Satellite Communications/D/L EIRP

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Question
QUESTION: Hai rao,

Let us say I have one characterized antenna & pointed to SAT (i.e G/t & EIRP is known), then We are up-linking signals & monitored on same antenna using spectrum analyzer..

How i can measure / calculate Downlink EIRP if i don't have space segment details like SFD / EIRP & Back off of SAT etc... ???

Regards
MS RAO

ANSWER: Hi Mr Srinivasa Rao,
If you are up linking from an Antenna and monitoring your signal: if it is a modulated signal then it is difficult to establish link budget for unknown satellite parameters. However, every satellite is provided with a Beacon  i.e., unmodulated single frequency output signal for tracking purpose. If you calculate the received signal strength and measure C/N with SA and going through iteration backwards we can arrive at downlink EIRP. But this does not give any other info on OBO or IBO etc. Try the SA measured power retrofit and arrive at the solution.
You can contact me for any other clarification in this regard and tell me whether this answer is able to clarify you query.
Cheers/GTRao

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

QUESTION: Yes, I can fire CW carrier from the site... & monitor this CW on the D/L chain using SA....

Without using any details of space segment details? Can you Give some way / procedure to calculate D/L EIRP with C/N & Can i know is it power limited or Bandwidth limited ???

Regards

Answer
You are not allowed to uplink any carrier or signal from any Earth Station to the satellite you are pointing at: You basically need to get your ES qualified by Satellite Operator who sets certain terms and conditions to access transponders. If you are eligible service provider then you automatically have the Satellite specifications with you. So your question is irrelevant in terms HOW TO MEASURE SATELLITE PARAMETERS WITHOUT THE KNOWLEDGE OF THE OPERATOR seems to be out of consideration. Just by making a loop measurement of uplink which means you have to access the transponder/s is not possible.
Bandwidth and Power limited cases can be determined from IBO and OBO and not just by seeing SA measurements. Different satellite have different specs and for doing any measurements we need to be cooperative with the Sat Operator, no other way or procedure.
What I wrote in my earlier reply was one way measurement for understanding the down link EIRP and that does not require uplinking FIRST. And it is one of the measurement techniques to align the ES Antenna to the direction of correct satellite and proving the Link Budget Estimates.
Cheers/GTRao

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TIRUMALA RAO G

Expertise

Satellite Communications Applications, Link Calculations, Teleports, Earth Stations,VSAT, Tracking, Mobile Communications, Next Generation Networks.

Experience

40 Years. Indian Space Research Organisation, PANAMSAT, Satellite Based VSAT Networks, IP Networks.

Organizations
ISRO, PANAMSAT, Engineering Institution for Higher Education (GVP College of Engineering), Consultancy.

Education/Credentials
Graduate in Electronics and Communication Engineering with Distinction. Guiding scholars for their Doctoral thesis in related areas in Academics.

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