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Satellite Communications/Multicarrier Transponder in VSAT

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Question
Hi

With reference to VSAT operations on a single satellite transponder of 36MHz (or any fixed BW), where a Forward Carrier (Hub) is transmitting to remote VSAT terminals and the remote VSAT terminals are sending Return Carriers on the same downlink transponder, if the transponder is operated in a FIXED GAIN MODE, what will happen if the uplink Forward carrier is increased by +3dB to compensate for uplink rain fade?

The transponder is operated in 24MHz in the forward and the remainder of the bandwidth (~12MHz) is operated as a return carrier, and all remote terminal are fixed without any way to increase its uplink power.

Thanks.

Answer
Hi Mr wh,
Your query is confusing in the sense that transponder bandwidth and signal powers are calculated based on link equations but not on Hub or VSAt powers alone. Also the transponders have certain specifications for Up and Downlinks. Considering the technical parameters, link budgeting is done based on what type of modulation scheme is used and what is the Multiple access used: it is bot available bandwidth and forward or reverse. All power output is available from a transponder irrespective of multi carrier or single carrier, the difference being, we have to give a back off for multi carrier operation in uplin. And the rain fade compensation is done usually at Earth station and not the transponder gain adjustment.
This is the only clarification I can give interpreting your query.
Cheers/GTRao

Satellite Communications

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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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