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  • On the antenna topic, interesting to find a seller on ebay that sells all the different types of antennas for ADS-B

    http://www.ebay.com/sch/stanislavpal...p2047675.l2562

    Any comments, experience with any of these ?

    Comment


    • Originally posted by HermanZA View Post
      On the antenna topic, interesting to find a seller on ebay that sells all the different types of antennas for ADS-B

      http://www.ebay.com/sch/stanislavpal...p2047675.l2562

      Any comments, experience with any of these ?
      His prices are very good... 15 delivered to the UK ! I couldn't make them at that price...

      Seems pretty honest with the gain figures too... he (?) states:
      Gain 2,3 Dbd

      Note this is Dbd.... which is gain over a dipole, not Dbi - which is an imaginary perfect antenna... this measurement is frowned upon in the Amateur radio world as it always offers a higher gain figure !

      As with anything antenna... the hardware and making the thing weatherproof is the hard bit - the antenna proper is going to be a few pennies worth of copper wire.

      Comment


      • 24 hours Trial Run results
        (1) Antenna under test:
        4-element coco made of RG6 FPE VF=0.83 element length=114
        NO impedance matching arrangement
        NO amplifier
        Connected to receiver+Laptop with 20 ft/6 meter commercial RG6 coax.
        CoCo-4-Element-RG6-114mm-24hrs run-30 Oct 2014-R1.jpg


        (2) Benchmark
        Cantenna (Coke Can) + Amplifier
        Connected to receiver+Desktop with 50 ft/15 meters commercial RG6 coax
        BENCHMARK-1-Cantenna+Amp+50ft 15m Coax to Desktop-24hrs run-30 Oct 2014-R1.PNG


        Now on trial run: same CoCo as above, but 57mm shorted-top element added at top
        Last edited by abcd567; 2014-10-31, 05:47.

        Comment


        • 24 hrs trial run with 1/2 shorted element (57mm) added to 4 element coco of previous post #1800
          Range reduced instead of increasing!! The Dark Art of CoCo Making

          1/2 element added
          DSC03399-R.jpg

          Range of antenna under trial
          CoCo-4-Element-RG6-114mm-24hrs run-31 Oct 2014-R1.jpg

          Range of benchmark antenna
          BENCHMARK-2-Cantenna+Amp+50ft 15m Coax to Desktop-24hrs run-31 Oct 2014-R1.PNG

          Comment


          • abcd567, first of all thank you very much for your explanations and tutorials.
            How do you connect DC power supply to the splitter? You use DC socket, but how do you make the wiring?

            Comment


            • Originally posted by ozanguven View Post
              abcd567, first of all thank you very much for your explanations and tutorials.
              How do you connect DC power supply to the splitter? You use DC socket, but how do you make the wiring?
              Please see self-explanatory photos below.

              Before connecting/soldering coax to DC Barrel Jack, first check polarity on Barrel Jack (i.e. which terminal is positive, which is negative).

              To check polarity, plug-in the adapter in power socket, plug in the adapter's barrel pin into barrel jack, then with a multimeter check voltage and polarity of barrel jack terminals. Normally there are 3 pins. One of these will not show any voltage. leave that pin unconnected. Use the other two pins across which you get DC voltage. Normally center of the barrel pin & barrel socket are positive (+).

              DSC03411-R.jpg . DSC03412-R.jpg

              Comment


              • 4-element CoCo with impedance matching.
                Twin-wire transmission line piece (40 mm long) inserted between bottom element & feed line.
                DSC03414 - R.jpg


                How I determined the length of twin-lead TL?
                Starting point was 4-element's impedance: 180-j180 ohms (from simulation by 4nec2 software).
                Rest is only for those interested in maths & theory (see picture below).
                DSC03417-R.jpg
                Last edited by abcd567; 2014-11-04, 10:31.

                Comment


                • Hi ab cd,

                  Wow, protractor and compasses . I haven't used those since I was at school many years ago. I've seen the Smith chart in various documents but had no idea what it was used for.
                  T-EGUB1

                  Comment


                  • 18 hrs trial run results.
                    4-element CoCo with impedance matching by twin-lead transmission line section.
                    Twin-lead transmission line piece inserted between bottom element & feed line.
                    Result: Improved Performance

                    The twin-lead length:
                    Calculated = 41.6 mm
                    Initial trial length = 40 mm
                    Finally adjusted for best result = 44 mm

                    In order to be sure that good performance is not due to favorable weather conditions, I have put the CoCo & Benchmark antenna on 2nd round of 24 hrs trial run.

