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  • Originally posted by trigger View Post
    ........Hi ab cd, yes I had noticed it . Looking forward to some results.
    I am experiencing a contradiction in results I get by maths, by simulation, and by trial run of prototype.

    Results of maths & simulations agree reasonably close, but when i run prototype, results are much poorer. I dont know why. This happens to Franklins, 5/8, etc.

    There is another strange phenomenon with pepsi-can sleeved dipole. Without amp & connected directly by short piece of cable, it gives better results compared to franklin connected to same setup. With amp & long cable, franklin gives better results than pepsi-can sleeved dipole connected to same setup. Very strange.
    Last edited by abcd567; 2014-08-08, 23:37.

    Comment


    • I am thinking loud about problem presented in my last post above.........

      The tiny 1/2 wavelength dipole & pepsi-can sleeve dipole (which is also a 1/2 wavelength dipole) have an inherent impedance of 75 ohms, if both limbs are cut exactly 1/4 wavelength (69mm). This is easy to accurately achieve. Hence the prototype built by DIY, will have SWR very close to 1.

      In the Franklin & 5/8 coil tuned antennas, the impedance is brought down to 75 ohms by stubs & coils. These are very sensative to accuracy, and a DIY built prototype will rarely have SWR close to designed SWR.

      As a result of above, the1/2 dipoles perform better than franklin & 5/8 coil tuned antennas when used without Amplifier.

      When used with Amplifier, the low SWR is compensated by the Amplifier, hence the stub & coil tuned antennas, which have gain of order of 6 dBi or mre, give better performance than 1/2 wavelength dipoles which have gain of order of 2.2 dBi.

      Comment


      • Hi ab cd,

        You said in a post #1438 above
        "Congratulations you got good results for wrapped stub franklin. Is wrapping dia 22mm?
        Later addition:
        (1) The "kite" photo shows the wrapping is not a complete circle, but about 3/4 circle (270 degrees) so dia should be about 22 x 4/3 =29mm."

        You are, of course, correct. I tweaked the antenna whilst it was at ground level. It started as 22mm. I had the rate graph running in adsbScope and opened/closed the stubs to get the best rate. I also squeezed/opened the stubs a bit. Not very scientific but it seemed to work for me.

        I'll measure the dimensions of the antenna as it is and post what I've currently got.
        Last edited by trigger; 2014-08-09, 07:18. Reason: spelling
        T-EGUB1

        Comment


        • Here are results of my 3 antennas WITHOUT AMPLIFIER, and short (12 feet) Coax from antenna to Receiver.
          As you can see, the Franklin & 5/8 wavelength Coil-Tuned are much inferior to Sleeved dipole when run WITHOUT AMPLIFIER.

          This shows that:
          (1) Half-wave Dipole is inherently tuned with SWR=1 if its two legs are cut at 69mm. This is very easy for any DIY hobbyist.
          (2) Franklin & coil tuned (and coco also) require tuning which depends on dimensions & alignments. Little errors caused by DIY hobbyist throw them far away from optimum. These can be best made accurately only in Factory environment with all jigs, tools, templates & sophisticated test equipment.


          Half wave Sleeved Dipole (Pepsi-can)
          pepsi can halfwave dipole in radome-NO AMPLIFIER short (12 ft) Coax.jpg

          5/8 wavelength dipole with tuning/matching coils
          5by8wavelength+tuning coil-NO AMPLIFIER short (12 ft) Coax.jpg

          4-element Franklin with Matching stub.
          4-element franklin- NO AMPLIFIER short (12 ft) Coax.jpg
          Last edited by abcd567; 2014-08-11, 01:42.

          Comment


          • Here comes sleeved PEPSI-CAN dipole in an eclosure - enjoy, make it very easily & install it outdoors.
            (add amplifier if Coax is long)

            The Antenna




            The Test Setup, WITHOUT Amplifier & Short (12 ft) length of Coax from Antenna to receiver




            The Coverage (WITHOUT AMPLIFIER)




            HOW TO MAKE

            (1) Dimension Diagram



            (2) Collect the materials & tools



            (2) Cut Pepsi-can to 69mm length, drill a hole in the bottom, fix a F-male-to-Female Solderable Panel type connector, Solder a 69mm whip to center of the connector.



            (3) Drill hole in center of Jar's Lid, fix F-Female to Female connector. Also fix the mounting bracket to the Lid by two small nuts & bolts



            (5) Screw Pepsi-can on the connector in the Jar's Lid.



            (6) Screw-on the Jar on the Lid. Your Antenna is ready.



            Enjoy ...
            Last edited by abcd567; 2014-08-11, 00:14.

