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Thread: MLAT is now live on Flightradar24

  1. #431
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    It would be interesting to see which receivers are tracking an A/C for an MLAT plot.
    Indeed it would, but I think it would eat up too much bandwidth.
    F-KDAG1

  2. #432
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    Quote Originally Posted by FlyoverCountry View Post

    I still wonder why other receivers are listed as tracking a plane when it is so close to me. Perhaps the other receivers have a better signal strength even when farther. It would be interesting to see which receivers are tracking an A/C for an MLAT plot.
    (and for Real-Duke)

    Firstly a word to the Moderators, if you think this response is in the wrong place or would be better served elsewhere, by all means place it where it could be better served.

    As to your question guys, you're not the first to ask this question and most likely won't be the last. There seems to be many confused as to why an aircraft flying directly over your receiver is rarely seen on the map (if ever) and most likely placed there by a receiver 100 or more nautical miles from your location. It has nothing to do with FR24 or their server/s (although the server's software does determine in the main which receiver will 'paint' an aircraft on the FR24 map and is discussed elsewhere on the forum).

    Please refer to the attachment below which is a screenshot taken from my laptop some 10 months or so ago.

    If you look at the track of the climbing BAW16 and the similar (earlier) track of a climbing A380 (I think it was SIA222) nearby you can see that once within about 12nm overhead my receiver (the circle in the centre of the range rings) that the signal from the aircraft begins to break up. The aircraft are climbing from right to left out of YSSY (Sydney, Australia). Unfortunately those who don't have an SBS-1 or similar as I have which displays a simulated 'radar' screen on the laptop/pc which is very similar to what an Air Traffic Controller would see may not have the ability to appreciate what is happening. The aircraft is punching out a signal roughly once every second or close to it, but the closer to overhead the antenna, the more signals we miss (if we have a vertically polarised antenna). VOZ1628 on descent outside the 12nm range has a very clean path towards the airport and so you can see my antenna is picking it up unobstructed. The other track alongside VOZ is simply a general aviation aircraft having a bumpy ride on climb out since its track colour changes rapidly and repeatedly. Even that track is affected in places. If watching it on your own software it can be barely noticeable and so easily missed, but can make a massive difference when it comes to whether your radar will appear on the map 'holding' a particular aircraft.

    So it's all to do with the antenna reception, which you can find a whole lot more technical information about if you read ABCD567's posts in 'best antenna' and his other very well written threads on the forum.

    If you think of a TV antenna, it is horizontally polarised, meaning that it points directly at a transmitter or a repeating station (hopefully) and so picks up signals parallel with the ground. Many of our ADS-B antenna's (if not most) are sticking up straight in the air (vertical) and so when aircraft track directly overhead we begin to lose the pulses transmitted by the aircraft and as you can see, can last quite a few seconds in places. A receiver many miles away doesn't have that limitation and so is more likely to display the aircraft flying over you. It's purely because the signal from the aircraft is getting outside the reception range of our antenna (it's flying over the pointy top of the antenna or close to it). Those gaps give other radars every opportunity to chime in on 'your' aircraft close to overhead your location as FR24 are looking for uninterupted signals to paint on the map. This is a fairly basic explanation but I hope it's relatively easy to understand and more importantly, can see it's just the nature of our setup.

    I also have a discone antenna which I used to use but it's a wide band antenna and not much use for ADS-B 1090MHz and is mounted much lower so range is limited a bit and I can't say that I've compared them in terms of missed overhead reception.

    There's also another anomoly worth mentioning here which becomes apparent near an airport (landing or departing aircraft but usually more noticeable on landing) and that is to do with multiple 'radars' displaying an aircraft through a turn, often in rapid succession on the FR24 map. An aircraft may get vectored onto a downwind leg, thence base leg, thence to approx. 30 degrees to the ILS before intercepting it and landing. It may go through a number of turns during this procedure and when doing so the 'radar' station on the map can flip from one receiver to another and even more than 2 receivers. Nothing to do with FR24 again, simply a matter of radar location and the fact that there are two ADS-B antennas on an aircraft (most jets and larger turbo's), one above and one below the fuselage roughly in line with the rear of the avionics bay. It doesn't take much to block these at low altitudes as they aren't all that large (in comparison to the VOR or ILS antennas) and even the engine or parts of the fuselage itself, the wing/s or wing tip fences or the tail fin or rudder can also do so. Not to mention the landing gear as well at certain times. It can be all a matter of luck.

    So any conspiracy theorists out there (not you 2 guys) thinking that FR24 is up to something in these situations, I can say with certainty that they aren't.

    MAP4.jpg

    Regards,
    Gregg
    Last edited by fungus; 2016-05-01 at 03:37.
    YSSY2/T-YSSY4 [SBS-1 Basestation w/- SSE-1090 SJ Mk2 Antenna (Thanks Delcomp) ] [Uniden UBCD996T w/- 16 element Wideband Discone VHF/UHF Antenna, and tuned 108MHz-137MHz Airband Antenna] [Trialing a home-brew 1090MHz collinear antenna]

  3. #433
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    The problem with most feeders that are identified on FR24 as ADS-B fully defined radar sources; and then the A/C shows up on local receivers as mode-s only are leaking MLAT data from other sources.
    It's not that complicated and it's obvious.

    Edit: I should clarify this comment. It does require a minimum signal strength for your specific receiver to acquire the full ADS-B position data. If you see the same feeder feeding A/C's with full ADS-B data that you know you have a solid lock on with your receiver, and you don't have the full ADS-B tag, you know they are MLAT leakers.
    Last edited by Sam26K; 2016-04-30 at 08:36.

  4. #434
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    Quote Originally Posted by Sam26K View Post
    The problem with most feeders that are identified on FR24 as ADS-B fully defined radar sources; and then the A/C shows up on local receivers as mode-s only are leaking MLAT data from other sources.
    It's not that complicated and it's obvious.

    Edit: I should clarify this comment. If you see the same feeder feeding A/C's that you know you have a solid lock on with your receiver, you know they are MLAT leakers.
    It does require a minimum signal strength for your specific receiver to acquire the full ADS-B position data.
    Completely unrelated, and not a necessary post
    Posts not to be taken as official support representation - Just a helpful uploader who tinkers

  5. #435
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    Quote Originally Posted by Oblivian View Post
    Completely unrelated, and not a necessary post
    I was replying to an earlier post ..
    "Quote Originally Posted by FlyoverCountry View Post
    I still wonder why other receivers are listed as tracking a plane when it is so close to me.
    Same here even if the plane flys directly over my house it shows another feeder but afaik its normal."

    I thought that was related. BTW, I hope you're not still defending MLAT leakers. I have followed up with the problem with FR24 and they agree with me so far.

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