                    CoCo under Test
                    DSC03420-R.jpg


                    CoCo Range plot (18 hrs trial run)
                    CoCo-4-Element+42mmTL-RG6-114mm-18hrs run-03 Nov 2014.jpg


                    Benchmark Antenna Range plot (18 hrs trial run)
                    BENCHMARK-4-Cantenna+Amp+50ft 15m Coax to Desktop-18hrs run-03 Nov 2014-R1.PNG
                    Last edited by abcd567; 2014-11-04, 07:44.

                    Comment


                    • 2nd Round of 24 hrs trial run - Good Performance
                      4-element CoCo with impedance matching by twin-lead transmission line section.


                      Good result in 2nd trial eliminates favorable weather conditions as the reason for good results.

                      Next step: Test reproducibility in DIY environment.
                      (1) Make another CoCo with same tape-measure & same coax (RG6 from same reel), and put to trial run.
                      (2) Make another CoCo with same tape-measure, coax RG6, but from another manufacturer, and put to trial run.


                      CoCo Under Test
                      DSC03420-R.jpg


                      CoCo Range plot (24 hrs 2nd trial run)
                      CoCo-4-Element+42mmTL-RG6-114mm-24hrs run-04 Nov 2014.jpg


                      Benchmark Antenna Range plot (24 hrs 2nd trial run)
                      BENCHMARK-5-Cantenna+Amp+50ft 15m Coax to Desktop-24hrs run-04 Nov 2014-R1.PNG
                      Last edited by abcd567; 2014-11-04, 18:19.

                      Comment


                      • abcd: have you tried a 1/4 decoupling sleeve above the feeder? Looks like you're attempting something like it without the sleeve

                        Comment


                        • Originally posted by hikeofyourlife View Post
                          abcd: have you tried a 1/4 decoupling sleeve above the feeder? Looks like you're attempting something like it without the sleeve
                          Decoupling Sleeve, as it's name shows, decouples antenna from unbalaced (common mode) currents on the outer surface of sheath of feeder coax. It helps preventing feeder coax's sheath to distort the radiation pattern, reducing gain & directivity. It does improve performance to some extent, but not fully as it does NOT reduce SWR.

                          It is the high SWR which is the real culprit in case of CoCo and most of other antenas whose elements are considerably longer than1/4 wavelength (coco's elements are 1/2 wavelength, twice of 1/4 wavelength).

                          The piece of twin-lead transmission line on the other hand reduces the SWR considerably. This increases signal flow from antenna to receiver, and far off planes whose signal is weak due to distance, start showing up on the rtl1090 & adsbScope.

                          Comment


                          • Originally posted by hikeofyourlife View Post
                            abcd: have you tried a 1/4 decoupling sleeve above the feeder? Looks like you're attempting something like it without the sleeve
                            What you are refering to is a balun (balance to unbalanced) with no impedance change i.e. it is 1:1

                            Please see my post #1208 about sleeve baluns "Sleeve (bazooka) balun 1:1", Source: ECE Dept, McMaster University, Ontario, Canada. Antenna Lectures by Prof. Natalia K. Nikolova

                            Comment


                            • 4-Element CoCo (made from RG6 coax) with Twin-Lead Transmission Line piece for Impedance Matching

                              Comment


                              • The beauty of Twin-Lead SWR reduction method is that it requires only changing the length of Twin-Lead, while observing the max range & max number of aircraft picked by rtl1090/adsbScope/VRServer.

                                With push-pin construction in above sketch, Twin-Lead's length adjustment is easily achieved by pushing the feeder coax towards CoCo to reduce the length & pulling feeder coax away from CoCo to increase the length.

                                Another beauty of this arrangement is that even if the RG6 coax's exact VF is not known, and the CoCo is made with the element length 114 mm, the SWR can still be reduced to below 2, by adjusting the length of Twin-Lead between 30mm & 60mm.

                                For guidance, a table is given below which shows the optimum length of Twin-Lead for different VF (obtained by simulation).

                                4-Element CoCo, made from RG6 coax, Element Length = 114 mm
                                Coax V.F. Twin-Lead Length
                                (shield-to-shield)
                                SWR Gain dBi
                                0.80 30 mm 1.01 5.5
                                0.81 33 mm 1.14 5.5
                                0.82 37 mm 1.30 5.5
                                0.83 42 mm 1.50 5.5
                                0.84 48 mm 1.71 5.5
                                0.85 57 mm 1.89 5.5
                                Last edited by abcd567; 2014-11-08, 19:30.

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