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  • Originally posted by Rooster View Post
    leaving a gap would incur a phase difference, as the gap would effectively become "feeder".... but:

    I honestly think far too many people are MASSIVELY over thinking this stuff... What is the advantage of covering half the planet? surely the idea is to get many stations covering the globe in" cells"?
    what does one person gain by having massive coverage?

    Sent using Tapatalk from my ZX81
    I just want to see "something".

    All I have now is the antenna that came with the dongle, and I have it perched on my roof with an extension cable going down to my Pi which is currently as close as I can get it without drilling a new hole in my house.

    So, I've built this collinear with 16 sections. I can't really put it super high, I'm going to try to get away with it, but, I'm not sure how far I'll get due to HOA rules.

    I'd like to put it next to my DirecTv dish, and put a label on it saying "Digital Television" or something, so I can "say" it's a DTV antenna. Nobody but me would know the difference.

    Comment


    • Originally posted by glen4cindy View Post
      I just want to see "something".

      All I have now is the antenna that came with the dongle, and I have it perched on my roof with an extension cable going down to my Pi which is currently as close as I can get it without drilling a new hole in my house.

      So, I've built this collinear with 16 sections. I can't really put it super high, I'm going to try to get away with it, but, I'm not sure how far I'll get due to HOA rules.

      I'd like to put it next to my DirecTv dish, and put a label on it saying "Digital Television" or something, so I can "say" it's a DTV antenna. Nobody but me would know the difference.
      I am sure you will get good results. Please post your results in forum.

      You may also try this tiny-tot half-wavelength dipole shown in picture below.

      In picture it is shown with in-line amplifier, but even without amplifier it gives good results. Don't get missguided by it's size. It gives astonishingly good results for it's tiny size.

      Further, you may not have any problem with HOS rules for such a tiny anntena.

      uploadfromtaptalk1389410704752.jpg

      Please see what forum member Mike has said about it:

      Originally posted by mickopla View Post
      .......I made a half wave dipole today and was impressed with the results. Max distance was 320km this without any amp. It does have a very short cable run but still impressive. Also i tried the Coco with the short to braid and also impressive results without an amp. ..........Mike
      .
      Last edited by abcd567; 2014-01-11, 05:49.

      Comment


      • Originally posted by abcd567 View Post
        I am sure you will get good results. Please post your results in forum.

        You may also try this tiny-tot half-wavelength dipole shown in picture below.

        In picture it is shown with in-line amplifier, but even without amplifier it gives good results. Don't get missguided by it's size. It gives astonishingly good results for it's tiny size.

        Further, you may not have any problem with HOS rules for such a tiny anntena.

        [ATTACH]3184[/ATTACH]

        Please see what forum member Mike has said about it:



        .
        Thanks so much for your encouragement. Do you have a source for instructions on that tiny-tot half-wavelength dipole? The dipole looks like each leg is a white length of cable coming off the short length of coax, but, they certainly look too big for one of them to be the center copper conductor.

        I'm certainly interested in trying it.

        Thanks.

        Comment


        • see post 137 in this thread.

          Comment


          • Originally posted by glen4cindy View Post
            Thanks so much for your encouragement. Do you have a source for instructions on that tiny-tot half-wavelength dipole? The dipole looks like each leg is a white length of cable coming off the short length of coax, but, they certainly look too big for one of them to be the center copper conductor.

            I'm certainly interested in trying it.

            Thanks.
            Both legs of dipole are made up of Coaxial Cable's central condutor WITH conductor insulation (that is why the legs look white instead of copper color). The insulation is retained to make the legs mechanically stiffer, and helps in making & keeping legs straight. Additional benefit is that it makes the antenna look beautiful.

            Please see sketch below for construction technique for the Dipole.
            I don't have camera pictures for half-wave dipole construction stages.
            I am posting below camera pictures for construction stages of a larger antenna (Franklin).
            The construction technique is same for both tiny-tot 1/2 wavelength Dipole & massive Franklin. The difference is in dimensions.

            Antenna-Coax-Dipole-Short-Legs-2.jpg Antenna-Franklin-Assembly-Steps-1.jpg Antenna-Franklin-Assembly-Steps-2.jpg Antenna-Franklin-Assembly-Steps-3.jpg Antenna-Franklin-Assembly-Steps-4.jpg
            Last edited by abcd567; 2014-01-11, 18:05.

            Comment


            • IMPROVED RANGE BY CHANGING CONDUCTOR SPACING
              For my Franklin antenna, I was using an impedance matching stub in which spacing between stub conductors was 5mm (due to 5mm spacing of terminal screws in the terminal block for adjusting the tap position).
              I dig-up some theory about impedance matching by stub, and found that if I increase the spacing of stub wires to 10mm, I will get a much better impedance match.
              I increased the spacing to 10mm and put antenna on trial run for 24 hrs. I could gain about 75 to 100 km extra in all directions.

