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  • Originally posted by abcd567 View Post
    5mm is reasonable & practical. I am using 5mm with good results.
    If you try to reduce it, the stub wires may touch each other & the optimum tap position may shift few mm left or right.
    Best keep it as in your diagram - 5mm.
    Now made it, but not got the R-Pi configured yet, it won't talk to my WiFi dongle, so I am going to have to use a network cable for now, pictures of setup and tap below, I will be ditching the cable between the antennae and the amp just as soon as I can get hold of an SMA M-M coupler.
    image.jpgimage.jpg
    Ben.
    FR24 F-EGLF1, Blitzortung station 878, OGN Aldersht2, PilotAware PWAldersht, PlanePlotter M7.

    Comment


    • Originally posted by charan View Post
      i did not provided any sleeve or balun. can you give me the specs to make balun?
      I never made any balun or seleve myself.
      As far as I know, sleeve should be 1/4 wavelength long (VF=1) and that there is no fixed figure for dia of the sleeve. The sleeve dia should be several times the dia of coaxial cable.

      There are several experienced forum members who have good knowledge & experience on this subject. I hope they will come forward and give you (and me also) good advise about sleeve/balun dimensions.

      Comment


      • Originally posted by F-EGLF1 View Post
        Now made it, but not got the R-Pi configured yet, it won't talk to my WiFi dongle, so I am going to have to use a network cable for now, pictures of setup and tap below, I will be ditching the cable between the antennae and the amp just as soon as I can get hold of an SMA M-M coupler.
        [ATTACH=CONFIG]4148[/ATTACH][ATTACH=CONFIG]4149[/ATTACH]
        Ben.
        Nicely made wire antenna. I really like it.
        All wires are straight without any wrinkles. All bends smooth & perfect 90 degrees, a uniform distance maintained between two parallel wires, half-wavelength limbs are perfectly aligned, and the best is a very neat & elegant cable tap arrangement.

        The gap between impedance matching stub conductors in simulation was "5mm from center-to-center of two parallel wires". I cannot measure it on the photo you have posted, but if you have taken 5mm as the air gap between the two parallel wires, then center-to-center distance will be 5mm+1.5mm=7.5mm. This may somewhat affect optimum position of tap and SWR.
        Last edited by abcd567; 2014-05-22, 16:27.

        Comment


        • Originally posted by abcd567 View Post
          I never made any balun or seleve myself.
          As far as I know, sleeve should be 1/4 wavelength long (VF=1) and that there is no fixed figure for dia of the sleeve. The sleeve dia should be several times the dia of coaxial cable.

          There are several experienced forum members who have good knowledge & experience on this subject. I hope they will come forward and give you (and me also) good advise about sleeve/balun dimensions.
          yes; till then ill use 7 elements wit 1/4 shorted top
          RTL SDR : T-VEVZ1

          Comment


          • Originally posted by abcd567 View Post
            Nicely made wire antenna. I really like it.
            All wires are straight without any wrinkles. All bends smooth & perfect 90 degrees, a uniform distance maintained between two parallel wires, half-wavelength limbs are perfectly aligned, and the best is a very neat & elegant cable tap arrangement.

            The gap between impedance matching stub conductors in simulation was "5mm from center-to-center of two parallel wires". I cannot measure it on the photo you have posted, but if you have taken 5mm as the air gap between the two parallel wires, then center-to-center distance will be 5mm+1.5mm=7.5mm. This may somewhat affect optimum position of tap and SWR.
            Yes the gap is probably slightly large, but this is only a quick trial, the limb measurements I took from the center of the wire, so they should be ok, (5+1.5 is 6.5 in the UK)
            I don't expect any results today as most gliders that dared to go up in this changeable weather we had today will have gone home by now, but I hope to get some tomorrow, it will be interesting to see how it compares to the 8-1/2 CoCo on the other R-Pi.
            Ben.
            FR24 F-EGLF1, Blitzortung station 878, OGN Aldersht2, PilotAware PWAldersht, PlanePlotter M7.

