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  • Originally posted by abcd567 View Post
    SNIP
    P.S. There is a coin sized circular copper plate with 4 copper-wire legs, which I understand is a Balun. Am I right? What is the other bigger dia copper tube at the right hand end?
    If you look at the photos of the commercial one you wil see that it has a similar arangement on the outside of the tube,
    I thought that it was just to re-inforce the tube for the clamp, however it made a big difference to the result (it is 1/4-wavelength long) I have seen other plans with a similar arrangement but without the internal balun, (the coin sized plate is in fact a UK penny as it was all I had to hand at the time!).
    I will try the next one without the upper internal balun and see what effect it has.
    My build was based on the earlier photos, but with all the lengths re-calculated and the 1/4 stub tweaked on the analyser.
    There is still much learning to do as so many people and sites have their own way of building these things, my hope is to provide a tested working design that anyone can copy with basic tools and get good results.
    Using RG402 is far better than mucking about with ordinary coax as it can be pre cut to the exact length and solders easily so it should be more repeatable, in a future post I will detail the tools and methods I used on the MK2 build as I am photographing it stage by stage.
    Ben.
    FR24 F-EGLF1, Blitzortung station 878, OGN Aldersht2, PilotAware PWAldersht, PlanePlotter M7.

    Comment


    • Originally posted by F-EGLF1 View Post
      If you look at the photos of the commercial one you wil see that it has a similar arangement on the outside of the tube,
      I thought that it was just to re-inforce the tube for the clamp, however it made a big difference to the result (it is 1/4-wavelength long) I have seen other plans with a similar arrangement but without the internal balun, (the coin sized plate is in fact a UK penny as it was all I had to hand at the time!).
      I will try the next one without the upper internal balun and see what effect it has.
      My build was based on the earlier photos, but with all the lengths re-calculated and the 1/4 stub tweaked on the analyser.
      There is still much learning to do as so many people and sites have their own way of building these things, my hope is to provide a tested working design that anyone can copy with basic tools and get good results.
      Using RG402 is far better than mucking about with ordinary coax as it can be pre cut to the exact length and solders easily so it should be more repeatable, in a future post I will detail the tools and methods I used on the MK2 build as I am photographing it stage by stage.
      Ben.
      Thanks Ben!
      So the outer copper tube is the "folded skirt".
      Later correction: It is not a "folded skirt". It is sleeve for impedance matching. In monopoles/dipoles, it is also used to reduce their physical length.
      Last edited by abcd567; 2014-05-05, 03:49.

      Comment


      • Great improvement after removing 1 element !
        7.5 element range : reange 1.jpg
        8.5 element range :TEST.jpg
        300km thats great ! (have lot of buildings around ! and no line of sight more than 50 km approx in many directions, and in 300km there is mountain after 5nmi.)
        Thanks sir abcd567 !
        Last edited by charan; 2014-05-04, 03:33.
        RTL SDR : T-VEVZ1

        Comment


        • Originally posted by F-EGLF1 View Post
          If you look at the photos of the commercial one you wil see that it has a similar arangement on the outside of the tube,
          I thought that it was just to re-inforce the tube for the clamp, however it made a big difference to the result (it is 1/4-wavelength long) ............
          Ben.
          I tried to find the function of the large outside copper tube. I could not find it for CoCo, but did find it for monopoles in a book (VHF and UHF Antennas By R. A. Burberry).
          The book shows that for monopoles, it affects impedance matching. Please see below screenshots of the relevant parts of the book below:

          Sleeved Monopole-1.jpg Sleeved Monopole-2.jpg
          Last edited by abcd567; 2014-05-04, 09:14.

          Comment


          • So I'm puzzled why people are getting such bad ranges. I plugged my RTL2832 into the raspberry pi, hooked a 1/4-wave dipole up to a short length of coax, and started dump1090, and was immediately getting detections out to 450km away. Changing out the dipole for a 4-element Franklin gave me out to 475km, and with a preamp I'm now getting slightly over 500km. But this is looking out over open ocean. When I see people getting 100-150km range, I can't but think that it must be a line of sight issue, not an antenna problem.

            The thing is, you don't need a lot of obstructions to cut down on the visible distance a lot. I did a quick calculation and it seems a horizon 1 degree above horizontal (1 degree is about 1/4 of the length of the outer joint on your thumb viewed at arms length distance for most people, so not very much at all) drops the distance at which you can see a plane at 30k ft to ~250km. Unless you live in Kansas, even a pretty open horizon can easily be a few degrees above horizontal and in that case no antenna in the world will give you much more than 100-150km.

            It would probably be a good idea for those that are seeing poor detection range to check their local horizon with http://www.heywhatsthat.com/ if they haven't already. If that shows they only have line of sight to 150km, then there's not much to be done.
            Patrik J. / KB1VGP / FR24 T-PHTO1

            Comment


            • Originally posted by lutorm View Post
              So I'm puzzled why people are getting such bad ranges. I plugged my RTL2832 into the raspberry pi, hooked a 1/4-wave dipole up to a short length of coax, and started dump1090, and was immediately getting detections out to 450km away. Changing out the dipole for a 4-element Franklin gave me out to 475km, and with a preamp I'm now getting slightly over 500km. But this is looking out over open ocean. When I see people getting 100-150km range, I can't but think that it must be a line of sight issue, not an antenna problem.

              The thing is, you don't need a lot of obstructions to cut down on the visible distance a lot. I did a quick calculation and it seems a horizon 1 degree above horizontal (1 degree is about 1/4 of the length of the outer joint on your thumb viewed at arms length distance for most people, so not very much at all) drops the distance at which you can see a plane at 30k ft to ~250km. Unless you live in Kansas, even a pretty open horizon can easily be a few degrees above horizontal and in that case no antenna in the world will give you much more than 100-150km.