            Comment


            • .
              If you have a long run of Coax, and want to add an amplifier to the Pepsi-can Sleeved Dipole, install it inside the enclosure beneath the Pepsi-can, like shown in sketch below (drawing is not to scale - lower part of amplifier may protrude outside the can, depending on make/model):

              Comment


              • I really like the simplicity of this and that the pepsi can provides shelter for the amplifier. Maybe screw the amplifier to a long steel strip to provide something to fix to a mast (see http://www.ebay.com/itm/330844552433)

                I really like the raydome to but I'm not sure that would work well up a mast - it would catch too much wind - I wonder if a plastic soda bottle of the correct size could be found to slip over the can and be attached or glued on

                Would a narrower caffine drink (red bull) can work equally well? - this would fit inside a standard coke bottle holding the can centrally with some polystyrene spacers

                Comment


                • @peterhr: The method I have given is a guideline to physically show that the antenna being small, can be fitted inside a bottle like enclosure & provided with a support structure, as opposed to pipe enclosure for coco & no enclodure for franklin. Now it is left to ingunity of various forum members to find better variants of the enclosure.

                  Yes, I have tried a somewhat smaller diameter can like redbull & 220mL pepsi.

                  The small can, same size as 220mL pepsi (dia 2-1/4 inch = 58mm), showed slightly inferior to standard 330mL pepsi (dia 2-5/8 inch = 66mm) shown in pictures above.

                  When I tried a 3/4 inch (20mm) dia copper water pipe with end cap, results were substantially inferior.

                  From above it appears that the circular bottom of can provides an earth plane, while cylindrical wall of the can provides the lower 1/4 limb of the dipole.
                  Last edited by abcd567; 2014-08-11, 21:20.

                  Comment


                  • I had a can of Red Bull in the fridge this morning so it was "sacrificed" for the good of all antenna builders.

                    Range seems to be about 50nm less than my Franklin but reading the above post I may have to have a beer later this evening.......

                    Red Bull.jpg
                    T-EGUB1

                    Comment


                    • Originally posted by trigger View Post
                      I had a can of Red Bull in the fridge this morning so it was "sacrificed" for the good of all antenna builders.

                      Range seems to be about 50nm less than my Franklin but reading the above post I may have to have a beer later this evening.......

                      [ATTACH=CONFIG]4597[/ATTACH]
                      You are my best comrade... support my experiments by repeating these, helping me to say yes/no to my results. The more number of persons experiment & feed back, the more conclusive & authentic are the results.

                      Tip 1: Cut the can about a cm or two longer than 69 mm, and bent the extra length inwards to achive 69mm. This will make the can's edge non-razor sharp. I have cut my fingers when I made my first can, then developed this technique.

                      Tip 2: make 3 cans: 69mm, 69+5mm, & 69-5mm. Try them one by one, and keep the one which gives best results.

                      Comment


                      • Tip 1: Cut the can about a cm or two longer than 69 mm, and bent the extra length inwards to achive 69mm. This will make the can's edge non-razor sharp. I have cut my fingers when I made my first can, then developed this technique. I did remove the sharp edges with a piece of emery paper but I take your point.

                        Tip 2: make 3 cans: 69mm, 69+5mm, & 69-5mm. Try them one by one, and keep the one which gives best results. Oh no! Not more beer. It is 0% alcohol so I guess that's not too bad.
                        Last edited by trigger; 2014-08-11, 18:40. Reason: added 0%
                        T-EGUB1

                        Comment


                        • @trigger: Oh no! Not more beer. It is 0% alcohol so I guess that's not too bad.
                          Due to curved & rimmed shape of drink can's bottom, the reference point from where to measure down 69mm is somewhat not very precise. Using slightly different lengths will give the best length. This trimming technique is very commonly used by HAMs on wire antennas for 2 meter band and longer.

                          Comment


                          • HERE ARE THE ANTENNAS USED IN LAST WEEK's COMPARISION

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                            • I'm a few kilometers from RAF Benson and my Red Bull quarter wave antenna is seeing a lot more aircraft on the ground. They normally disappear at 200 - 300 feet. As far as long distance goes it is definitely down by about 50nm on my coiled Franklin.

                              Is the reason that aluminium cans are recommended to avoid long term problems with rust? I have a Baked Bean can that I'll mangle this afternoon.
                              T-EGUB1

                              Comment


                              • Originally posted by trigger View Post
                                I'm a few kilometers from RAF Benson and my Red Bull quarter wave antenna is seeing a lot more aircraft on the ground. They normally disappear at 200 - 300 feet. As far as long distance goes it is definitely down by about 50nm on my coiled Franklin.

                                Is the reason that aluminium cans are recommended to avoid long term problems with rust? I have a Baked Bean can that I'll mangle this afternoon.
                                Paraps you need two rigs - none for local and one for distance.

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