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QUICK SPIDER - No Soldering, No Connector

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  • #16
    Originally posted by joni1101 View Post
    Looks like this antenna has very slightly better specs than the Cantenna. Can you affect the impedance by the angle of the spider legs?

    Sent from my Pixel using Tapatalk
    I did not measure the impedance with radials at different angles, only at 45 degree slanting down.
    Theoretically horizontal radials have 32 ohms, 45 degree slanting have about 50 ohms and vertical (i.e. a dipole) have 75 ohms.

    Practically for ADS-B, I compared message rate for horizontal and 45 degree slanting radials, and noticed only slight increase in adsb message rate with slanting radial. Please see this post:

    Why Antennas Have Ground Plane?

    Please note that the instrument I have used measures only VSWR/R/X/Reflection S11.

    It does NOT measure following important parameters:
    1) Antenna Gain
    2) Antenna Directivity/Radiation curve
    3) Common mode/unbalanced currents in feed coax

    The purpose of this instrument is to check:

    (1) At what frequency antenna is tuned. The tuned frequency is where the SWR-Frequency curve is at minimum. If it is tuned at lower than design frequency, trim the whip, if tuned at higher frequency, add a piece to whip.

    (2) How much is VSWR. If measured VSWR is greater than 1.5, than impedance matching devices should be used. Once the VSWR is below 1.5, its actual value does not matter, then it is the Gain and Directivity which really make difference.
    Last edited by abcd567; 2017-01-30, 02:07.

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    • #17
      Originally posted by joni1101 View Post
      Can you affect the impedance by the angle of the spider legs?
      Please see attached photos. Readings are:
      (1) Spider with horizontal radials, z=26, swr=1.9
      (2) Spider with slanting radials 45 degrees, z=67, swr=1.3
      (3) Spider with vertical radials, z=73, swr=2.2

      32501334462_b814ba037c_b.jpg . 32654383295_a06f14e4a4_b.jpg . 31811480314_35dc93800a_b.jpg

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      • #18
        Very interesting. Amazing how these small changes in geometry affect performance. Best bet is 45 seems like?

        Sent from my Pixel using Tapatalk

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        • #19
          Well, I wanted to give it a try as my first ads-b antenna and this tiny GP gave me 500Km (i.e. 270nm) of coverage at the first attempt !!
          I have to admit that my balcony is at 330m above sea level and I only have the ocean in front of me and this helps a lot
          Nevertheless I have no coverage toward the West.
          Im really happy so far but Im already building a J-pole for more coverage before start feeding FR24 with my brand new Orange Pi PC Plus.

          Btw as you can see I kept the cable to the minimum :-)

          IMG_20170426_153009.jpg

          IMG_20170426_194854.jpg

          Thanks abcd567 ;-)
          Orange Pi PC Plus + NooElec NESDR SMArt + homemade 6 ele CoCo

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          • #20
            Do I understand it correctly that

            - the outer wires have no contact to the inner wire?
            - that this kind of antenna helps against doughnut-effect with very near planes during landing and starting?
            - that the blue plastic-thing helps reflect waves from nearby planes?
            - does the blue plastic-thing helps with nearby planes if I put it under the 68cm flight-aware-antenna I have bought?

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            • #21
              Originally posted by mibock View Post
              Do I understand it correctly that

              - the outer wires have no contact to the inner wire?
              Correct.
              The outer wires are connected only to the braid & shield of coax. These have no connection to central wire of coax.

              - that this kind of antenna helps against doughnut-effect with very near planes during landing and starting?
              No, it does not eliminate doughnut effect, but nearby planes are picked somewhat better than a high gain antenna.


              - that the blue plastic-thing helps reflect waves from nearby planes?
              Totally wrong. The blue plastic thing is a support, and does NOT contribute or affect antenna performance


              - does the blue plastic-thing helps with nearby planes if I put it under the 68cm flight-aware-antenna I have bought?
              No, it wont help. It has no effect on antenna performance. It is just a support.
              Last edited by abcd567; 2018-07-18, 15:33.

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              • #22
                Thank you for your answers, abcd567. :-) You seem to be the Mr. Antenna from what I read.

                So I come to my next question:

                what happens if I glue the 45-degree-wires to the outside of my flightaware-antenna? Would I have better reception of near planes?

                It would have no contact like your solution to the inner wire because of outer isolation. :-)

                And a question I posted in my first post in this forum later, where you helped me with installation.

                The landing planes which I do not see are in an angle of about 25 to 35 degress to my position, 500 metres away. I understand if they would fly high above me that the antenna can not get them, but nearly horizontal I do not understand.
                So maybe an additional filter you wrote in the other post from today may help better. I live in Hamburg next to one of the fly-in/out-spots.

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                • #23
                  mibock
                  I never tried glueing radials to Flightaware anena, so cannot tell you anything. You may try it.


                  Following may help

                  (1) Reducing gain setting of dongle. Try different values say 45 , 40, 35, 30,25,and at each gain setting run your pi for some period and watch. Since nearby plane's signal is strong, their signals may not be processd due to overload. Reducing gain may result in the nearby planesalso start showing.

                  (2) Adding a filter.
                  Last edited by abcd567; 2018-07-18, 19:36.

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                  • #24
                    Following abcd567 post I did my own spider antenna. Here it is.
                    I used Thermal tail to isolate metal parts from the rain and also I have lately raised it to get a better performance.

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                    • #25
                      .
                      .

                      GROUNDPLANE ANTENNA MADE OF COAX ONLY - Without SO239 or N-Conector

                      .

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                      • #26
                        Still the best Ant i have made and the best range including against bought ones...

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                        • #27
                          @abcd567
                          when i bulid this anntenn.
                          Do I need a special cable to connect to my nooelec nesdr Mini 2+?
                          Currently I have a reception radius of about 50nm(what is nm suitable?), I would like to expand it, possibly I get the Stuttgart airport in.

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                          • #28
                            Originally posted by Conan_89 View Post
                            @abcd567
                            when i bulid this anntenn.
                            Do I need a special cable to connect to my nooelec nesdr Mini 2+?
                            Yes. The nooelec nesdr Mini 2+ site says:
                            "The connector type on the antenna and USB board is MCX--male MCX on the antenna, female MCX on the SDR"

                            NooElec NESDR Mini 2+.jpg


                            You will need a pigtail to connect the "nooelec nesdr Mini 2+" (MCX female socket) to RG6 cable of Spider (F-male connector)

                            Pigtail F-female to MCX-male Rightangle.jpg OR Pigtail F-female to MCX-male Straight.jpg


                            SEARCH RESULTS ON EBAY GERMANY
                            https://www.ebay.de/sch/i.html?_from...Pigtail&_sop=2

                            SEARCH RESULTS ON AMAZON GERMANY
                            https://www.amazon.de/s/ref=nb_sb_no...MCX+Male+RG316
                            Last edited by abcd567; 2018-08-01, 16:48.

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                            • #29
                              I make one of these which I use with my Jetvision USB dongle connected to my Pi 3 B+. I get three times more position reports and hits and slightly more plane counts and range than the stock antenna.
                              However I am not able to achieve this when i a new one for my second feeder, I tried with 5 new spider.

                              I use the same cable, cable length even place in the same position as the first one and connect it to my first feeder results are not good at all, I get around 20% of what I received with my first antenna.

                              What am I missing? Where should I look to find the problem?

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                              • #30
                                My first try to biuld a anntenn.
                                And the result is:
                                The included mini telescopic antenna has better reception than my built -.-
                                Attached Files

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