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Thread: Non ADS-B. Mode S only aircraft

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    Non ADS-B. Mode S only aircraft

    My own radar is picking up plenty of Mode S only traffic, and sometime these are displayed on the fr24 map originating from an MLAT source which i understand.
    What i don't understand is sometimes this Mode S traffic shows as originating from a T-xxxxxx feeder, which i had assumed is using the same technology as Rpi implementation.

    Can someone be kind enough and explain therefore how t-xxxxxx feeder can show as obtaining a location fix on an aircraft that is only transmitting Mode S ? Is this an Fr24 anomaly or are they getting the GPS co-ordinates from another source ?

    Thanks

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    Quote Originally Posted by awitty View Post
    My own radar is picking up plenty of Mode S only traffic, and sometime these are displayed on the fr24 map originating from an MLAT source which i understand.
    What i don't understand is sometimes this Mode S traffic shows as originating from a T-xxxxxx feeder, which i had assumed is using the same technology as Rpi implementation.

    Can someone be kind enough and explain therefore how t-xxxxxx feeder can show as obtaining a location fix on an aircraft that is only transmitting Mode S ? Is this an Fr24 anomaly or are they getting the GPS co-ordinates from another source ?

    Thanks
    A T-xxxx feeder can be anything other than an official FR24 box, it may well be someone with a radarcape which is basically the same as an official box but privately purchased and running different firmware, these are capable of MLAT but will still be shown as a T-xxxx
    FR24 F-EGLF1, Blitzortung station 878, OGN Aldersht2, PilotAware PWAldersht, PlanePlotter M7.

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    Quote Originally Posted by F-EGLF1 View Post
    these are capable of MLAT but will still be shown as a T-xxxx
    Thanks, but i don't quite follow your last statement. I had assumed that FR24 servers handled all the multilateration algorithm calculations (and not feeder boxes), and thus displayed the Radar as MLAT when the position was derived from the associated timing data from 3 or more feeders.

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    For example Mode S traffic shows as originating from a T-xxxxxx feeder then feeder have 4+ Raspberry Pi receivers with properly working MLAT calculating server backing location data to this receivers.

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    Quote Originally Posted by DrHyperKALICH View Post
    For example Mode S traffic shows as originating from a T-xxxxxx feeder then feeder have 4+ Raspberry Pi receivers with properly working MLAT calculating server backing location data to this receivers.
    Ok I understand. So it's not uncommon then for someone to have a multi receiver setup and undertake their own Mlat calculations before feeding this data up to fr24.

    Thanks for the help.

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    It's more they are likely sending fr24 data flagged as positional, when it's been pre processed but not really (ala mlated somewhere)

    Sent from my XT1092 using Tapatalk
    Posts not to be taken as official support representation - Just a helpful uploader who tinkers

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    Quote Originally Posted by Oblivian View Post
    It's more they are likely sending fr24 data flagged as positional, when it's been pre processed but not really (ala mlated somewhere)

    Sent from my XT1092 using Tapatalk
    I just did a search for one of the offending radars and found this thread;
    http://forum.flightradar24.com/threa...erry-Pi/page36

    It is suggested that some FR24 feeds are feeding positional data from piaware.

    Thanks for all your help. I understand what's going on now.

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    I'm still confused. How would having multiple receivers at the same location make any difference on establishing position?

    I just started feeding to FR from close to KSJC about a week ago and have yet to see my feed in any of the radar boxes.
    There are only 5 or 6 T-XXXX radars that are shown as the source for 95% of the aircraft within 50 miles of the Bay Area and they always have position info when I often have only a ICAO, altitude and speed.

    I've also seen aircraft (PAL airline flight) that I was feeding with full position information and was not showing on FR24 until it was within 30 miles of KSJC.
    Using RPi2 and dump1090. T-KSJC28

    Also, there is no doubt there are at least 20 feeders in the bay area and you rarely see the "MLAT-" radar as the source. I fed my antennas lat and long coordinates to FR24 with 6 digits of accuracy in hopes it would improve the accuracy of flights in the area via MLAT.
    Last edited by Sam26K; 2016-01-23 at 07:30.

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    Quote Originally Posted by Sam26K View Post
    I'm still confused. How would having multiple receivers at the same location make any difference on establishing position?

    I just started feeding to FR from close to KSJC about a week ago and have yet to see my feed in any of the radar boxes.
    There are only 5 or 6 T-XXXX radars that are shown as the source for all the aircraft within 100 miles of the Bay Area and they always have position info when I only receive a ICAO and a few other parameters.

    I've also seen aircraft (PAL airline flight) that I was feeding with full position information and was not showing on FR24 until it was within 30 miles of KSJC.
    Using RPi2 and dump1090. T-KSJC28

    Also, there is no doubt there are at least 20 feeders in the bay area and you rarely see the "MLAT-" radar as the source. I fed my antennas lat and long coordinates to FR24 with 6 digits of accuracy in hopes it would improve the accuracy of flights in the area via MLAT.
    It comes from this:

    Some FR24-feeders are also feeding other networks. One of these networks are calculating a position for S-mode aircraft using MLAT (just like FR24) BUT ALSO have the added feature of sending the MLAT position back to the feeder for local display. Some of these feeders then retransmit the MLAT position to FR24 as if it was an ADS-B position received directly form the aircraft and FR24 will then mark it with that feeder name.
    FR24 are aware of this but have not been able to filter out these 'stolen' positions. This have been going on for a year or so.

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    Quote Originally Posted by Kpin View Post
    It comes from this:

    Some FR24-feeders are also feeding other networks. One of these networks are calculating a position for S-mode aircraft using MLAT (just like FR24) BUT ALSO have the added feature of sending the MLAT position back to the feeder for local display. Some of these feeders then retransmit the MLAT position to FR24 as if it was an ADS-B position received directly form the aircraft and FR24 will then mark it with that feeder name.
    FR24 are aware of this but have not been able to filter out these 'stolen' positions. This have been going on for a year or so.
    Thanks for explaining that, Kpin. That makes perfect sense why they appear from a T-Feeder instead of an MLAT feeder. I kept thinking that it was a superior receiver or an FR24 fluke in the source reporting.

    If the data is good, there is no problem with that, but often it's not good when the aircraft are taking off and landing and taking the tight turns they do around KSJC. I was hoping to contribute to improving that situation but so far FR24 does not seem to be tracking my feeder even though it's uploading.

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