Empathy List Archives

I

iovane@inwind.it

Wed, Mar 19, 2014 11:46 PM

Those who say the missing aircraft should be searched along the two corridors, what measurement are they relying on? I think it is a one-way measurement of time-stamped pings, which implies good synchronization of clocks between a geosynchronous satellite and a moving aircraft. Antonio I8IOV

BH

Bill Hawkins

Thu, Mar 20, 2014 12:21 AM

They only got one ping from INMARSAT at 64E above the Indian Ocean.
There was no other ping to triangulate the position.

One ping projects a circle on the Earth. The maximum flying range of the
plane determined the ends of the NE and SE arcs of that circle.

The news only gets stranger as time goes on.

Bill Hawkins

-----Original Message-----
From: iovane@inwind.it
Sent: Wednesday, March 19, 2014 6:46 PM

Those who say the missing aircraft should be searched along the two
corridors, what measurement are they relying on? I think it is a one-way
measurement of time-stamped pings, which implies good synchronization of
clocks between a geosynchronous satellite and a moving aircraft. Antonio
I8IOV

They only got one ping from INMARSAT at 64E above the Indian Ocean. There was no other ping to triangulate the position. One ping projects a circle on the Earth. The maximum flying range of the plane determined the ends of the NE and SE arcs of that circle. The news only gets stranger as time goes on. Bill Hawkins -----Original Message----- From: iovane@inwind.it Sent: Wednesday, March 19, 2014 6:46 PM Those who say the missing aircraft should be searched along the two corridors, what measurement are they relying on? I think it is a one-way measurement of time-stamped pings, which implies good synchronization of clocks between a geosynchronous satellite and a moving aircraft. Antonio I8IOV

JL

Jim Lux

Thu, Mar 20, 2014 3:47 AM

On 3/19/14 5:21 PM, Bill Hawkins wrote:

They only got one ping from INMARSAT at 64E above the Indian Ocean.
There was no other ping to triangulate the position.

One ping projects a circle on the Earth. The maximum flying range of the
plane determined the ends of the NE and SE arcs of that circle.

The news only gets stranger as time goes on.

not time based...from what I understand it's based on a received power
estimate, matched against antenna patterns.

Not particularly accurate. The power measurement is probably good to
0.2 dB (at best). If the transmit antenna's attitude isn't in the
nominal straight and level (e.g. plane is banking, or parked on ground,
perhaps with a tarp placed by a overweight gentleman holding a white
furry cat on his lab?)

I did some back of the envelopes and there's a good many 100s of km
uncertainty in range.

On 3/19/14 5:21 PM, Bill Hawkins wrote: > They only got one ping from INMARSAT at 64E above the Indian Ocean. > There was no other ping to triangulate the position. > > One ping projects a circle on the Earth. The maximum flying range of the > plane determined the ends of the NE and SE arcs of that circle. > > The news only gets stranger as time goes on. > not time based...from what I understand it's based on a received power estimate, matched against antenna patterns. Not particularly accurate. The power measurement is probably good to 0.2 dB (at best). If the transmit antenna's attitude isn't in the nominal straight and level (e.g. plane is banking, or parked on ground, perhaps with a tarp placed by a overweight gentleman holding a white furry cat on his lab?) I did some back of the envelopes and there's a good many 100s of km uncertainty in range.

N

nuts

Thu, Mar 20, 2014 4:28 AM

A lot of these satellites have "footprints" for each antenna. I don't
know if the footprints are narrow enough to track a plane.

A lot of these satellites have "footprints" for each antenna. I don't know if the footprints are narrow enough to track a plane.

DI

David I. Emery

Thu, Mar 20, 2014 6:48 AM

On Wed, Mar 19, 2014 at 09:28:38PM -0700, nuts wrote:

A lot of these satellites have "footprints" for each antenna. I don't
know if the footprints are narrow enough to track a plane.

I do believe there is an time offset for each aircraft sent on

the forward control channel from the ground (which is shared with many
aircraft) that allows a particular aircraft to transmit a frame in the
center of its allocated slot. IIRC the ground measures the error and
sends a correction to the plane which allows the plane's transceiver to
compute just when - relative to the system frame timing derived from the
received forward control channel from the satellite - it should
transmit the reverse control channel burst.

--
Dave Emery N1PRE/AE, die@dieconsulting.com DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in
celebration of what could have been, but wasn't and is not to be now either."

On Wed, Mar 19, 2014 at 09:28:38PM -0700, nuts wrote: > A lot of these satellites have "footprints" for each antenna. I don't > know if the footprints are narrow enough to track a plane. I do believe there is an time offset for each aircraft sent on the forward control channel from the ground (which is shared with many aircraft) that allows a particular aircraft to transmit a frame in the center of its allocated slot. IIRC the ground measures the error and sends a correction to the plane which allows the plane's transceiver to compute just when - relative to the system frame timing derived from the received forward control channel from the satellite - it should transmit the reverse control channel burst. -- Dave Emery N1PRE/AE, die@dieconsulting.com DIE Consulting, Weston, Mass 02493 "An empty zombie mind with a forlorn barely readable weatherbeaten 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in celebration of what could have been, but wasn't and is not to be now either."

time-nuts@lists.febo.com

Aircraft ping timing