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Thread: Interference on 1090 MHz

  1. #1
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    Interference on 1090 MHz

    Hello

    I contacted FR24 several times regarding interference on the 1090 MHz band where F-SBFI2 feed is located. I also host FlightAware receiver, which has lost range too. The range decreased from approx 200 nm down to 33-39 nm. Coverage is very poor.

    I had checked using FlightAware ProStick + FlightAware BPF the 1090 MHz band using SDR# (the only tools I have now) and I found a disturbing lump close to 1088 MHz. If the RTL AGC is left on the noise floor skyrockets a very high and disturbing level. I have attached screenshots of SDR# below:

    RTL AGC ON
    RTL AGC ON - TUNER AGC ON.jpg

    RTL AGC OFF
    RTL AGC OFF - TUNER AGC ON.jpg

    I am trying to reach FR24 support but get no reply from them. I managed to get range back using the FA ProStick + BPF as above running with RTL AGC OFF and TUNER AGC ON which gave range back, as below:

    6916341b-70de-4158-8c0f-f069c7dafbf6.jpg

    Is there any way gain could be turned down on a FR24 receiver ? Seems that too high a gain is pumping noise up too much.

    There are no cell towers or anything new in the vicinity. This receiver has been installed on this site for almost two years with no issues.

    Any insights will be much appreciated.

    Ricardo
    F-SBFI2
    Brazil

    EDIT: After posting I realized I posted on the wrong forum. Cannot delete or move post. Sorry for any inconvenience.
    Last edited by ricardogerassi; 2019-03-26 at 23:43.

  2. #2
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    Dump1090 has --gain options

    Depending on if you have separate service running or allowing FR24feed to start it

    https://forum.flightradar24.com/thre...highlight=gain
    Posts not to be taken as official support representation - Just a helpful uploader who tinkers

  3. #3
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    High noise floor is normal with the builtin LNA, not quite as high though i guess.

    The lump is interesting though.

    Being almost exactly 1090 MHz i would suspect one of your receivers to be faulty.
    As i suggested on the flightaware forum already you should test the receivers separately.

    If one regains full range when the other one is powered off, the powered off one is the faulty one.

    Or you could check the noise using SDR# and switch the other receivers on and off and check if something changes.
    If you have a mobile antenna you could also "search" for the noise.
    Last edited by wiedehopf; 2019-03-27 at 00:24.

  4. #4
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    Quote Originally Posted by wiedehopf View Post
    High noise floor is normal with the builtin LNA, not quite as high though i guess.

    The lump is interesting though.

    Being almost exactly 1090 MHz i would suspect one of your receivers to be faulty.
    As i suggested on the flightaware forum already you should test the receivers separately.

    If one regains full range when the other one is powered off, the powered off one is the faulty one.

    Or you could check the noise using SDR# and switch the other receivers on and off and check if something changes.
    If you have a mobile antenna you could also "search" for the noise.
    I did several tests. Shut down one of the receivers and check if the remaining one recovers range; turned off the UPS powering the receiver directly from the outlet; measured the AC adapter AC level on the DC output for noise; turned off the ethernet switch; turned off LiveATC RPi that is on the same rack; I did that for each receiver and had no success whatsoever.

    After posting I went further up on the spectrum using SDR# and was able to demodulate a beating between two FM stations but that was close to 1108 MHz.

    I am considering powering off my entire home main AC breaker and run the FA ProStick + BPF on the notebook's battery. I truly believe that there is a strong interference outside home but I gotta rule out any possibility.

    Interesting enough this FA antenna I am using is brand new. Connectors are like new and the antenna has no sign of moisture contamination.

    What is really driving me nuts is that the FR24 Box Receiver is not getting rid of the interference, like having a stuck gain and I cannot do anything about it because FR24 staff has the ability to change something in it. What I do know is that using a FA ProStick + BPF + RTL1090 on a windows pc I was able to restore the 200 nm converage I had before.

    Hope FR24 guys fix F-SBFI2 receiver ASAP. I am even considering adding another T- receiver in here to provide coverage.

  5. #5
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    The antenna connected to the dongle shown in SDR#, was that one of the installed antennas or did you use a portable one?

    With a portable antenna you can check how the signal changes when you point the antenna in different directions.

    Basically if you point the antenna at something with the tip and the noise is gone, that is the direction where the noise is coming from, or it is the exact opposite direction.
    The antennas are made to best receive on the horizon, directly above and below reception is bad.

  6. #6
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    Quote Originally Posted by wiedehopf View Post
    The antenna connected to the dongle shown in SDR#, was that one of the installed antennas or did you use a portable one?

    With a portable antenna you can check how the signal changes when you point the antenna in different directions.

    Basically if you point the antenna at something with the tip and the noise is gone, that is the direction where the noise is coming from, or it is the exact opposite direction.
    The antennas are made to best receive on the horizon, directly above and below reception is bad.
    I have used the rooftop antenna. Did not use the portable and will give it a try. Anyway I will build a RPi + FA ProStick + BPF to act as a backup while this issue is now solved.

  7. #7
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    You should have an extra flightaware antenna now that they sent you a new one

    Optimal usage: looking for noise

  8. #8
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    Quote Originally Posted by ricardogerassi View Post

    Interesting enough this FA antenna I am using is brand new. Connectors are like new and the antenna has no sign of moisture contamination.
    The new dark green antenna they sent me went bad after about 2 months up on my tower on a beautiful sunny day. Range just suddenly dropped off. I switched to another ADS-B antenna and all was good. I never got around to cutting it open to see what was inside that could have caused the issue, that would be interesting to know.

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