said by TomS_:
In the case of an Internet service which is two way, Im not exactly sure how the return path is handled. It would likely be done with a second transponder, but Im not 100% sure.
For example with HughesNet on G3c where HughesNet has only a single horizontal transponder, subscribers will receive a download stream on 12.110 Ghz horizontal and will transmit an upload stream 14.410 Ghz horizontal.
Likewise the NOC will transmit up to the bird on 14.410 H and receive 12.110 H.
The transponder which is number 21 simply receives the signal and using an IF of 2.3Ghz block converts and amplifies and then downlinks what it receives.
Satellites on the uplink/downlink RF side are really dumb devices utilizing basic block convertors to do the frequency transconverting, they dont do any error correction or frequency correction other than the IF reference on board.
Its KISS at its best.