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  • Originally posted by Rooster View Post
    I said this before, and Ill say it again...

    You are using a VERY large hammer to crack the nut !
    I'd bet that if you took a straw poll, 99% of the forum users couldn't care less about the "rocket science"... they only want to knock up a working antenna.
    Matching feeder to antenna at these frequencies requires an accuracy few could attain, so is basically a waste of effort - without the correct test equipment totally pointless.

    When I first got my TV dongle, I made a coco out of spare satellite cable... no idea of specs whatsoever ! 11cm a section.... fed with an old tv coax feed into the shack (again, zero maths)

    Compared to a commercially built active scanner antenna (same feeder) the coco provides more than 10dB gain over the scanner antenna.

    So YES you can lash up a good antenna with nothing more than a tape measure.
    But there is the challenge of getting something to work better. Pushing the boundaries. It's what humans are made for.
    T-EGUB1

    Comment


    • Originally posted by Rooster View Post
      I said this before, and Ill say it again...

      You are using a VERY large hammer to crack the nut !
      I'd bet that if you took a straw poll, 99% of the forum users couldn't care less about the "rocket science"... they only want to knock up a working antenna.
      Matching feeder to antenna at these frequencies requires an accuracy few could attain, so is basically a waste of effort - without the correct test equipment totally pointless.

      When I first got my TV dongle, I made a coco out of spare satellite cable... no idea of specs whatsoever ! 11cm a section.... fed with an old tv coax feed into the shack (again, zero maths)

      Compared to a commercially built active scanner antenna (same feeder) the coco provides more than 10dB gain over the scanner antenna.

      So YES you can lash up a good antenna with nothing more than a tape measure.
      Originally posted by peterhr View Post
      This is exactly why - for newbies - I suggest making up a dipole and to tie it to a gallows made of bamboo cane.

      The cost is just some old coax (they might have in the shed), some cane (from the garden)

      Fix it to the spouting / guttering at the roof edge so it's as high up as possible and vertical

      The only things to be careful of are not a long down lead (5m or so is ok), and getting decent connectors to adapt the coax to the MCX input on the dongle.

      This will give up to 200nm / 350km range

      Then think about something better.

      For people in high rises there are special considerations...

      They will get the benefit from the height, but are disadvantaged by having to work behind glass (with whatever coatings it has to reflect various wavelengths for heat retention) and a restricted view (unless they can see out of all sides of the building)
      Originally posted by trigger View Post
      But there is the challenge of getting something to work better. Pushing the boundaries. It's what humans are made for.
      Yes, very true.. meeting the challenge..getting something work better.

      The topic of this thread is not "a working antenna" or "an easy DIY antenna" or "a good antenna'. It is "BEST ANTENNA"... a never ending topic with continous effort to improve .... like from walking to horse riding to railways to cars to airplanes to space craft... meeting the challenge....never ending quest for the best...that is what makes humans superior to all living things on this planet.

      Comment


      • Thanks Rooster, peterhr, and trigger for your opinions.
        Yes, we have to strike a balance.

        We should look for the "best" but prime objective should be to keep making the antenna for novice "easy & practical".
        What I am struggling to find a way to tame the wild CoCo (most novice got poor results, few lucky ones moderate to good results). This can only be done if we are able to analyze and understand it, and then try various ways to tame it.

        Comment


        • Originally posted by Rooster View Post
          ........I'd bet that if you took a straw poll, 99% of the forum users couldn't care less about the "rocket science"... they only want to knock up a working antenna.......
          I fully agree to the part of your reply quoted above. That is why I have posted 1/2 wavelength dipole (my very fitst post in this forum) & the Cantenna without mentioning any maths or theory, though I myself had to go through it before I made those antennas.

          .....So YES you can lash up a good antenna with nothing more than a tape measure....
          The failure of most novice to get good results from collinears like CoCo & Frankline contradicts your statement quoted above.

          The reason for tricky nature of collinears stems from:

          (1) Their performance is profoundly sensetive to dimensions due to phasing involved.

          (1) These have high complex impedance (several hundred ohms, resistive+reactive) compared to the Coaxial feeder & receiver (75 or 50 ohms, predominantly resistive).

          Above two characterstics require impedance matching techniques to be incorporated (either as part of the antenna or a separate matching unit) to get a good performance. This results in "maths" & "rocket-science" to jump-in. This makes "lashing up a good antenna with nothing more than a tape measure" very difficult and a matter of chance only.

          With all above difficulties, I still want to come up with good antenna designs which:

          (1) can be lashed up with nothing more than a tape measure.

          (2) uses the most commonly and readily available, low cost materials to make it.

          1/2 wavelength dipole & cantenna are examples of this approach.

          Although at this stage of taming the CoCo, I am involved in theory & maths, and exploring all options including difficult ones, once I find a solution, I will post it in a simple way without rocket science : ) as I have done it for Cantenna & Dipole.

          Comment


          • We are strugling with 1 Ghz wireless antenna, while others have started using 60 Ghz wireless.

            Click here: 60 GHz WiFi

            Comment


            • An analogy to what we are trying to do with taming of CoCo:

              A virus infected patient receives following simple instructions from a doctor:

              Antibiotic "xyz" 500mg capsules every 8 hours, for 5 days.

              The patient follows these simple instruction and gets cured.

              Before the doctor could write the above prescription, a full team of scientists, doctors, biologists, biochemists etc have conducted xfundamental reasearch & experiments on the virus & the antibiotic medicine "xyz" for several years.

