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  • FOR NEWBIES: ANTENNA CONCEPTS BY WATER ANALOGY
    Please see sketch below.
    water to antenna analogy.png

    .

    Comment


    • Originally posted by Rooster View Post
      true, but I honestly think all this techno mumbo jumbo is massive overkill... I suspect most users just want to build a working antenna.. the maths just complicates folk to the point of giving up before they start.

      Sent using Tapatalk from my ZX81
      Math, assuming it is correct, never complicates anything! It reveals the truth.

      Comment


      • Originally posted by Exadios View Post
        Math, assuming it is correct, never complicates anything! It reveals the truth.
        unless you are talking about theoretical science... Then it's a smoke screen for "we don't know"! lol

        Sent using Tapatalk from my ZX81

        Comment


        • All the technical stuff to me is unneccesary

          For my own antenna construction I use the simple formula
          300 divide by freq = full wave
          300 divided by 1090 = 275 mm

          so 1 wave = 275mm

          3/4 wave = 206.5 mm
          1/2 wave =137.5mm
          1/4 wave = 68.75 mm


          These are all the measurements you need

          Bottom of antenna -------/////--------------/////--------------/////--------------/////-------------- Top of antenna

          1st element = 68.75mm
          coil = 206.5mm of wire, wound into coil 68mm long
          2nd element = 137.5mm
          coil
          3rd element = 137.5mm
          coil
          4th element = 137.5mm

          Add as many elements / coils as you want




          Above antenna requires 1/4 w ground plane radials

          ADSB ANTENNA.jpg
          Last edited by YWYY; 2014-04-14, 12:40.

          Comment


          • Originally posted by abcd567 View Post


            SCREENSHOT 4 of 4 - Three-and-Half (3.5) Element CoCo - SHORTED TOP
            Gain = 6.7 dBi, SWR = 6.42 (mismatch loss = 3.3 dB)
            Net Gain Seen by Receiver = Antenna Gain - Mismatch Loss = 6.7 - 3.3 = 3.4 dBi
            [ATTACH=CONFIG]3873[/ATTACH]
            Looks just like the antenna used by FR24

            Now we know why the top is shorted !

            http://ads-b.ca/radar-cape-apart.htm
            www.ADS-B.ca

            Comment


            • Originally posted by Exadios View Post
              Math, assuming it is correct, never complicates anything! It reveals the truth.
              Originally posted by Rooster View Post
              unless you are talking about theoretical science... Then it's a smoke screen for "we don't know"! lol

              Sent using Tapatalk from my ZX81
              For persons interested in getting things done, some amount of maths is manageable, but too much of maths is like smoke screen.
              It varies from person to person how much maths is 'too much maths'.

              Mathematics is in fact the set of rules which govern everything in this universe.
              It is the foundation of all sciences, including apparently unrelated sciences like biology.

              Comment


              • Originally posted by 1090 MHz View Post
                Looks just like the antenna used by FR24

                Now we know why the top is shorted !

                http://ads-b.ca/radar-cape-apart.htm
                Yes, this is the conclusion drawn by me also, which I have mentioned in the begining of the post #826, and quote it below:

                "Reading yesterday's results (post # 824) and this post's results clearly show that:

                (1) For antennas having even number of full elements, adding an open or shorted half element (1/4 wave element) worsens it's performance.

                (2) For antennas having odd number of full elements, adding an open half element (1/4 wave element) worsens it's performance, but adding a shorted half element (1/4 wave element) improves it's performance."

                Comment


                • .
                  FOR NEWBIES: ANTENNA CONCEPTS BY WATER ANALOGY

                  Please see sketch below.

                  water to antenna analogy.png



                  .

                  Comment


                  • Originally posted by 1090 MHz View Post
                    Looks just like the antenna used by FR24

                    Now we know why the top is shorted !

                    http://ads-b.ca/radar-cape-apart.htm
                    Thanks @1090MHz.
                    The 3.5 element CoCo I built, tried, and posted in this forum last year, was based on design provided by you through photos in above link to your web page http://ads-b.ca/radar-cape-apart.htm.
                    Thanks for sharing. You deserve to share the credit in the work done by me.

                    Comment


                    • Originally posted by peterhr View Post
                      Have a look at http://adsb.alle.bg/filter/ for designs of antenna filters. [this doesn't look easy!]
                      Originally posted by charan View Post
                      the filter is too complicated
                      This filter requires knowledge of Wave Guides & Cavity Resonators, which are realm of microwave & radar engineers. For an ADS-B hobbyist, this subject is too complicated.

