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  • Do I need a Filter? - Find RF Signals In Area

    The space around ADS-B antenna contain not only 1090 MHz signals, but also lot of other signals at different frequencies. The closer the frequency of a signal to 1090 MHz, your ADS-B antenna picks it stronger. For example if there are three signals of equal strength, one at 144 MHz, 2nd at 850 MHz and 3rd at 950 MHz, the ADS-B antenna will pick 950 MHz one the strongest, 850 MHz one a bit less stronger, and 144 MHz one much fainter.

    As the Cell/Mobile/Pager signals exist in the range 850 MHz to 1200 MHz, these are picked strongly by ADS-B antenna and this mixture is fed to the receiver, overloading its front end tuner. To overcome this situation, a hardware called “Filter” is used. As its name shows, it filters out unwanted signals and passes a narrow band of frequency say 1075 MHz to 1150 MHz, blocking most Cell/Mobile/Pager signals from reaching the receiver.


    Mobile / Cell Phone Frequencies Close to 1090 MHz ES and 978 MHz UAT

    BAND NAME REGIONAL DEPLOYMENT CENTER FREQUENCY OF THE BAND UPLINK
    (mobile to tower)
    DOWNLINK
    (tower to mobile)
    GSM-850 GSM-850 is used in most of North, South and Central America
    (ITU-Region 2).
    Also in Australia & New Zealand
    850 MHz 824 – 849 MHz 869 – 894 MHz
    GSM-900 / EGSM-900 GSM-900 is used in most parts of the world: Africa, Europe, Middle East, Asia (apart from Japan and South Korea where GSM has never been introduced) and Oceania.
    (ITU-Regions 1 and 3)
    900 MHz 880 – 915 MHz 925 – 960 MHz

    In order to determine if a filter is needed or not, it is necessary to scan frequencies in the range 800 MHz to 1200 MHz. If the scan shows very few and weak interfering signals, adding a filter will not give any appreciable improvement. On the other hand if the scan shows a lot of strong interfering frequencies, adding a filter will give substantial improvement in ADS-B 1090 MHz reception.

    Software developers have developed softwares which use (DVB-T+ADS-B Antenna) to perform this scan. There are following two ways it can be done. Please click the options below to see the details.


    OPTION-1:
    DVB-T is plugged into Raspberry Pi (or is plugged into a Desktop/Laptop running Linux Debian/Ubuntu)

    OPTION-2:
    DVB-T is plugged into a Windows Computer - Using GUI rtlpan.exe.

    OPTION-3:
    DVB-T is plugged into a Windows Computer - Using Command Line.

    Last edited by abcd567; 2019-06-11, 05:48.

  • #2
    OPTION-1:
    DVB-T plugged into Raspberry Pi.

    This method uses software tool rtl_power which is part of software package rtl-sdr.

    Credits:
    Kyle Keen (keenerd): For rtl_power and heatmap.py
    Oliver Jowett (obj): For guide how to use rtl_power and heatmap.py


    STEP-1 of 6:
    Install required packages (rtl-sdr and python-imaging), and get the python script (heatmap.py) to create image scan.png from scanned data stored in file scan.csv

    Code:
    sudo apt-get install rtl-sdr
    sudo apt-get install python-imaging
    sudo wget https://raw.githubusercontent.com/keenerd/rtl-sdr-misc/master/heatmap/heatmap.py
    sudo chmod +x heatmap.py

    STEP-2 of 6:
    Free the DVB-T Dongle which is in use by a decoder like dump1090, or dump1090-mutability, or dump1090-fa.
    Code:
    sudo systemctl stop dump1090
    sudo systemctl stop dump1090-mutability
    sudo systemctl stop dump1090-fa
    sudo systemctl stop fr24feed
    sudo systemctl stop piaware
    STEP-3 of 6:
    Once DVB-T Dongle has been made free, run following test
    Code:
    sudo rtl_power -f 800M:1200M:100k -i 30 -c 50% -e 30m -g 30 -F 9 >scan.csv

