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  • Could you shed a little more light on your design, I'm not quite getting how you going to keep the two half waves away from the quarter.

    i have access to a VNA so i could test it.
    T-EGLF8

    Comment


    • Sorry for not answering sooner... business is taking over ... as well as preparing flying since decent weather is on its way :-)

      The idea of the above design is to use the work developed by the authors in the links below.
      The simplest form of a collinear is to have stacked vertical half waves that radiates in phase, separated vertically by approx half wave.
      The simplest solution to feed (connect) the radiating vertical half waves in phase is to use a very thin wire which is also a half wave. The radiating half waves are large diameter and the phase lines are small diameter.
      If the large diameter elements are in phase and the small diameter elements are out of phase with the large diameter elements, radiation from the large diameter elements dominate.
      Because the antenna is for receiving only, the phasing lines can use very small diameter without introducing any significant loss.

      On the drawing, the lower half wave is center feed which makes matching to 50-75 Ohms more easy.
      Using large diameter copper for the radiating elements helps reduce the antenna impedance at resonance and accentuate the ratio between radiating and phasing elements diameters to further minimize radiation from phasing lines.
      You can see the lower half wave like the spider antenna which has been described before, at the end of which is connected a half wave phasing line which is connected to a half wave large diameter radiating line.
      Adjusting the angle of the "spider legs" allows to adjust the impedance at resonance.
      The below antenna should provide around 2-3 dB of gain compared to the spider antenna.
      To improve radiation pattern, it might be a good idea to add a second ground plane, a quarter wave below the feed point of the lower half wave (65-70 mm below in our case).
      coli jld2.png
      Adding 3 radiating half waves above the spider should provide 5-6 dB of gain compared to the spider antenna.
      In order to improve further the low angle radiation, it would be worth to try reducing progressively the diameter of the radiating elements (for example 10mm, 8mm, 6mm and 4mm for a 4 half wave vertical)
      coli jld3.png
      All this is theory and should be validated by experimentation.
      The beauty compared to the coaxial version is that it does not depend from coaxial cable VF and it should be easy to construct with repeatable performance.

      https://www.engr.colostate.edu/~nota...20Antennas.pdf
      http://home.comcast.net/~ross_anderson/sc.htm

      Comment


      • Hallo,

        i build one of these cantennas for my Raspberry PI & DVB-T Stick Combo. It works good. With the antenna from the stick i got 4-6 planes, now i have 15 planes...

        When the WiFi modules arrives i will place the reciever in a other room...

        Happy Easter
        Last edited by borchi; 2015-04-04, 12:03.
        Christian


        openspotter.org - Aviation Photography | Förderverein Rosinenbomber e.V.

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        • Jld,
          An interesting design, however it would be wrong to call it a collinear as it is effectively a single wire, in operation it would be more akin to a single ended franklin with the phasing stubs straightened out, you could make this more compact and possibly better performing by folding the phasing stubs out at 90 degrees and coiling them round in 7/8th of a circle.
          That would almost half the overall length, and you could still run a glass fibre pole through the center of it for support.
          One additional problem that I can see is that the large diameter elements make this quite wideband so you may pick up out of band signals and overload the front end if you use it with an RTL dongle or similar, these tend to work best with a well tuned narrowband antenna.
          Ben.
          FR24 F-EGLF1, Blitzortung station 878, OGN Aldersht2, PilotAware PWAldersht, PlanePlotter M7.

          Comment


          • Originally posted by borchi View Post
            Hallo,

            i build one of these cantennas for my Raspberry PI & DVB-T Stick Combo. It works good. With the antenna from the stick i got 4-6 planes, now i have 15 planes...

            When the WiFi modules arrives i will place the reciever in a other room...

