From: Hal Murray
There is a newer system getting phased in: ADS-B
http://en.wikipedia.org/wiki/Automatic_dependent_surveillance-broadcast
The plane broadcasts it's position and velocity every second.
The SDR folks are having fun with it. With one of the USB TV receiver
gizmos
and a Raspberry Pi, you are limited by the height of your antenna vs
curvature of the earth. A friend with an antenna 20(?) feet up gets planes
out to several hundred miles. I don't know how far it will work if you have
an antenna on top of a hill.
http://www.rtl-sdr.com/adsb-aircraft-radar-with-rtl-sdr/
==========================
.. and by sharing this data on a central server you can overcome the
line-of-sight limitation:
http://www.satsignal.eu/raspberry-pi/dump1090.html
There is a further development which may be of interest to the more
mathematically oriented time-nuts, creating positions of aircraft which do
no send out their position with ADS-B but use earlier responses. By
comparing the timing of responses from aircraft which do send position with
those that don't you can multilaterate a position for the position-less
aircraft. This requires timing in the receiver device to a level of about
100 nanoseconds, most often achieved with a simple crystal oscillator (but
which needs calibration). In the DVB-T sticks the usable sampling rate is
about 2 MHz, and the resulting 500 microsecond resolution appears not to be
good enough for even a basic multilateration fix.
If anyone is interested further or could help with suggestions on improved
accuracy with the DVB-T sticks, a suitable place would be the Plane Plotter
Yahoo group:
http://groups.yahoo.com/group/planeplotter/
Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: [email protected]
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