    The above command will generate following output.
    Code:
    Number of frequency hops: 286
    Dongle bandwidth: 2797202Hz
    Downsampling by: 1x
    Cropping by: 50.00%
    Total FFT bins: 9152
    Logged FFT bins: 4576
    FFT bin size: 87412.56Hz
    Buffer size: 16384 bytes (2.93ms)
    Reporting every 30 seconds
    Found 1 device(s):
      0:  Realtek, RTL2832U, SN: 00001003
    
    Using device 0: Generic RTL2832U
    Detached kernel driver
    Found Rafael Micro R820T tuner
    Tuner gain set to 29.70 dB.
    Exact sample rate is: 2797202.148434 Hz
    [R82XX] PLL not locked!

    Wait for 30 minutes for scan to finish.
    When scan is finished, it will say "Exiting.... Canceled by user".
    Scan will create a file "scan.csv" in current folder and save scan data in it.

    This will produce a very wide image (4000 pixels!) that shows spectrum power from 800MHz - 1.2GHz.
    If you want a narrower image, increase “100k” above to something larger, it controls the bandwidth that corresponds to one pixel on the x axis.
    -i controls the integration interval (time for one pixel on the y axis)
    -e is the total runtime, longer gives you a taller image.


    STEP-4 of 6:
    Don't forget to Reboot Pi so that system is restored to normal, and data feeding is restored.
    Code:
    sudo reboot

    STEP-5 of 6:
    Create an image "scan.png" in current folder from data stored in file "scan.csv"
    Code:
    ./heatmap.py scan.csv scan.png
    This will produce a very wide image (4000 pixels!) that shows spectrum power from 800MHz - 1.2GHz.


    STEP-6 of 6:
    Copy the image "scan.png" from Pi to your Win/Mac Computer. To copy a file from Pi, you will need to install on your Win/Mac computer an SCP software. Some popular free of cost software are FileZilla (win and mac) or WinSCP (win) or CyberDuck (win and mac). Another Software which has both SCP and SSH is Bitvise SSH Client (Windows).



    Example of Scan of Existing RF Signals by rtl-power

    The original image is very wide (4000 pixel), but displayed in this forum smaller (874 pixel). As a result details are not clear.




    Three 500 pixel wide cut-outs from above 4000 pixel wide image. These cutouts show details better.





    Last edited by abcd567; 2019-06-10, 12:57.

    Comment


    • #3

      OPTION-2:
      DVB-T plugged into Windows Computer - Using GUI rtlpan.exe


      Important: If you want to plug in your DVB-T Dongle into Windows Computer, you should install its driver Zadig.

      STEP 1 of 7:
      Create a new folder of a name of your choice and at a location of your choice. For this guide, I will use new folder name "RF Scan", location inside "Download" Folder.

      STEP 2 of 7:
      Download RelWithDebInfo.zip from here:
      Download Link: http://osmocom.org/attachments/downl...ithDebInfo.zip

      Web Page: https://osmocom.org/projects/sdr/wiki/rtl-sdr
      (scroll down to bottom of page to find download link)


      STEP 3 of 7:
      Un-zip RelWithDebInfo.zip. It will create a folder RelWithDebInfo and inside this folder another folder rtl-sdr-release which contains several files and 2 folders named x32 and x64 . Copy ALL files of folder x32 into newly created folder RF Scan.

      STEP 4 of 7:
      Download rtlplan.exe from the site given below, and save it inside the folder RF Scan
      https://sourceforge.net/projects/guiforrtlpower/





      STEP 5 of 7:
      Double-click rtlpan.exe to start the software.

      STEP 6 of 7:
      In the rtlpan window, make settings as follows (see screenshot below)
      start freq: 800Mhz (800000000)
      end freq: 1200Mhz (1200000000)
      step: 100kHz
      Gain: 49.6



      STEP 7 of 7:
      Press "START" Button. The scan will start and the scan image will start building gradually. Wait for about 15 to 30 minutes for scan image to build to sufficient height. Click "STOP" button to stop the scan. In addition to scan image, a file scan.csv will be generated inside folder "RF Scan"




      Last edited by abcd567; 2018-04-13, 15:08.

