You are here:

# Satellite Communications/Calculate Required Transmit Power

Question
QUESTION: Hi Luis,

I found this example on Dave's page to calculate the Transmit Power Required in case SFD and Antenna Gain are known. Can you reconfirm if this calculation is correct and help me understand also. Since Dave is not available, I am sorry to bother you.

Thanks and Kind Regards
Ejaz Ahmed

For example
•   d = 36636 km
•   SFD = - 90 dBW
EIRP = 10.log(4.π.36636.10³) – 90 = 72.3 dBW

indeed,
EIRP = SFD + atmospheric losses + 10*log10( 4Pi* distance to satellite in meters)
note that atmospheric losses in clear sky should be calculated and could be relevant particularly for high frequency links at low elevation. and this losses are not the free space loss.

so the only thing you are missing are propagation losses.

---------- FOLLOW-UP ----------

QUESTION: Hi Luis,

First of all, thanks a lot for your prompt response. I just need your help once again. Can you further guide on the calculation of Atmospheric Losses also in Ku-Band.

Best Regards
Ejaz Ahmed

Hi,
atmospheric losses are caused mainly by the presence of gases and hydrometeors in the atmosphere. these losses are a function of frequency and the calculation is described in detail in the ITU-R recommendations of the P series (propagation)

there are a few calculators online,

try for example

http://www.vk3um.com/index.html

or

http://descanso.jpl.nasa.gov/Propagation/propagation.cfm?force_external=0

the last link also has some books that can guide you through understanding each of the impairments.

but for Ku band, elevations > say 20 degrees, you are looking at a small component in clear sky, about 1 to 1.5 dB ...

Satellite Communications

Volunteer

#### Luis Emiliani

##### Expertise

Strengths - Satellite link design and analysis - Vsat network design and analysis - Propagation aspects for terrestrial and satellite links - ITU-R P recommendations Can not help with: - Questions related to TV receivers, TV kits, or specific networks such as DirecTV or DISH - Antenna pattern synthesis, RF MoM analysis, S-parameters.

##### Experience

My experience is in satellite communication networks and terrestrial microwave links.