mm43 noted:
Other than ACARS messages that indicate the SATCOM ANT was still locked to the satellite at 0214z, and the rejected attempts by AF447 to log on to DAKAR ATC, the only other recorded contact with the A/C was the last squawk received at 0148z when approx 250NM from SBFN secondary radar.
ACARS is a VERY low bandwidth operation. It does not need any appreciable power. Nor does it need an aimed antenna to transmit data to a satellite, even in a Clarke orbit. It needs a little more than the 5 watt hand held equipment used by some ham radio operators in coordinated demonstrations with ham radio operators on the ISS for voice communication demonstrations.
The distance is greater. That would require more power. The data bandwidth is much smaller than the FM voice. That would require less power. It's not quite a wash. An omnidirectional antenna is not necessarily needed. Several ACARS-like systems exist in the Maritime service that use virtually handheld sized equipment with omnidirectional antennas to talk to geosynchronous satellite with a data rate running below a couple hundred bits per second.
Therefore requiring the antenna to be "aimed at the satellite" is pushing my credibility limits. Even if there is only one satcom antenna I more than one or two people here know whether the ACARS transmissions use the SAME satellite. And if not it's as easy to shift a steered phased array antenna to omnidirectional to reach the ACARS bird as it is to try to aim at it.
This list is full of people asserting the SatCom antenna is fully aimed with a narrow beamwidth to reach the satellite for ACARS transmissions AND people who assert equally strongly that ACARS uses an omnidirectional antenna, which apparently must be part of the one antenna labeled SatCom aboard the aircraft.
So I simply contend that if thei aircraft entered an out of control spin we do not know when within at least 4 minutes since we do not know beyond a doubt whether the antenna is omnidirectional or not.
The one or two people here who DO know must be terribly frustrated with those asserting otherwise. Hopefully this clears up why some people are still asserting both positions as of the last time I presumed the antenna was directional after getting screamed at for presuming it was omnidirectional.
I do know, beyond any doubt, that I can communicate with a satellite with a device smaller than an iPod at a sufficiently low data rate. I designed the famn dool thing in 1978 for an unnamed agency through a cutout agency.
JD-EE (We all knew who. And it had a TLA in the US.)