Malaysian Airlines MH370 contact lost

[RichManJoe]

Possible INMARSAT rf processing

I am not knowledgeable about the rf front end for the INMARSAT, but I am knowledgeable about AEHF and a few other communication satellites, and I would hypothesize they are similar. The comms between the satellite and the ground terminals (in this case, the aircraft terminal node controller (TNC)) use a form of PSK. All of the baseband and "IF" processing is done synchronously using digital processors, so there are digital to analog (D/A) converters prior to the upconverters and A/D's immediately following the downconverters. I don't know what the state of technology is today, but the converters may be sampling on the order of 400 MSPS to 1GSPS. For the receiver, the first digital process which is performed following the A/D is a fast fourier transform to channelize the data. This is then followed by a phase lock loop (PLL), which removes the doppler. By simply logging this phase correction used in the PLL (simply a number indicating radians per sample period) and sending it in the downlink to the INMARSAT earth station in Australia, INMARSAT would be able to reconstruct the doppler. This may be normal payload telemetry.