            Comment


            • Originally posted by charan View Post
              yes; till then ill use 7 elements wit 1/4 shorted top
              Charan,
              My apologies for the time this is all taking, but by the end of next week I should have some tested results for the baluns, I finally understood how and why they work, now I just need to make, test and photograph them and the rest of the antennae.
              Ben.
              FR24 F-EGLF1, Blitzortung station 878, OGN Aldersht2, PilotAware PWAldersht, PlanePlotter M7.

              Comment


              • yet more technical obsession! lol a coco is an unbalanced antenna, and as the feeder is Also unbalanced... You don't need a BALUN - which is a joining of two words, balanced and unbalanced.
                Impedance transformers may be what you are looking for... But again this is getting overcomplicated, and I'd suggest all this faffery is introducing more losses than the problem you are trying to solve.

                Sent using Tapatalk from my ZX81

                Comment


                • Originally posted by Rooster View Post
                  yet more technical obsession! lol a coco is an unbalanced antenna, and as the feeder is Also unbalanced... You don't need a BALUN - which is a joining of two words, balanced and unbalanced.
                  Impedance transformers may be what you are looking for... But again this is getting overcomplicated, and I'd suggest all this faffery is introducing more losses than the problem you are trying to solve.

                  Sent using Tapatalk from my ZX81
                  If they are not as you suggest needed, then why do the commercial ones have them, you cannot just connect a CoCo to a random length of coax and expect it to perform at its best without them as I have discovered.
                  Also some of us ENJOY the technical challenges, if you are happy with what you have got then good for you, some of us like to tinker, it keeps the grey matter from turning to mush...
                  Ben. (Obsessed and proud of it!)

                  NB according to the Antenna handbook (5th edition) a balun IS an impedance transformer.
                  Last edited by F-EGLF1; 2014-05-22, 17:06. Reason: Added note
                  FR24 F-EGLF1, Blitzortung station 878, OGN Aldersht2, PilotAware PWAldersht, PlanePlotter M7.

                  Comment


                  • Originally posted by F-EGLF1 View Post
                    Charan,
                    My apologies for the time this is all taking, but by the end of next week I should have some tested results for the baluns, I finally understood how and why they work, now I just need to make, test and photograph them and the rest of the antennae.
                    Ben.
                    Hello Ben; no problem at all take your time. i hope you will get the best results
                    RTL SDR : T-VEVZ1

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                    • the posts for making a strait forward aerial will come, I just have to find the time to put together something worth posting.

                      and to be fair this thread has turned a little advanced learning channel, I've only just had my eye's open to the world of aerials and its all very fascinating.
                      T-EGLF8

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                      • Originally posted by F-EGLF1 View Post
                        .....(5+1.5 is 6.5 in the UK).....
                        Ben.
                        But in Canada 5+1.5=7.5 if the person making calculations did not have good sleep last night

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                        • Arrrr, the wonders of alcohol ;-) lol

                          Sent using Tapatalk from my ZX81

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                          • Originally posted by Rooster View Post
                            Arrrr, the wonders of alcohol ;-) lol

                            Sent using Tapatalk from my ZX81
                            lol

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                            • An interesting & easy article about baluns:
                              Antenna Theory - Baluns - http://www.antenna-theory.com/definitions/balun.php

                              Comment


                              • Originally posted by Rooster View Post
                                yet more technical obsession! lol a coco is an unbalanced antenna, and as the feeder is Also unbalanced... You don't need a BALUN - which is a joining of two words, balanced and unbalanced.
                                Impedance transformers may be what you are looking for... But again this is getting overcomplicated, and I'd suggest all this faffery is introducing more losses than the problem you are trying to solve.

                                Sent using Tapatalk from my ZX81
                                CoCo is a balanced antenna. It is a dipole, two equal legs, physically merged, but electrically separate. Since it is end fed, it gives an impression of a whip antenna which is a mono-pole and hence is unbalanced.

                                Example: 8-element coco.
                                Leg 1: Radiating part comprises of shields of odd elements (1, 3, 5, & 7), phasing part comprises of central wire of even elements (2, 4, 6, & 8)
                                Leg 2: Radiating part comprises of shields of even elements (2, 4, 6, & 8), phasing part comprises of central wire of odd elements (1, 3, 5, & 7).

                                Please see sketch below.



                                .
                                Last edited by abcd567; 2014-05-23, 07:42.

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