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Very Dim Newbie v What Am I Seeing

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  • #46
    In my opinion the filter will likely reduce range in your case.
    The noise isn't overly strong and no one can say for certain if it's overloading anything.

    (Overload problems are more likely with the Flightaware Pro Stick Plus because it has a builtin LNA that is sensitive to overloading.)

    Just get the rtl-sdr LNA and be done with it. It shouldn't be much more expensive and especially if you just have a standard dongle right now, the improvement will be much bigger than just buying one of those filters.
    The problem with the filters mentioned is that they reduce the signal as well.

    It's a little more tinkering involved to get either a bias-t and supply 5V that way.
    Or you get their rtl-sdr blog v3 dongle as well and then you do some fiddling in the software to activate the internal bias-t. (guides available)

    Edit: Ok, just properly read the thread and saw that you are using the ProStick Plus.
    I'll still recommend the LNA, the performance per dollar you gain is just much better in my opinion.
    (Not sure how much the filter is in Australia though)

    Also -10 is the highest gain setting. It's called automatic gain control, but that was designed for DVB-T signals, the original purpose of the rtl-sdr chipsets.
    ADS-B is too intermittent a signal, so AGC does not work and just switches the gain to maximum.
    Last edited by wiedehopf; 2019-06-11, 07:36.


    • #47
      Glad you spotted I am using the ProStick Plus

      I will get the LNA as you suggest, because that is another gadget as well. I'm like a jackdaw and like collecting shiny things

      A gain of -10 is the highest setting. This is what I don't understand; why is a negative setting higher than a positive setting?

      I've had the gain set at -10 for about 7:45 now. The messages > -3dBFS is 11.6%. Max range in the last 6 hours has been 217.5nm (220nm within 24 hours i.e. when gain was not adjusted). The ADSB signal level looks like the attached graph. Going by what you said before I think I may have to turn the gain down a bit. Does this mean I now have to put --gain 49.6 or would your advice to be to get rid of the --gain instruction altogether?

      Sorry to keep asking silly questions. I have tried to Google the whole gain thing but I'm still puzzled why a -ve number gives a higher gain
      Attached Files


      • #48
        Because its DBFS

        '0' on the scale is maximum. -50 the other end

        -10 is just the trigger to make the app go 'auto gain' while other values are valid fixed gain levels on the scale.

        As '-' is a command trigger for most things linux, the values need to be entered in + increments.

        Per abcd
        The dongle gain can only be set to a value between 0 and 49.6
        The dongle does NOT accept any negative (-) value of gain.
        The gain value -10 is a special number. It does NOT sets gain to -10 . It SWITCHES dongle into AGC mode (Automatic Gain Control mode). In this mode the dongl dynamically adjusts gain according to received signal strength.
        Posts not to be taken as official support representation - Just a helpful uploader who tinkers


        • #49
          --gain 49.6 is the default setting with dump1090-mutability.
          So you could remove it altogether but i would have it in there explicitly, then you don't need to look up default values.

          The negative number is just a programming thing.
          It's not a normal gain value, in other words a special value.

          Special values are often represented by negative numbers if those are not in the range of values.

          So it's just a label, not a number.

          So in the logic of the driver it checks first if the gain is set to -10 and accordingly enables AGC for you.
          Otherwise it will set the gain you entered.

          Hope that makes some sense.

          And due to AGC being made for other signals than ADS-B, the automatic is dumb and just sets to the maximum possible.
          This maximum possible is due to bad driver programming not available as a discrete value (technically it is possible).

          If you use the LNA, you don't need the filter. In fact using the dark blue filter in front of the LNA would reduce LNA performance.
          But if you like trinkets anyway, go right ahead.

          In that case i'd just order the rtl-sdr v3 stick and use that with the rtl-sdr LNA. (
          Then you can have a second station with the Flightaware Pro Stick Plus and the dark blue filter.

          Or you can test which combination you like better


          • #50
            Thanks guys. Now the -10 makes sense. No wonder I couldn't figure it out when trying to increase gain!! However, nothing is wasted and I now know more than I did this morning about isotropic things, gain and (sort of) DBFS


            • #51
              (1) Dump1090-mutability: About gain -10

              (2) ABOUT AGC


              • #52
                I think I should use the search function for the forum more and Google less. Thank you, abcd567


                • #53
                  Well, the search funtion in FR24 forum is not very good. I have to use [my memory+ forum search].

                  Another read of interest is linked below. It is an "aid to gain setting". As you have already installed graphs, this is not of much practical use for you, but definitely very useful for those who dont have graphs.

                  How-to Add "Received Signal Strength Indicator" (RSSI) Column in Aircraft Table of dump1090-mutability ver 1.15~dev



                  • #54
                    You can use Google to search a specific site and it works very well. I forget the syntax at the moment, you'll have to Google it :-)


                    • #55

                      Unfortunately if you put in .vn Viet or escorts you get to see all the dodgy urls SEO spammers add to their profiles.
                      Last edited by Oblivian; 2019-06-11, 23:58.
                      Posts not to be taken as official support representation - Just a helpful uploader who tinkers


                      • #56
                        Originally posted by Oblivian View Post

                        Unfortunately if you put in .vn Viet or escorts you get to see all the dodgy urls SEO spammers add to their profiles.
                        I just knew that there were at least a couple of people that couldn't resist posting :-)


                        • #57
                          Forum has a minimum 4 char requirement. And - between reg is unfortunately 'ignore' which makes it hard.

                          Sent from my EML-L09 using Tapatalk
                          Posts not to be taken as official support representation - Just a helpful uploader who tinkers


                          • #58
                            For Google search of key words in the FR24 forum, you have to enclose search keywords in quotes like this:

                   "about agc"

                   "rssi column"


                            • #59
                              Lots more good stuff

                              I've added the rssi column to my Dump1090 map and that seems to work very well, so thank you for that. Previoulsy I only got the rssi information on the target I clicked on.

                              I do like the look of the embedded gain button (it's another gadgety thing) and I'm getting quite good at monkey see, monkey do (I even managed to save the changes to the files even though not specifically instructed to. That's not a criticism because to most it would be obvious but I did wonder if it was all done magically at the end but decided it wasn't and used the steps in the other 'how to' guides I've used to save everything).

                              Anyway, the only question I have at the moment is how to discover if I have Jessie or Stretch. I'm 99.9% certain I have Stretch, as my Pi is very new and I only loaded Raspbian etc a few days ago but I just wondered if there is a way I can check.

                              Edited to add: sorry, ignore that. Google to the rescue again


                              • #60
                                To find which distro (jessie or stretch or something else) you have:

                                cat /etc/os-release