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  • Data Question

    Looking at the data table on the Dump1090-fa screen I see the data in the attached image

    According to the key at the bottom most data is ADS-B which I expect as I have an ADS-B receiver, however the blue highlighted data is shown as Other.

    Where is this data coming from, and why is the speed and heading data missing?

  • #2
    Mode-S
    The under-laying technology within ADSB (adsb isn't a thing, but more a term covering many broadcast technologies used)

    The diffeence, is no GPS input for position data.

    https://en.wikipedia.org/wiki/Second...e_radar#Mode_S

    The dead giveaway is the heading at the top total vs 'with positions'
    Posts not to be taken as official support representation - Just a helpful uploader who tinkers

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    • #3
      OK Thanks!
      So the Mode-S data is still transmitted using the same transmitter/frequency/coding as the ADS-B data... just not connected to a GPS?

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      • #4
        Yes. More or less:

        Mode-C = signal from spinning SSR at airport, triggers reply from aircraft (we dont see)
        Mode-S = Broadcasts out without interrogation FROM aircraft - HEX code assigned, transmits Alt/Speed
        ADSB = Mode-S+GPS (mode-s Extended Squitter (more data))

        http://web.mit.edu/6.933/www/Fall2000/mode-s/today.html
        Posts not to be taken as official support representation - Just a helpful uploader who tinkers

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        • #5
          Mode-S and Mode-C transponders are both interrogated by radars.
          Mode-S transponders will also send out extra DF11 messages without interrogation (squitter).

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          • #6
            OK thanks very much for the replies....sorry but I now have one more question...

            So the aircraft with Modes-S that I am receiving, do not plot on my Dump1090-FA map, obviously because they dont have a GPS position.... But yet I can see those aircraft positions being plotted on the Flightradar24 map... how does FR24 know the position?


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            • #7
              Originally posted by kiwiandy View Post
              OK thanks very much for the replies....sorry but I now have one more question...

              So the aircraft with Modes-S that I am receiving, do not plot on my Dump1090-FA map, obviously because they dont have a GPS position.... But yet I can see those aircraft positions being plotted on the Flightradar24 map... how does FR24 know the position?

              The other column listed in yours. MLAT

              https://www.flightradar24.com/how-it-works
              Posts not to be taken as official support representation - Just a helpful uploader who tinkers

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              • #8
                Perfect.. thanks very much

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                • #9
                  Sorry, but one more question.....)
                  How does DUMP1090-fa know what the size aircraft is and what image size to use?
                  2019-12-11 13_53_18-PiAware Skyview - 7_10 - Brave.png2019-12-11 13_53_18-PiAware Skyview - 7_10 - Brave.png

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                  • #10
                    The same way fr24 does (in how it works)

                    None of that info is from planes. (Incl registration)

                    It looks up online databases. Where you can hold a database with the details and match it with hex code.
                    Posts not to be taken as official support representation - Just a helpful uploader who tinkers

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                    • #11
                      Yeah that makes sense! thanks again

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