      Comment


      • #4
        OPTION-3:
        DVB-T plugged into Windows Computer - Using Command Line


        Important: If you want to plug in your DVB-T Dongle into Windows Computer, you should install its driver Zadig from http://zadig.akeo.ie/


        STEP 1 of 7:
        Download Python Installation File python-2.7.14.msi from the site given below, and install it on your computer
        https://www.python.org/downloads/

        STEP 2 of 7:
        Download Python Imaging Library Installation File Pillow-4.3.0.win32-py2.7.exe from the site given below, and install it on your computer
        https://pypi.python.org/pypi/Pillow/4.3.0

        IMPORTANT NOTE: Pillow and PIL are not compatible. If you have already installed PIL, first uninstall it, and then install Pillow




        STEP 3 of 7:
        Create a new folder of a name of your choice and at a location of your choice. For this guide, I will use new folder name "RF Scan", location inside "Download" Folder.

        STEP 4 of 7:
        Download RelWithDebInfo.zip from here:
        Download Link: http://osmocom.org/attachments/downl...ithDebInfo.zip

        Web Page: https://osmocom.org/projects/sdr/wiki/rtl-sdr
        (scroll down to bottom of page to find download link)

        Un-zip RelWithDebInfo.zip. It will create a folder RelWithDebInfo and inside this folder another folder rtl-sdr-release which contains several files and 2 folders named x32 and x64. Open folder x32




        Copy following 3 files of folder x32 into newly created folder RF Scan.
        (1) libusb-1.0.dll
        (2) rtl_power.exe
        (3) rtlsdr.dll





        STEP 5 of 7:
        Download file heatmapĚpy by Right-Clicking on the link below, and choosing "Save Link As..."
        Move the downloaded file heatmapĚpy into folder RF Scan.

        https://raw.githubusercontent.com/ke...map/heatmap.py



        STEP 6 of 7:
        Make sure no program is using DVB-T Dongle. Stop any such program to free DVB-T.

        Open Command console by typing cmd in search. Once the Command Console is open, do following:

        Code:
        # First CD to folder RF Scan
        #Once in folder RF Scan, give following command
        rtl_power -f 800M:1200M:100k -i 30 -c 50% -e 30m -g 30 -F 9 > scan.csv

        The above command will generate following output.




        Wait for 30 minutes for scan to finish.
        When scan is finished, it will say "Exiting.... Canceled by user".
        Scan will create a file "scan.csv" in current folder and save scan data in it.

        This will produce a very wide image (4000 pixels!) that shows spectrum power from 800MHz - 1.2GHz.

        If you want a narrower image, increase “100k” above to something larger, it controls the bandwidth that corresponds to one pixel on the x axis.
        -i controls the integration interval (time for one pixel on the y axis)
        -e is the total runtime, longer gives you a taller image.




        STEP-7 of 7:
        Create an image "scan.png" in current folder from data stored in file "scan.csv"
        Open Command console by typing cmd in search. Once the Command Console is open, do following:

        Code:
        # First CD to folder RF Scan
        #Once in folder RF Scan, give following command
        heatmap.py scan.csv scan.png
        The above command will generate following output.



        This will produce a very wide image (4000 pixels!) that shows spectrum power from 800MHz - 1.2GHz.


        Example of Scan of Existing RF Signals by rtl-power




        This image is very wide (4000 pixel), but displayed smaller. As a result details are not clear.
        Click over it to see bigger size.


        Three 500 pixel wide cut-outs from above 4000 pixel wide image. These cutouts show details better.







        Last edited by abcd567; 2018-04-13, 15:11.

        Comment


        • #5
          SWEEP/SCAN BY NOISE GENERATOR

          Image 1 of 6 : SETUP


          .

          Image 2 of 6: Noise Source BG7TBL


          .

          Image 3 of 6 : Pro Stick (orange)


          .

          Image 4 of 6 : Pro Stick (orange) + Filter


          .

          Image 5 of 6 : Pro Stick PLUS (blue)


          .