            Happy Easter
            Willkommen an Bord. Suggest you read these threads for Beginners:

            3 EASY ANTENNAS FOR BEGINNERS

            Raspberry Pi: How To Install Raspian OS, Dump1090, FR24 Data Feeder

            Comment


            • @JLD:
              @F-EGLF1
              The design proposed by JLD is worth experimenting. It is a collinear antenna, though looks different from conventional collinears. Antenna height is not a problem as at 1090 MHz the wavelength & hence element length is small. This design most suits Printed Citcuit Board antenna - half wavelength long alternating wide & narrow strips of copper on PCB.
              Last edited by abcd567; 2015-04-05, 03:53.

              Comment


              • A HYBRID OF SPIDER & FRANKLIN
                This is a conceptual design only, not yet built & tested
                Hybrid Spider Antenna SO239 640x1640.jpg
                Last edited by abcd567; 2015-04-06, 16:55.

                Comment


                • @JLD thanks for the info, i get it now. My brain got stuck on a particular path which didn't work for me
                  T-EGLF8

                  Comment


                  • Indeed it is using a similar concept to printed antennas.
                    The reason for this approach is to make something very easy to build which is not sensitive to construction details, while providing gain over dipole or ground plane.

                    The large diameter radiating elements are less sensitive to length since and still provide a rather narrow bandwidth when stacked.
                    They also make the radiating impedance lower which allows to get the ground plane wires closer to vertical, contributing to lower the radiation angle toward the horizon.

                    Phasing lines can be complex to design and build. In your example above, the exact length is probably not a half wave and the diameter of the wire, the radius of the bents and the separation between the horizontal sections play a critical role, making this difficult to build.

                    Also the idea to fold the phasing line is only interesting when it is desired to shorten the physical length of the antenna but it lowers the gain by up to 2dB when stacking 4 half waves.
                    Analysis have shown that the optimum vertical spacing is between .4-.5 wave length separation between the half waves.
                    In your example of three stacked half waves, with close spacing between the vertical half waves, the gain over a single vertical half wave should be 3.5 dB when it would be just above 5db if vertical separation was between .4 and .5 wave length.
                    The is the reason why using the principle of thin wires cut to exactly a half wave length (thin wires have a VF of 1) to create the phasing line should work well, making an easy construct while provide close to optimum spacing to get max gain.

                    Need to leave for airfield now.
                    Will try to build tonight.

                    JL

                    Comment


                    • @JLD:
                      @SpaxmoidJAm:

                      Waiting for test /trial run results after you build it.

                      Comment


                      • @JLD:
                        @SpaxmoidJAm:
                        @F-EGLF1:
                        Simulation of JLD's Thick-Thin wire Collinear (by software 4nec2) :


                        Have a look at the radiation pattern at right side of screenshot

                        Thick Thin Collinear Monopole Short Feed+Groundplane.PNG
                        Last edited by abcd567; 2015-04-06, 17:05.

                        Comment


                        • The length of the elements change with wire/tube diameter (larger diameter wires resonate at a frequency lower than their physical length).
                          I use 4 ground plane 65mm 2.5mm dia
                          first vertical 1/4 wave: 61 mm 10mm dia tube
                          half wave phasing line: 138mm 0.1mm dia wire
                          half wave radiating tube: 122 10mm dia tube
                          the ground plane wires are around 60 deg from vertical for 50 Ohms and 35 deg from vertical for 75 Ohms.
                          return loss is around 20 dB and SWR better than 1.5.

                          I have no way to measure radiation pattern.
                          It is not as good as the 8 elements co linear I already build but this was not supposed to!
                          I will build a small ground plane as a reference antenna and comapre the number of messages I get.

                          JL

                          Comment


                          • @JLD:
                            Thanks for the details of dimensions. I will modify my model accordingly, re-simulate, and post the results.

                            Comment


                            • abcd, what does your software suggest for the performance of that franklin/spider hybrid? It looks like it might be worth a try.

                              Comment


                              • Originally posted by caius View Post
                                abcd, what does your software suggest for the performance of that franklin/spider hybrid? It looks like it might be worth a try.
                                I did not run a simulatuon for it as I had little hope of it's success. I just put is as a concept, as an analogy to JLD's proposal.

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