponder (say 36 MHz) operated with a single big carrier. If in multi-carrier mode then the satellite amplifier will be backed off a bit to reduce intermodulation to about 21 dB. Backoffs of several dB are typical, with 1.5 dB for satellite amplifiers with linearisation.  If your carrier is 1 MHz  wide in a 36 MHz transponder then your downlink EIRP is reduced further by 10log(1/26), as you normally get your fair share of the total power unless you pay more.


At the top of this web page is a link to "Link Budgets index page". This leads to pages with pre-calculated satellite link budgets with useful default parameters inserted which may be amended and then recalculated.

Any problems, comments or suggested amendments please e-mail me: Eric Johnston

► Page started 28 June 2023, Amended 29 June 2023

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