          Image 6 of 6 : Pro Stick PLUS (blue) + Filter


          .
          Last edited by abcd567; 2018-04-13, 15:06.

          Comment


          • #6
            So the above images show that the internal filter of Pro Stick Plus is not so good as Pro Stick Plus AND an additional external filter?

            If yes: do I understand it correctly that the additional external filter does not put down the signal strength?

            The external filter is the one in image 1 which can be normaly baught for the orange stick?

            Comment


            • #7
              Originally posted by mibock View Post
              So the above images show that the internal filter of Pro Stick Plus is not so good as Pro Stick Plus AND an additional external filter?
              Not in all situations/locations. It depends on what Cell/Mobile signals that particular location has. In large number of locations, the internal filter of ProStick Plus is sufficient. In equally large number of locations, the internal filter is not sufficient and external filter improves reception. Only after adding an external filter one can say for sure if it helped or not.


              If yes: do I understand it correctly that the additional external filter does not put down the signal strength?
              Adding a filter does put down signal, but not much. Also since there is a built-in amplifier in ProStick, it easily overcomes this small loss.


              The external filter is the one in image 1 which can be normaly baught for the orange stick?
              YES, the blue cylindrical thing connected to orange prostick in img-1 is the external filter.
              You can buy the external filter with ProStick, or separately.
              You can also buy other makes of filters available on line on their sites, or on eBay and Amazon.

              Comment


              • #8
                I have a Pro + and still had huge noise at the 820 to 860 and 940 to 960 range. I added the FA filter and it does knock out the cell signals in the 800 range, but not a lot from the 900. This still allowed me to see aircraft further out with higher accuracy (less sporadic drop outs). I am receiving over 200Nm in some area's.

                I will add in my SAW filter soon (once i can find the sma connectors) and hopefully see the 900 signals reduce as well.

                abcd567 is correct with saying that you will more than likely need to drop your gain to reduce the overload, i have dropped mine from 49 to around 30 atm and haven't lost any range , probably gained a little more hits tbh.

                Comment


                • #9
                  Followed Option 1 here and here is the results:

                  Full scan:
                  scan.jpg

                  Part 1
                  1.jpg

                  Part 2
                  2.jpg

                  Part 3
                  3.jpg


                  As I see nothing is interfering 1090 MHz signals?

                  Comment


                  • #10
                    The scan shows that you have strong cell/mobilesignals between 925 mhz and 960 Mhz. This is the interfering signal.

                    Comment


                    • #11
                      Can a filter improve my 1090 Mhz signals? Does this effect my 1090 Mhz reception? Sorry if it is a stupid question .
                      I thought if there is no interference around 1090 Mhz then nothing to worry?

                      Comment


                      • #12
                        The strong cell/mobile frequencies overload the dongle, and performance drops. Removing/reducing these cell/mobile signals improves reception of weak signals from far away planes.

                        Since 960 Mhz is very close to 1090Mhz, you will need a good filter to remove it.

                        EDIT:
                        The flightaware filter is good in removing cell/mobile signals in 850 mhz band, but is not effective in removing cell/mibile signals in 960 mhz band. You may need a SAW filter, or Ceramic filter, or Cavity filter to remove 960 mhz band.
                        Last edited by abcd567; 2018-09-16, 13:35.

                        Comment


                        • #13
                          Thank you @abcd567, Your the best
                          I am thinking of buying Uputronics 1090MHz ADS-B Filtered Preamp. The Ceramic one is way more expensive then the SAW one.
                          Is it worth it? How better reception do you think can I get with Ceramic filter compared to SAW?

                          Comment


                          • #14
                            Ceramic being too expensive, SAW is a reasonable choice. It should be able to remove cell/mobile signals you have.

                            https://discussions.flightaware.com/...ation/40388/32
                            Last edited by abcd567; 2018-09-16, 16:51.

                            Comment


                            • #15
                              Very useful thread, but buried deep under less important threads. Hard to find.
                              My post has brought it at the top of list for now, but in due course it will get buried again.
                              Last edited by TomNJerry; 2019-06-10, 18:18.

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