FlightAware Discussions

How does MLAT work?

Mode S transponders transmit on 1030 Mhz. ADS-B receivers like the PIAware have only 1090Mhz receivers. How does MALT work when the receivers can not even receive the frequency that the transponders are transmitting on?

Mode S transponders don’t transmit on 1030 MHz, they transmit on 1090 MHz. 1030MHz is the uplink frequency used by ground stations to interrogate aircraft.


The Air Traffic Control Radar Beacon System (ATCRBS) and the
Mode Select (Mode S) system have a ground-based and airborne component and operate
on the frequencies of 1030 MHz and 1090 MHz.


The interrogation y ATC radar is done on 1030 MHz, the transponder then responds on 1090 MHz.

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MLAT is similar to how GNSS/GPS works.Both use trilateralisation
You have several known ground location. Each ground location gets timing information from specific ADS-B signals. The MLAT servers use this timing information to work out the location of aircraft that are not transmitting position information.
With MLAT the receiving locations are known. With GNSS/GPS the satellite locations are known. GNSS/GPS use much larger distances, however, the clocks are better.

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