              The paitient is never given, nor is interested, in the sceintific details, but wont get this medication if the research was not conducted.

              Comment


              • Empirical, No-Math, CoCo Experiment

                I am planning to do following experiment (when I find free time):

                Make and try a new 8 and 1/2 element shorted top CoCo with different lengths of top 1/2 element.

                CoCo made of RG6 cable (FPE insulation, 0.83 VF).
                The full elements length = 1/2 x 275 x 0.83 = 114 mm.
                The top half elements length = 1/2 x 114 = 57 mm.

                Since top shorted element modifies the SWR, I will make many pieces of 1/2 element with length varying in steps of 5 mm i.e. 57mm, 52mm, 47mm, and 42mm and try the coco by changing top element, to find out which one gives the best range.

                simulation result

                Comment


                • Since top shorted element modifies the SWR, I will make many pieces of 1/2 element with length varying in steps of 5 mm i.e. 57mm, 52mm, 47mm, and 42mm and try the coco by changing top element, to find out which one gives the best range.
                  Or, make ONE 57mm - and trim it ! LOL

                  Comment


                  • Originally posted by Rooster View Post
                    Or, make ONE 57mm - and trim it ! LOL
                    Yes, an easier option. Thanks.

                    After fabrication & trial run of over half a dozen miserably failed CoCos, I really dont feel any appetite to go through this distasteful experience once again.

                    Comment


                    • Yes I was surprised to see so much discussion about the coco especially after the failed attempts in the past. I still reckon my whip design is the easiest to reproduce over and over again, and know its right. All thats needed is to follow the formulas for wavelength, with no alterations for velocity effect. The problem is acquiring the fibreglass blanks
                      Mike

                      PS abcd did you get to do my extended whip on 4nec2? You were going to show me how to add elements / coils to the YWYY_double_whip
                      Last edited by YWYY; 2014-10-25, 10:45.

                      Comment


                      • Originally posted by YWYY View Post
                        .....PS abcd did you get to do my extended whip on 4nec2? You were going to show me how to add elements / coils to the YWYY_double_whip
                        Sorry, I forgot .... will do as soon as I find time

                        Yes I was surprised to see so much discussion about the coco especially after the failed attempts in the past. I still reckon my whip design is the easiest to reproduce over and over again, and know its right. All thats needed is to follow the formulas for wavelength, with no alterations for velocity effect. The problem is acquiring the fibreglass blanks
                        Mike
                        Apparently true, but as deceptive as the CoCo.

                        Both theory and simulation show that the antenna's performance (SWR & Gain) are very sensitive to coil diameter (equal to the diameter of the fiberglass whip on which the coil is wound) AND the coil length.

                        If a US whip is used, it will be 1/4 inch = 6.4 mm dia. If European (metric) whip is used, it will be 6mm dia. There will be profound change in SWR due to this little change of dia. Similarly if you change the coil length by compressing or expanding the coil a few mm, this will also have profound effect on SWR.

                        But your design has advantage over CoCo of possibility of some adjustment by trimming the top element's length.

                        Later additon: If heat shrink tube is not applied, the antenna can be tuned (i.e. SWR & Gain can be adjusted) by expanding or compressing the coil.
                        Last edited by abcd567; 2014-10-25, 22:39.

                        Comment


                        • Originally posted by YWYY View Post
                          .....abcd did you get to do my extended whip on 4nec2? You were going to show me how to add elements / coils to the YWYY_double_whip
                          Click the links below to download .nec files for 2, 3 & 4 coiled whips.
                          There is negligible advantage in having more than 3 coils.

                          ywyy whip - 2 coils.zip

                          ywyy whip - 3 coils.zip

                          ywyy whip - 4 coils.zip

                          Comment


                          • Various methods of reducing SWR of CoCos
                            Verified by Simulation.
                            Verification by making these CoCos and putting these to trial run is yet to be done.


                            4 Element CoCo from RG6, FPE insulation, 0.83 VF
                            # Number of Full Elements Impedance Matching Element SWR GAIN dBi
                            (in Hoizontal Direction)
                            (1) 4 elements 114mm NIL 5.03 6.13
                            (2) 4 elements 114mm Above 4th element - 57mm Coax, shorted top (1/4 wavelength) 3.04 4.09
                            (3) 4 elements 114mm Above 4th element - trimmed (35mm) Coax, shorted top 2.75 5.18
                            (4) 4 elements 114mm Below 1st (bottom) element - 35 mm Coax, shield removed and replaced by single wire new-animated-1.gif
                            (see sketch below)
                            1.66 5.68

                            Twin Wire TL Matching.jpg
                            Last edited by abcd567; 2014-10-27, 04:45.

                            Comment


                            • Thanks mate I appreciate your work
                              Mike

                              Comment


                              • I have made a new 4-Element CoCo from RG6 and put to trial run now.

                                (1) Under trial run now: 4 elements 114mm, No matching element.

                                (2) Next trial run will be: 4 elements 114mm + 57mm, shorted element at top.

                                (3) Next trial run will be: 4 elements 114mm + trimmed (35mm), shorted element at top.

                                (4) Last trial run will be: 4 elements 114mm + 35mm, shield removed, between lowest element & feed line. (refer to post#1795 item#4)

                                DSC03398-R.jpg . DSC03395.jpg
                                Last edited by abcd567; 2014-10-27, 18:15.

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