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New to the field of SDR and ADS-B - Questions about antennas and reception

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  • New to the field of SDR and ADS-B - Questions about antennas and reception

    Hi,

    Being new to the ADS-B specifically and to the SDR in general, I watched lots of videos and red lots of forum posts about software and antennas and tried to make my own antenna instead of using the antenna shipped with the RTL-SDR blog V4.

    This is my ugly spider (or should I say "ground plane") antenna made of wireless cable for outdoor installations (the core is 2.7mm thick) which I think has an impedance of 50Ω.

    It is installed temporary in my Attic which has walls made of bricks and a wooden roof covered with metal sheets. It is placed on a metallic mast in front of a door made of metal (also) and glass. It is the worst possible installation for an antenna, I know.

    I would like to ask if someone has any suggestion to improve this antenna or to make another one (I have also made one with 8 legs using outdoor cable for TV antennas of 75Ω but it's not performing well)

    I am next to a big airport (Athens - Greece) but the area has hills and mountains so the visibility isn't the best possible but I have received airplanes from 260Km afar or even further but only from specific directions due to the obstacles (and probably because the antenna is indoors).​

    I'm also thinking of a CoCo (coaxial-collinear) antenna construction, any suggestion of a good trusted and testes DIY antenna of this kind ? Would it perform better than a spider ?​

    Thanks in advance for your help and suggestions.

    Nikolas 20240528_122906 (Large).jpg

  • #2
    And these are another two I made from posts in this forum I think. Not performing well though. So far only the spider with four legs is the winner. I think because of the very good cable I used (it was purchased years ago when I installed a WiFi long range link).

    I have also ordered a LNA+AMP from China because my area is "polluted" from many GSM stations and I also have a NATO long range communication installation with dozens of huge antennas just next to me.

    This is more or less what I see from my place and with current installation.

    image.png
    Attached Files
    Last edited by nikall; 2024-05-28, 10:11.

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    • #3
      The important thing is NOT which size of wire you use for making the whip and legs of a Spider. The spider performs nearly same with different sizer of wire used to make it.

      The important thing is the type and length of coax cable between Spider and the dongle (SDR).

      There is a loss of signal (attenuation) when travelling through coax from Spider to SDR.

      The total loss of signal= attenuation / meter X length of coax in meters

      If coax cable has high attenuation per meter, and/or the length of cable is big, total loss will be high and performance will go down.

      Another very important thing is that all the legs are electrically connected to sheath / braid of coax. If not, performance will go down. You can check this by a continuity meter or multitester.

      ​​​​​​​
      Last edited by abcd567; 2024-05-28, 17:39.

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      • #4
        Originally posted by abcd567 View Post
        The important thing is NOT which size of wire you use for making the whip and legs of a Spider. The spider performs nearly same with different sizer of wire used to make it.

        The important thing is the type and length of coax cable between Spider and the dongle (SDR).

        There is a loss of signal (attenuation) when travelling through coax from Spider to SDR.

        The total loss of signal= attenuation / meter X length of coax in meters

        If coax cable has high attenuation per meter, and/or the length of cable is big, total loss will be high and performance will go down.

        Another very important thing is that all the legs are electrically connected to sheath / braid of coax. If not, performance will go down. You can check this by a continuity meter or multitester.

        ​​​​​​​
        Thanks for the reply. Yes I know the basic theory for RF. Well, I still don't have cables to be honest. I do everything with any leftover of cable I had around. What I miss the most is a good set of adapters and connectors. Could you please suggest where to buy a good set of various adapters/connectors ? I'm looking in China mostly but I need some guidance on what type of each connector/adapter. What is used most of the times so to buy more pieces.

        Also, I'm thinking of using those leftover cables to make more antennas. Do you have some design suggestion ? Preferably something easy for a beginner (this coax/colin antenna, any schematics to make one ?).

        thanks in advance for your help and time.

        Nikolas

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        • #5
          Coaxial Collinear antenna, also known as CoCo antenna is easy to make, but difficult to get right without using sophesticated test equipment. As most hobbyist neither have these equipment, nor skill to use these, making CoCo is a shot in dark. Few lucky ones get good results, while most end up in a lousy antenna.

          Try this one, it is easy to make.

          QUICK SPIDER - No Soldering, No Connector



          .
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          • #6
            Originally posted by nikall View Post

            What I miss the most is a good set of adapters and connectors. Could you please suggest where to buy a good set of various adapters/connectors ? I'm looking in China mostly but I need some guidance on what type of each connector/adapter. What is used most of the times so to buy more pieces.

            The connector at the SDR end of cable depends on two things:
            (1) Type of cable
            (2) Model of SDR. Some SDRs require mcx-male, some other require sma-male

            You can find almost all types of connectors, adaptors and pigtails on

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