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  • A question about gain/SWR.
    Whilst I was moving my best 12 element CoCo, I managed to pull a couple of the segments apart . I will repair it tonight but is there anything to be "gained" by adding another 4 elements thus making it a 16 segment one?
    T-EGUB1

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    • Originally posted by trigger View Post
      A question about gain/SWR.
      Whilst I was moving my best 12 element CoCo, I managed to pull a couple of the segments apart . I will repair it tonight but is there anything to be "gained" by adding another 4 elements thus making it a 16 segment one?
      Since your antenna is your best one, it shows it's elements are of optimum length (or very close to optimum). Adding elements will improve gain/swr. If antenna is alresy not good, it's elements are far from optimum, and adding elements will add to this error and may worsten it.

      (2) Doubling the number of elements increases gain by 3 dB. If 4 element is enhanced to 8 element, or 8 element enhanced to 16 element, or 12 element enhanced to 24, gain will improve by 3 dB. Enhancing 12 to 16 element will improve gain by only a fraction of 3 dB.
      Last edited by abcd567; 2014-12-19, 21:30.

      Comment


      • My way of making a CoCo which seems to be repeatable.

        Calculate the length according to the Velocity Factor of the coax. Coco element length = 1/2 x wavelength x VF
        where VF = velocity factor of cable. Add an extra 16mm (8mm for each end)
        There is a table posted by abcd567 further back up this thread but here are some values for VF.

        RG-6/U PE (Belden 8215) 66.0
        RG-6/U Foam (Belden 9290) 81.0
        RG-8/U (PE (Belden 8237) 66.0
        RG-8/U Foam (Belden 8214) 78.0
        RG-8/U (Belden 9913) 84.0
        RG-8X (Belden 9258) 82.0
        RG-11/U Foam HDPE (Beld. 9292) 84.0
        RG-58/U PE (Belden 9201) 66.0
        RG-58A/U Foam (Belden 8219) 73.0
        RG-59A/U PE (Belden 8241) 66.0
        RG-59A/U Foam (Belden 8241F) 78.0
        RG-174 PE (Belden 8216) 66.0
        RG-174 Foam (Belden 7805R) 73.5
        RG-213/U (Belden 8267) 66.0

        LMR-240 84.0
        LMR-240UF 84.0
        LMR-400 85.0
        LMR-400UF 85.0

        Davis BuryFlex 82.0

        I then stick the ends of my voltmeter probes between the shield and the outer insulation.
        1.jpg

        This gives a bit of room and makes it easier to push in the core.
        3.jpg

        I push the 2 pieces together without the insulation between the joints as I found it too fiddly. Leave a gap of about 1mm
        2.jpg

        Tape the joints with some insulation and then check continuity. Continue with each segment and check continuity each time.
        Last edited by trigger; 2014-12-19, 21:51. Reason: typos and addition
        T-EGUB1

        Comment


        • Originally posted by abcd567 View Post
          Since your antenna is your best one, it shows it's elements are of optimum length (or very close to optimum). Adding elements will elemeent, gain wil improve gain/swr. If antenna is alresy not good, it's elements are far from optimum, and adding elements will add to this error and may worsten it.

          (2) Doubling the number of elements increases gain by 3 dB. If 4 element is enhanced to 8 element, or 8 element enhanced to 16 element, or 12 element enhanced to 24, gain will improve by 3 dB. Enhancing 12 to 16 element will improve gain by only a fraction of 3 dB.
          Hi abcd, I've fixed my 12 element CoCo and added a piece of dowel to strengthen it. I'll put it back on test tomorrow. In the mean time I'll make another 12 element and if that one proves to be good too, I'll stick the 2 together
          T-EGUB1

          Comment


          • Originally posted by trigger View Post
            My way of making a CoCo which seems to be repeatable.

            Calculate the length according to the Velocity Factor of the coax and add an extra 16mm (8mm for each end)..................
            Great! This is very helpful for all CoCo maker, new & experienced.

