[time-nuts] MH370 Doppler
jleikhim at leikhim.com
Tue Aug 19 12:08:24 EDT 2014
My understanding is that the BFO and BTO values are self reported from the SDU (Terminal in the aircraft) and they represent adjustments made by the SDU. If so the BFO value would be the AFC adjustment relative to the OCXO onboard. My contention is that if the investigators are assuming the OCXO is 2Hz high and reporting an +88Hz offset as 86Hz Doppler, what if in fact the OCXO is 10Hz high? Then the doppler is 78Hz and that means the velocity and location at each of the pings is way off.
It would also be good to know if the terminal has any sort of holdover battery to keep it running. So far I have heard only that the IRU has battery. Even so, the terminal has possibly three power sources, left and right and APU busses. Unlikely as it seems, what if they ditched successfully at sea and the APU ran for hours?
From: "David I. Emery"<die at dieconsulting.com>
"IIRC the plane is expected to adjust its burst uplink frequency
and timing to come out right at the satellite receive antenna... thus
compensating for the uplink Doppler at L band and the time delay too.
But I do remember that the ground supplies feedback on the control
channel as to how much the plane is off so it can adjust...
Guess it might be time to dig out the docs again."
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JLeikhim at Leikhim.com
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