              Below are two coverage screen-shots, one for a 5mm spacing stub, and other for 10mm spacing stub.

              franklin+impedance-matching-OPEN-stub-5mm.jpg . franklin+impedance-matching-OPEN-stub-10mm.jpg

              .
              THEORY & CALCULATIONS

              Stub Calculations.PNG

              For matching impedance of Antenna with impedance of Feed Cable, the quarter-wavelength stub's impedance ZSTB shoul be:
              ZSTB = √ (ZFDR x ZANT)
              For RG-6 cable: ZFDR = 75 Ohms
              For Full-Wavelength Dipole / Franklin Antenna: ZANT = 1600 Ohms
              Hence required stub impedance ZSTB = √ (75 x 1600) = 346 Ohms

              Calculated Stub impedance from itís dimensions
              ZSTB = 276 log10 (2S/d)
              where S = conductor spacing in mm, d = conductor diameter in mm
              Stub conductor is #18 AWG which has a dia of 1mm

              CASE A - 5mm SPACING BETWEEN STUB CONDUCTORS:
              S = 5mm, d=1mm
              Hence ZSTB = 276 log10 (2S/d) = 276 log10 (2x5mm/1mm) = 276 log10 (10) = 276 x1 = 276 Ohms
              Conclusion: Not a good match - 276 Ohms provided vs 346 Ohms required

              CASE B - 10mm SPACING BETWEEN STUB CONDUCTORS:
              S = 10mm, d=1mm
              Hence ZSTB = 276 log10 (2S/d) = 276 log10 (2x10mm/1mm) = 276 log10 (20) = 276 x1.301 = 359 Ohms
              Conclusion: Matched closely - 359 Ohms provided vs 346 Ohms required
              Last edited by abcd567; 2014-01-12, 22:34.

              Comment


              • Originally posted by peterhr View Post
                see post 137 in this thread.
                Also see post 118 & 119 in this thread.

                Comment


                • Originally posted by glen4cindy View Post
                  Thanks so much for your encouragement. Do you have a source for instructions on that tiny-tot half-wavelength dipole? The dipole looks like each leg is a white length of cable coming off the short length of coax, but, they certainly look too big for one of them to be the center copper conductor.

                  I'm certainly interested in trying it.

                  Thanks.
                  @glen4cindy: Do the Sketch & Camera Pictures in my post #605 answer your query, and is it now clear to you how to make a Dipole using coaxial cable?

                  Comment


                  • Originally posted by abcd567 View Post
                    @glen4cindy: Do the Sketch & Camera Pictures in my post #605 answer your query, and is it now clear to you how to make a Dipole using coaxial cable?
                    Yes, these sketch and camera photos are very helpful!

                    I thank you, and I'm thankful that I have more than 1 MCX adapter on the way.

                    Comment


                    • Originally posted by glen4cindy View Post
                      ......... and I'm thankful that I have more than 1 MCX adapter on the way.
                      I did not have the MCX adapter, so I cut the cable from Stock antenna which came with the DVB-T USB Dongle. I got a pig-tail having MCX connector at one end and nothing at the cut-end. I then jointed the free end of pigtail to the RG6 cable from my home-made antenna.

                      Since the cable of the stock antenna is coax, it is a coaxial-to-coaxial joint. Although the pigtail coax is thinner than the antenna coax, the joint woks perfectly well.

                      Later when I purchased 2nd DVB-T Dongle, I again cut the cable from stock antenna, but this time I soldered it to a solderable F-female connector. This one also works perfectly well.

                      See Camera Photos of two arrangements below:

                      Direct joint of MCX pigtail to RG6
                      DSC02555C.GIF

                      Termination of MCX pigtail to solderable F-female connector
                      DSC02844R.jpg
                      Last edited by abcd567; 2014-01-12, 23:10.

                      Comment


                      • Originally posted by abcd567 View Post
                        I did not have the MCX adapter, so I cut the cable from Stock antenna which came with the DVB-T USB Dongle. I got a pig-tail having MCX connector at one end and nothing at the cut-end. I then jointed the free end of pigtail to the RG6 cable from my home-made antenna.
                        I would have thought this would degrade the signal, but, apparently not. My first MCX adapter should be here Wednesday, so I suppose I can wait......

                        Comment


                        • The first simple antenna I made was to
                          strip maybe 80mm of the outer sheath from some co-ax,
                          separate the inner and the outer with the co-ax horizontal pull the inner so it's vertically up, the outer so it's down (after twisting it)
                          chop inner and outer to 66mm long

                          I then mounted it on the end of a gallows made from a 10' bamboo cane and some plant support dowels - so I could stick it higher than I could reach.

                          Comment


                          • Originally posted by glen4cindy View Post
                            I would have thought this would degrade the signal, but, apparently not. My first MCX adapter should be here Wednesday, so I suppose I can wait......
                            At any point where there is a sudden change of dimensions/characteristic of transmission line (coax in this case), there is a some degradation of signal due to reflections.
                            Since adapters do the same thing as a direct joint (connect enter-to-center, braid-to-braid with different dia of braid), the direct joint will not degrade the signal more than the adapters do.

                            Comment


                            • Originally posted by peterhr View Post
                              The first simple antenna I made was to
                              strip maybe 80mm of the outer sheath from some co-ax,
                              separate the inner and the outer with the co-ax horizontal pull the inner so it's vertically up, the outer so it's down (after twisting it)
                              chop inner and outer to 66mm long

                              I then mounted it on the end of a gallows made from a 10' bamboo cane and some plant support dowels - so I could stick it higher than I could reach.

                              Peter, you are a very practical minded person.
                              I am really impressed by your ingenuity and practical, problem-solving approach.
                              Last edited by abcd567; 2014-01-13, 19:18.

                              Comment


                              • ....Here is This Week's Top 4 Stubs Chart .....
                                (ALL WITHOUT AMPLIFIER)

                                At Number-4 is : 5 mm spacing, Open-ended stub
                                franklin+impedance-matching-OPEN-stub-5mm.jpg

                                At Number-3 is : 5 mm spacing, Short-circuited stub
                                franklin+impedance-matching-stub-2.jpg

                                At Number-2 is : 10 mm spacing, Open-ended stub
                                franklin+impedance-matching-OPEN-stub-10mm.jpg

                                And at Number-1, the winnwr is : 10 mm spacing, Short-circuited stub
                                franklin+impedance-matching-SHORTED-stub-10mm spacing.jpg
                                Last edited by abcd567; 2014-01-13, 21:30.

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