            Comment


            • Originally posted by trigger View Post
              Hi abcd, I've fixed my 12 element CoCo and added a piece of dowel to strengthen it. I'll put it back on test tomorrow. In the mean time I'll make another 12 element and if that one proves to be good too, I'll stick the 2 together
              Good, will keep you busy during this weekend.
              Waiting to see the performance of your new 2-in-1 coco , or do we call it 2-dozen coco?
              Last edited by abcd567; 2014-12-20, 07:14.

              Comment


              • 2x8elements.JPG

                Image1.jpg

                2x STACKED YAGIS

                Mike
                Last edited by YWYY; 2014-12-20, 10:14.

                Comment


                • Originally posted by YWYY View Post
                  [ATTACH=CONFIG]5229[/ATTACH] [ATTACH=CONFIG]5230[/ATTACH]
                  2x STACKED YAGIS
                  Mike
                  Excellent! Gain=15.5 dBi, SWR=1.3
                  Can you please provide details of connection of two antennas with one feeder?

                  Comment


                  • @Mike
                    Nice build. How does it perform? From the plot it should be amazing. Are you trying to improve your range in a particular direction?

                    PS you nicked the 2000th post too !
                    T-EGUB1

                    Comment


                    • Originally posted by trigger View Post
                      Hi abcd, I've fixed my 12 element CoCo and added a piece of dowel to strengthen it. I'll put it back on test tomorrow. In the mean time I'll make another 12 element and if that one proves to be good too, I'll stick the 2 together
                      Quick update ...

                      24 element CoCo is in service and working well. Range doesn't seem to have improved by much but the frames/sec on RTL1090 has gone way over 2000. I've never seen it this high before. The number of aircraft has increased too but I seemto have lost the aircraft on the ground at my local airport. I pick them up at ~1000'

                      The antenna is very unwieldy. I've strapped it to a couple of bits of dowel and then pushed this into a piece of 21mm white plastic pipe. The whole thing sways about in a light breeze . I wonder how it will stand up to a gale
                      T-EGUB1

                      Comment


                      • YWYY, Also curious in so far how do you connect the 2 Yagi's and deal with possible phasing issues.

                        Comment


                        • Originally posted by trigger View Post
                          Quick update ...

                          24 element CoCo is in service.............. The whole thing sways about in a light breeze . I wonder how it will stand up to a gale
                          https://www.youtube.com/watch?v=uY-WpjPZVQY

                          Comment


                          • Originally posted by trigger View Post
                            Quick update ...

                            24 element CoCo is in service and working well. Range doesn't seem to have improved by much but the frames/sec on RTL1090 has gone way over 2000. I've never seen it this high before.
                            Just realised that yesterday was the last Saturday before Xmas and there was a mass exodus of people from the local airports. Much more normal today.

                            @abcd567 mine swings a lot more than that
                            T-EGUB1

                            Comment


                            • Originally posted by abcd567 View Post
                              Excellent! Gain=15.5 dBi, SWR=1.3
                              Can you please provide details of connection of two antennas with one feeder?

                              Hi , I spaced the beams 1.5 wavelengths - thats 275mm x 1.5 = 413mm
                              The feeding harness is made with multiples of 1/4 wave ..... equal lengths from each beam
                              I made mine 12 x 1/4 waves total - thats 6 x 1/4 waves from each beam
                              Remember to calculate the velocity factor of the coax - I used rg58u @ vf 66%
                              So
                              1/4 w x .66 = 69 mm x .66 = 45 mm
                              45 mm x 6 = 270 mm from the beam to the centre of the tee, overall length from beam to beam = 540 mm
                              The spacing between the beams is not important, it wont alter the tuning or swr, but it will alter the gain and the pattern
                              I chose 1.5 wavelengths as it gave the best gain
                              Initial tests show an improved gain over the single beam

                              2x8element.jpg

                              Mike
                              Last edited by YWYY; 2015-01-21, 10:45.

                              Comment


                              • Originally posted by YWYY View Post
                                Hi , I spaced the beams 1.5 wavelengths - thats 275mm x 1.5 = 413mm
                                The feeding harness is made with multiples of 1/4 wave ............
                                Thanks for the detailed information sbout hook-up arrangement/phasing harness.

                                .........Initial tests show an improved gain over the single beam
                                [ATTACH=CONFIG]5232[/ATTACH]
                                Mike
                                308 nm max coverage! Great!

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