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  • @bezeefly:
    From Point B in your Camera Photo.

    Spider 2 r.png
    Last edited by abcd567; 2015-01-20, 07:41.

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    • Ground_Plane_05.jpg
      This is correct.
      www.ADS-B.ca

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      • Originally posted by abcd567 View Post
        Thinner the wire used, easier it is to bend with narrow gaps, but antenna is mechanically weaker with thinner wire.

        Thicker wire gives mechanically stronger antenna, but thicker wires are difficult to bend in narrow gaps.
        It's my understanding that the thinner the wire, the narrower the bandwidth; so a thin wire antenna will not only be mechanically weak, but will also require higher precision in measurement - the advantage being better rejection of out-of-band interference.

        On the other hand, thicker wire receives over a larger bandwidth; so has greater tolerance of (small) measurement errors, although perhaps slightly more at risk from interference.

        Is the gap in the stub wires a constant, or is it proportional to the wire diameter?

        Given that rf currents flow on the outside of the wire, I would have thought the latter and if that's the case, for an antenna intended for outdoor use, would it be preferable to opt for something like copper welding rod or even half-inch copper pipe and thus have a greater margin for measurement and construction inaccuracies?

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        • ok, the diameter is 2.25mm, calculated from 4mm˛, got it now
          i need that thickness, because i will install the antenna outdoors.
          do you have calculations for 2,25mm dia?

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          • Its not the thickness that relates to bandwidth... it the ratio between length and diameter, unless you use - say a coke can as the radiator you wont see much difference !

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            • Originally posted by Kato View Post
              .......Is the gap in the stub wires a constant, or is it proportional to the wire diameter?.......
              Originally posted by STR_EDDS View Post
              ok, the diameter is 2.25mm, calculated from 4mm˛, got it now
              i need that thickness, because i will install the antenna outdoors.
              do you have calculations for 2,25mm dia?
              The gap between wires of IMPEDANCE MATCHING stub (the middle one) depends on dia of stub wire:


              diameter of stub wires d 1mm 2mm 2.25mm 3mm
              center to center distance of stub wires S 3mm 6mm 6.5mm 9mm
              surface to surface gap between stub wires (S-d) 2mm 4mm 4.25 6mm


              See calculations below (if you are not allergic to maths )

              The 4 vertical element Franklin antenna with thin wire (3mm - 1 mm dia) has a typical impedance of 415-j430 ohms (obtained by simulation)
              Zant = 415-j430 = √(4152+4352) = 600 ohms
              Zcoax = 75 ohms
              Required impedance of Stub to get impedance match Zstb = √(Zant x Zcoax) = √(600 x 75) = 212 ohms


              From geometry of stub, Zstb = 276 log (2S/d)
              which can be rearranged as S = (d/2) x 10 to power (Zstb/276)

              The Zstb required for impedance matching of 75 ohm coax with 600 ohm antenna is 212 ohms (see calculations above). Using this value of Zstb, and various wire diameters d, the wire spacing S works out to be:

              if d=1mm, S = (1/2) x 10 to power (212/276) = 2.9 mm say 3 mm
              if d=2mm, S = (2/2) x 10 to power (212/276) = 5.9 mm say 6 mm
              if d=2.25mm, S = (2.25/2) x 10 to power (212/276) = 6.6 mm say 6.5 mm
              if d=3mm, S = (3/2) x 10 to power (212/276) = 8.8 mm say 9 mm


              stub wire spacing 1.PNG.png
              Last edited by abcd567; 2015-01-24, 03:31.

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              • Metric Electrical Wire Sizes: Area mm2 & corresponding diameter mm

                Wire Size
                mm2
                1 1.5 2.5 4 6 10 16 25
                Wire Dia
                mm
                1.128 1.382 1.784 2.257 2.764 3.568 4.514 5.642

                American Electrical Wire Sizes: AWG & corresponding diameter mm

                Wire Size
                AWG
                18 16 14 12 10 8 6 4
                Wire Dia
                mm
                1.024 1.291 1.628 2.053 2.588 3.264 4.115 5.19
                Last edited by abcd567; 2015-01-20, 22:55.

