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  • Originally posted by Rooster View Post
    The trap that is so easy to fall into here is to add an amplifier INSTEAD of improving the antenna system !

    The best thing to do is install a better antenna, then better feeder... or even remove the feeder (ive had success with a TV dongle at the base of the antenna, using CAT5 cable + USB extenders back to the shack)

    But this is a double edged sword... the better the antenna system the more noise it 'could' gather...

    Id advise ONLY using amps to overcome cable loss.
    To have a better antenna under DIY is something very difficult to achieve for a novice. In fact most of them end up in poor DIY antenna rather than better DIY antenna. The solution is to purchase a commercial antenna, but again this option is out of budget for most novice who go for cheap equipment like $9 DVB-T USB Dongle from China. The in line amplifier is a via media: reasonable cost and reasonable results. That is why it is so popular.

    As you mentioned rightly, better antenna picks up more noise as well. But it is not only noise, it also picks up same signal twice, a direct one and another reflected & weak one (Ghosting). Same is the case with amplifier. It amplifies the noise and the ghost signal as well. So both the good antenna & amplifier are double-edged sword.

    However the amplifier has one disadvantage compared to a good antenna: In addition to amplifying the external noise picked up by antenna, the amplifier itself generates noise (3 dB to 7 dB for normal satellite amplifiers), while antenna does not generate any noise, it only picks up external noise. Here a good antenna wins over an amplifier.

    Comment


    • 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

      Comment


      • 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.

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