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  • Linux 53nm and Pi zero 30nm and no lat/long - why?

    I migrated from Windows and have fr24feed installed on a Pi Zero and on Linux Mint (debian) on the previously Windows laptop. Both dump1090-mutability. The Pi zero has adequate power (2.2A). I was very careful to ensure the position of the aerial, RTL dongle, etc remained identical in my testing. Obviously I don't have both running at once as I only have one dongle!

    I have now run both setups for a week each and the Laptop with Mint consistently manages a range of 53nm on the feed-stats (same as Windows did). The Pi zero only 30nm. I should explain that I have hills and mountains around me so that's the extent of my "view". I know where the Windows, now Mint, feed picks up planes at cruising altitudes so I can see what the Pi isn't getting looking at the FR24.com map. I have --gain 48 in the process arguments of both as per Oblivion's "DVBT Feeder Gain Adjustment - WIP" post.

    Looking at the tracked aircraft on the local:8754 page it seems the Pi isn't picking up the lat and long where the laptop is. Just says "N/A". All the other details are there - ModeS, Altitude, Squawk, even Callsign. If it is receiving the lat/long it certainly isn't displaying it. This applies to major commercial aircraft not business jets etc. So presumably the incompleteness of the data is why my range is down on the stats. And even though the gain is set I can't see why it'd be that anyway - if the Pi's gain were too low it wouldn't pick up anything surely?

    I'm flummoxed! Any ideas please?
    Last edited by aka_pseudonym; 2019-05-06, 19:50. Reason: add info

  • #2
    It seems the pi zero doesn't always transfer enough voltage/power to the dongle even with adequate power supply.

    You can try connecting the dongle via a powered USB hub and see if that fixes it.

    Why don't you check http://local/dump1090/ for airplanes? Much better than the :8754 listing.

    Apart from that i would probably recommend a gain of -10 unless you have a flightaware pro stick (plus) or running an LNA.
    Without amplification you don't need to reduce the gain from absolute maximum normally (-10 is about a setting of 55, the next lower setting available is 49.6)

    Comment


    • #3
      Originally posted by wiedehopf View Post
      It seems the pi zero doesn't always transfer enough voltage/power to the dongle even with adequate power supply.

      You can try connecting the dongle via a powered USB hub and see if that fixes it.

      Why don't you check http://local/dump1090/ for airplanes? Much better than the :8754 listing.

      Apart from that i would probably recommend a gain of -10 unless you have a flightaware pro stick (plus) or running an LNA.
      Without amplification you don't need to reduce the gain from absolute maximum normally (-10 is about a setting of 55, the next lower setting available is 49.6)

      Thanks for replying wiedehopf

      I had already tried a powered hub to no avail. Surely with ADSB an aircraft transmits a burst of data and in that burst is all the information? It wouldn't transmit its position separately surely. So if the rest of the data is picked up why not the lat/long? Or more likely why isn't the Pi decoding it.

      Here's an aircraft that flew where I know I can pick them up a few minutes ago. Makes no difference if it's :8754 or /dump1090/ - there's no position being decoded it seems.

      fr1090.png fr8754.png

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      • #4
        You need 2 successive position messages to decode a position.

        So yes bad reception can cause no positions being received.

        Are you sure you are using the same gain for both tests?

        Could also be that the power supply of the pizero or the hub as well is producing electrical noise that reduces reception.

        Especially true when the antenna is close to RPi.

        Comment


        • #5
          Originally posted by aka_pseudonym View Post
          Thanks for replying wiedehopf

          Surely with ADSB an aircraft transmits a burst of data and in that burst is all the information? It wouldn't transmit its position separately surely.

          [ATTACH=CONFIG]10562[/ATTACH] [ATTACH=CONFIG]10563[/ATTACH]
          Location is the last part of the airborne message. There are 4 or 5 types. And when they overlap and can't be processed some are missed if your signal or processing is not up to it.
          Also note the age. That was 5s (or 5ms) ago in the dump1090 window. As in, it hangs onto aircraft incase signal dips and comes back. You might see something still there that has patchy data or not good enough for FR24 to acknowledge presence of as part of the capture/analysis.

          https://www.icao.int/APAC/Meetings/2...B%20Basics.pdf pg 27
          Posts not to be taken as official support representation - Just a helpful uploader who tinkers

          Comment


          • #6
            Thanks widehopf and Oblivion.

            I didn't realise: "You need 2 successive position messages to decode a position." That would explain why the range is less on my FR24 stats page.

            But in Oblivion's Aussie Aviation pdf it says "1090Mhz reply messages (pulse position modulated with error detection)" and on page 27 it says the 56bit message "Airborne position" includes Altitude and Lat Long.

            So presuming the ADSB message has passed the error detection - which it must have or the altitude wouldn't be displayed by the Pi - why is the Lat Long still blank? The Pi must have received the full 56 bits. Does dump1090 need 2 successive positions as well before it'll decode a Lat/Long? It which case it seems a bit daft because surely that information is contained in the last 34 bits of the message!

            I don't think it's a hardware issue - the Pi and power supply are further from the aerial than the laptop - although that'd be better shielded of course. And the Pi isn't taking any more than 350mA of the 2.2A the power supply can offer even without the hub. Just seems as if the Pi fr24feed software is lacking something that's in the debian version on Linux Mint. I'll try setting the gain back to -10 but isn't that the default, where it would have been before I set it to 48? Not a lot flying near me now so I'll have to wait until tomorrow to see if it helps - always presuming the military aren't using the area for training of course in which case everything commercial gives it wide berth of at least 50nm
            .