                      Comment


                      • Originally posted by abcd567 View Post
                        This filter requires knowledge of Wave Guides & Cavity Resonators, which are realm of microwave & radar engineers. For an ADS-B hobbyist, this subject is too complicated.
                        Affirm ; i agree with you.!!! but a small doubt what resonator coil (home made) does for the better reception?
                        RTL SDR : T-VEVZ1

                        Comment


                        • Originally posted by abcd567 View Post
                          Yes, this is the conclusion drawn by me also, which I have mentioned in the begining of the post #826, and quote it below:

                          "Reading yesterday's results (post # 824) and this post's results clearly show that:

                          (1) For antennas having even number of full elements, adding an open or shorted half element (1/4 wave element) worsens it's performance.

                          (2) For antennas having odd number of full elements, adding an open half element (1/4 wave element) worsens it's performance, but adding a shorted half element (1/4 wave element) improves it's performance."
                          So what is the final recommendation on making a coco - 7 elements with a shorted 1/2 element at the top ... or do an open topped 8 element?

                          Is there any recommendation for what to do at the bottom for impedance matching if required...?

                          Comment


                          • Originally posted by peterhr View Post
                            So what is the final recommendation on making a coco - 7 elements with a shorted 1/2 element at the top ... or do an open topped 8 element?

                            Is there any recommendation for what to do at the bottom for impedance matching if required...?
                            Tomorrow I will model a 7.5 element CoCo, and post its simulation result. By comparing results of 8 element open top ( post # 824) & 7.5 element shorted top, we can decide.

                            .j
                            Last edited by abcd567; 2014-04-15, 20:12.

                            Comment


                            • Originally posted by peterhr View Post
                              So what is the final recommendation on making a coco - 7 elements with a shorted 1/2 element at the top ... or do an open topped 8 element?

                              Is there any recommendation for what to do at the bottom for impedance matching if required...?
                              Comparison of simulation results shows that 7.5 element shorted top is slightly better than 8 element open top. Please see screenshots below.

                              SCREENSHOT 1 of 2 - Seven-and-Half (7.5) Element CoCo - SHORTED TOP
                              Gain = 9.23 dBi, SWR = 3.87 (mismatch loss = 1.85 dB)
                              Net Gain Seen by Receiver = Antenna Gain - Mismatch Loss = 9.23 - 1.85 = 7.38 dBi

                              coco 7.5 element shorted at top simulation output.png


                              SCREENSHOT 2 of 2 - Eight (8) Element CoCo - Open Top
                              Gain = 9.52 dBi, SWR = 4.63 (mismatch loss = 2.33 dB)
                              Net Gain Seen by Receiver = Antenna Gain - Mismatch Loss = 9.52 - 2.33 = 7.19 dBi

                              coco 8 element simulation output.png


                              .
                              Last edited by abcd567; 2014-04-16, 07:25.

                              Comment


                              • Originally posted by abcd567 View Post
                                Comparison of simulation results shows that 7.5 element shorted top is slightly better than 8 element open top. Please see screenshots below.

                                SCREENSHOT 1 of 2 - Seven-and-Half (7.5) Element CoCo - SHORTED TOP
                                Gain = 9.23 dBi, SWR = 3.87 (mismatch loss = 1.85 dB)
                                Net Gain Seen by Receiver = Antenna Gain - Mismatch Loss = 9.23 - 1.85 = 7.38 dBi

                                [ATTACH=CONFIG]3898[/ATTACH]


                                SCREENSHOT 2 of 2 - Eight (8) Element CoCo - Open Top
                                Gain = 9.52 dBi, SWR = 4.63 (mismatch loss = 2.33 dB)
                                Net Gain Seen by Receiver = Antenna Gain - Mismatch Loss = 9.52 - 2.33 = 7.19 dBi

                                [ATTACH=CONFIG]3899[/ATTACH]


                                .
                                Good work.

                                ...so, if the user wants to use 'Satellite lead' amplifier that requires power up the cable (like one of these http://goo.gl/zDcQiW, with power inserter http://goo.gl/r1YRnx and suitable power supply ) then they might be better off with the eight element open top. This so the antenna does not require anything done to stop the DC power going into the antenna.

                                for a plain coco with no amplifier, then the 7.5 element with a shorted top is better.

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