                Comment


                • Originally posted by Kato View Post
                  It's my understanding that the thinner the wire, the narrower the bandwidth; so a thin wire antenna will not only be mechanically weak, but will also require higher precision in measurement - the advantage being better rejection of out-of-band interference.

                  On the other hand, thicker wire receives over a larger bandwidth; so has greater tolerance of (small) measurement errors, although perhaps slightly more at risk from interference.

                  Is the gap in the stub wires a constant, or is it proportional to the wire diameter?

                  Given that rf currents flow on the outside of the wire, I would have thought the latter and if that's the case, for an antenna intended for outdoor use, would it be preferable to opt for something like copper welding rod or even half-inch copper pipe and thus have a greater margin for measurement and construction inaccuracies?
                  Originally posted by Rooster View Post
                  Its not the thickness that relates to bandwidth... it the ratio between length and diameter, unless you use - say a coke can as the radiator you wont see much difference !
                  Regarding bandwidth, I fully agree with rooster.

                  Regarding making Franklin with a pipe, it is practically not feasable to use more than 5 or 6 mm dia wire/pipe because of very tiny stub & radiator lengths (frequency is high, 1090 mhz). The technique to use water copper pipes for making antennas at VHF is very successful due to low frequency & hence much bigger dimensions of stubs & radiators running in meters, allowing use of 3/4" (20mm) pipes.

                  Comment


                  • Here're the results of my 8-element coco and spider antennas. Both antennas were connected to an amplifier, placed indoor beside East facing window. It seemed the coco antenna had better coverage and range.

                    vf0.86-8ele-whip-amp-nm-19012015.jpgspider-amp-nm-21012015.jpg

                    Comment


                    • Originally posted by YWYY View Post
                      Hi I have designed and built successfully an 8 element beam for ADSB. It has the same range as my 9 element wire collinear.
                      I have built 2 of these both with identical range - 270nm

                      [ATTACH=CONFIG]5184[/ATTACH]


                      The MMANA files are also attached




                      Mike
                      remove the .txt from this file before using in MMANA
                      Hi, YWYY!

                      What are the specs to build this 8-element beam? Am still on my steep learning curve about antennas, but if I have clear instructions I can "blindly" follow, I can learn more easily.

                      Thanks!

                      Comment


                      • Originally posted by gquejada View Post
                        Hi, YWYY!

                        What are the specs to build this 8-element beam? Am still on my steep learning curve about antennas, but if I have clear instructions I can "blindly" follow, I can learn more easily.

                        Thanks!
                        The spec is included in this post http://forum.flightradar24.com/threa...ll=1#post60390
                        T-EGUB1

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                        • Also here for 2 x 8 element co-phased

                          http://forum.flightradar24.com/threa...ntenna/page200

                          http://forum.flightradar24.com/threa...ntenna/page201

                          Mike
                          Last edited by YWYY; 2015-01-21, 10:44.

                          Comment


                          • Cant remember if i posted this already so i'll post it any way



                            Its for working out the SWR but it will effectively show your tuning.

                            I'm not sure what software he is using but you get the idea of how to do it..
                            T-EGLF8

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                            • Today i tested my new 2,25mm dia franklin antenna.
                              I took the best spot in the nearby region.
                              Weather was cold and windy, after 15min i left

                              Here are the results:

                              -400km peak
                              -~100 Planes at the same time.


                              09 - YEUZj3z.jpg07 - SPruhbQ.jpg10 - XFOQlSq.jpg08 - 1EQFbOo.jpg06 - 2Qq8O1d.jpg

                              link to image albums (higher resolution)

                              http://imgur.com/a/3W9yd
                              http://imgur.com/a/JmhLO/
                              Last edited by STR_EDDS; 2015-01-21, 22:13.

                              Comment


                              • Looks beautiful! ...The antenna and the scenery!
                                toString - London, UK
                                FR24 - T-EGLC55 / PiAware - toString / PlaneFinder - 9008
                                Raspberry Pi B+ | Keedox DVB-T USB RTL-SDR [RTL2832U+R820T] | Stock Antenna

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