Downlink is a communication link between a satellite and a ground station. In general, downlink contains HM data and payload related data primarily.

==Flow of Data for Downlink ==

# '''Acquisition and Encoding of data:''' Different types of data gathered by the OBC which need to be transmitted to the ground-station. Further, this data needs to be encoded/packeted.

# '''Modulation of data:''' Now this data needs to be modulated on the desired carrier frequency.

== Case Study - Pratham ==

In Pratham, the on-board computer (OBC) gathers HM data from various sensor readings and stores it in the on-board memory. The OBC microcontroller accesses this data and packets it using AX.25 protocol and pushes it towards the downlink board microcontroller. On the downlink board, we have the CC1101 transceiver which gets data from downlink board microcontroller and then modulates it on the carrier frequency using 2-bit FSK modulation scheme. Now for conditioning, we amplify the signal gain using RF5110G Power Amplifier and then transmit the signal using monopole antenna onboard the satellite to ground. <br \>

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