              It would probably be a good idea for those that are seeing poor detection range to check their local horizon with http://www.heywhatsthat.com/ if they haven't already. If that shows they only have line of sight to 150km, then there's not much to be done.
              I fully agree with you.
              Later addition:
              My maximum range is along Lake Ontario. Your's is also over ocean. It is likely that water, in addition to providing an unobstructed view of horizon, also contributes to propagation (due to humidity) and gives maximum range.

              .
              Last edited by abcd567; 2014-05-04, 09:33.

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              • .
                Please see images below for abstracts about Collinear antennas from the book ""Antenna Engineering Handbook" by Henry Jasik:

                Collinear Arrays-P1.png Collinear Arrays-P2.png

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                • Here's my horizon. I think I'm lucky to get to 150Nm in any direction!
                  Attached Files
                  T-EGUB1

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                  • Well the aerial has been up for a day and a half now, its not what i was expecting.

                    I have had better range from a 8 element (to be expected) how ever i am actually seeing more aircraft in the range it has than i have from other aerials. So overall its actually very good.
                    3.5copy.jpg

                    Just out of curiosity i am going going to attach it to my radarcape, its currently on a rtl stick on a beaglebone just to see how much difference the input stage and bits actually makes. I will be keeping it in its current location (loft space) for a direct comparison, my normal aerial is on a mast well clear of the house and i wont be going up a ladder just for this
                    Last edited by SpaxmoidJAm; 2014-05-04, 10:47.
                    T-EGLF8

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                    • Also, if you look at the Radiation Pattern..it looks more 'Out than Up'..so the 'larger the antenna' (ie;more elements) the 'Less it sees up yet' ! A couple friends are using dongles and getting 300+Km using 8el collinear '..probably don't want to go any more than that !
                      Capture.JPG
                      F-CYQL1
                      Originally posted by abcd567 View Post
                      .
                      Please see images below for abstracts about Collinear antennas from the book ""Antenna Engineering Handbook" by Henry Jasik:

                      [ATTACH=CONFIG]4016[/ATTACH] [ATTACH=CONFIG]4017[/ATTACH]

                      Comment


                      • Originally posted by trigger View Post
                        Here's my horizon. I think I'm lucky to get to 150Nm in any direction!
                        On heywhatsthat.com, select 'up in the air' (top right of map) then put in 35000 and 40000 feet since that should give an indication of what you would see if the ground was bare (no trees or buildings)
                        (see the image referenced in my sig)

                        Comment


                        • Here is plot of my range based on terrain, from "HeyWhatsThat.com".
                          The blue plot is for 40,000 feet high planes. The yellow plot is for 30,000 feet high planes.

                          I have superimposed on it my measured maximum range (by adsbScop). It is in thin black color lines.
                          There are sharp drops in measured range in various directions, which are due to surrounding tall buildings.

                          The plot by "HeyWhatsThat.com" is almost circular, and does not show any sharp drops in any direction.
                          This indicates that "HeyWhatsThat.com" site only takes into account the natural geographic terrain, and ignores any man-made tall structures.

                          HeyWhatsThat-1.jpg

                          .

                          Comment


                          • Originally posted by abcd567 View Post
                            The plot by "HeyWhatsThat.com" is almost circular, and does not show any sharp drops in any direction.
                            This indicates that "HeyWhatsThat.com" site only takes into account the natural geographic terrain, and ignores any man-made tall structures.
                            That actually looks pretty good. I don't think there are any commonly available topographical sources that include buildings in the ground level. It also does not include trees, which can poke up a fairly significant angle above the ground if your obstructions are within a mile or two. The good thing is that both trees and buildings normally only make a difference if they are close by, which also means elevating the antenna can be effective.

                            Edit: I would also guess that the calculator does not take into account refraction of radio waves, so for long ranges it's probably an underestimate. That would be my guess why your measured range is above the maximum out over the water.
                            Last edited by lutorm; 2014-05-04, 18:50.
                            Patrik J. / KB1VGP / FR24 T-PHTO1

                            Comment


                            • Originally posted by lutorm View Post
                              That actually looks pretty good. I don't think there are any commonly available topographical sources that include buildings in the ground level. It also does not include trees, which can poke up a fairly significant angle above the ground if your obstructions are within a mile or two. The good thing is that both trees and buildings normally only make a difference if they are close by, which also means elevating the antenna can be effective.

                              Edit: I would also guess that the calculator does not take into account refraction of radio waves, so for long ranges it's probably an underestimate. That would be my guess why your measured range is above the maximum out over the water.
                              1) water vapour/spray-fine droplets susspended in air definately cause refraction of electromagnetic waves. An everyday example is Rainbow: different light wavelengths (colours) refracting by different angle causing white sunlight to split in 7 colors. In case of RF, this causes bending along curvature of earth and longer range.

                              2) I live in a tall apartment building surrounded by other tall biildings. From level of my apartment, my antenna cannot "see" the horizon in many directions. If I could install my antenna on roof-top of my building (250 feet above ground level), my antenna will have an unobstructed view of horizon for entire 360 degrees. My building management do not allow residents to install any antenna on roof, or even let it project outside the window . So my antenna is strictly indoors.
                              Last edited by abcd567; 2014-05-04, 21:46.

                              Comment


                              • Originally posted by abcd567 View Post
                                My building management do not allow residents to install any antenna on roof, or even let it project outside the window . So my antenna is strictly indoors.
                                Do you have a balcony that they let you have flowers on? That's a time-honored way of disguising an antenna. Since the ADS-B antennas are pretty small, you wouldn't even need a very tall flower...
                                Patrik J. / KB1VGP / FR24 T-PHTO1

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