            Comment


            • #7
              If you think it's the dump1090 verson just try a stretch lite sd-card and install dump1090-fa or dump1090-mutability 1.15.
              (or a piaware sd-card)

              You definitely need 2 position messages within a certain time to decode the position, at least for the first position you decode.
              (https://mode-s.org/decode/adsb/airborne-position.html)

              Maybe you set a lower range and a location in one of the dump1090 installations?
              That would help in only requiring one message to get a position.

              Anyway your reception is really bad it seems.
              Assuming you are using a whip atenna, check this thread:

              https://forum.flightradar24.com/thre...h-DVB-T-Dongle

              But to be honest i would just recommend building a quick spider or something along those lines.
              Or get this antenna from ebay along with a male to male SMA adapter:
              https://www.ebay.de/itm/1pcs-ADS-B-P...E/253915016420

              It's about the same or a little better than a homebuilt spider.

              Comment


              • #8
                May be the USB cable between Dongle & Pi Zero is no good. Try another one.

                TomMuc's Pi Zero W
                TomMuc - Pi Zero W.jpg

                Comment


                • #9
                  Originally posted by wiedehopf View Post
                  ....Or get this antenna from ebay along with a male to male SMA adapter:
                  https://www.ebay.de/itm/1pcs-ADS-B-P...E/253915016420

                  It's about the same or a little better than a homebuilt spider.
                  This is electrically same as "die koaxielantenne" with following physical differences

                  1. It is stripline flat, instead of solid 3-D
                  2. The internal feed line is a twin-lead parallel-wire transmission line instead of a coaxial cable.
                  3. The whip has been broadened by making it a fork instead of single wire.


                  strioline ant 1.jpg . stripline ant 2.jpg stripline ant 3.jpg


                  (Translation in English in red color by me)
                  Last edited by abcd567; 2019-05-07, 07:01.

                  Comment


                  • #10
                    Originally posted by wiedehopf View Post
                    Anyway your reception is really bad it seems.
                    Originally posted by abcd567 View Post
                    May be the USB cable between Dongle & Pi Zero is no good. Try another one.
                    Thanks for all the advice. I know my reception is bad - I'm in a dingle with mountains all around me. A 1,000m pole for the aerial would be the only cure! I only started tracking about five or six years ago to pick up the military. Now I do it to keep the FR24 business subscription. But I don't like things that aren't working properly - it annoys me!

                    Anyway I tried to think laterally and the only difference between the Linux laptop feed and the Pi Zero feed is that MLAT is OFF on the Linux and is ON on the Pi

                    With the PI :8754 shows it "ON. And -status shows MLAT as OK:


                    Untitled2.png


                    But what's this "[mlat][i]No ADS-B time reference available (0/0)" in the log?


                    Untitled1.png


                    I'm sure that must be it but I don't understand why. Not many planes today as the military are playing about (all with transponders off) but my feed stats currently show Aircraft 29, Positions 46, Hits 364, Distance 0nm. Any ideas please?
                    Last edited by aka_pseudonym; 2019-05-07, 13:53. Reason: duplicate, no pics

                    Comment


                    • #11
                      The mountains are not the reason for getting bad reception when the aircraft is in direct field of view.

                      Most likely your antenna/dongle setup is just bad.

                      Comment


                      • #12
                        Originally posted by wiedehopf View Post
                        The mountains are not the reason for getting bad reception when the aircraft is in direct field of view.

                        Most likely your antenna/dongle setup is just bad.
                        Same setup on Linux and Pi so you'd expect the antenna/dongle to be bad on both. I've tried alternative leads as abcd567 suggested.

                        Not sure this pic appeared correctly on my previous post. I'll add it again. Do you know what "[mlat][i]No ADS-B time reference available (0/0)" refers to?


                        Untitled1.png

                        Comment


                        • #13
                          Yeah you might just not believe me, but your reception is bad. Try and improve your antenna.

                          Due to the power being supplied to the dongle being worse on the RPi the reception might be a bit worse making it insufficient.
                          It's hard to tell when the starting point is basically no reception.

                          No time reference available just means that you aren't receiving any aircraft. It's a time reference to a message sent by an aircraft.
                          If you don't receive any aircraft then there will be no reference messages.

                          Comment


                          • #14
                            Originally posted by wiedehopf View Post
                            Yeah you might just not believe me, but your reception is bad. Try and improve your antenna.

                            Due to the power being supplied to the dongle being worse on the RPi the reception might be a bit worse making it insufficient.
                            It's hard to tell when the starting point is basically no reception.

                            No time reference available just means that you aren't receiving any aircraft. It's a time reference to a message sent by an aircraft.
                            If you don't receive any aircraft then there will be no reference messages.
                            Thanks for that information.

                            I do believe you! And I think "... power being supplied to the dongle being worse on the RPi the reception might be a bit worse making it insufficient." is right.

                            I've turned off MLAT on the Pi now so I'll see how it manages over a few days.

                            To get my "full" range needs something over 40,000ft to fly by 50nm away in a NNE direction. Usually a business jet as their flight plans seem to be 40,000ft plus. So it doesn't happen instantly. Here's my elevation - 360 degree plot. And it doesn't show trees and forests in the way so it's really even more closed in. Pretty ridiculous place to be tracking planes really.


                            profile.jpg

                            Comment


                            • #15
                              If you have a small whip antenna, consider modifying your antenna like described in this thread:

                              https://forum.flightradar24.com/thre...h-DVB-T-Dongle

                              Also i'm pretty sure using -10 as a gain will provide better results unless you have Flightaware Pro Stick.

                              Quite aware that the range isn't gonna be good with your terrain, that i believe.
                              But once the aircraft are "in view" you should get plenty of messages and a solid track.

                              (Where is the antenna located? Pretty much no matter what improving the antenna like described in the thread can improve things a lot)

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