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

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    Captain abcd567's Avatar
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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 at 05:48.

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