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  • @Trigger
    @HermanZA

    Yesterday I ran simulation of franklin (with 3 mm conductor 6mm gap) on 4nec2 software, and it gave very erratic results. I then ran simulation on MMANA-GAL software, it also gave very erratic results. It seemed these software are not capable to properly handle thick wire.

    Today when I ran simulation again (for 3mm wire with 6mm gap between wires) on 4nec2, it showed good results !!!!!! It gave optimum tap position at 47mm from open end (or 69-47=22mm from shorted end). I don't know if this is again a misbehavior of software or is it genuine. Best way left now is to build & test.


    Edit: simulation results deleted due to error in wire data (wire 10). See corrected results in new post below
    Last edited by abcd567; 2014-07-29, 16:10.

    Comment


    • Simulation Results Franklin 4-element by 4nec2 software gives Gain =6.19 dBi & SWR=1.17:

      Wire dia = 3mm
      Gap between stub wires =6 mm (center-to-center distance between stub wires = 1.5 mm + 6 mm + 1.5 mm = 9 mm)
      Optimum cable tap position = 45 mm from open end (or 69 mm -45 mm = 24 mm from shorted end)

      franklin-4 element-3mm wire 6mm gap - pattern gain swr-R1.png . franklin-4 element-3mm wire 6mm gap - Sweep for Tap position-R1.png . franklin-4 element-3mm wire 6mm gap - input data-R1.png
      Last edited by abcd567; 2014-07-29, 16:49.

      Comment


      • Same wire data as above, simulated in software MMANA-GAL, gives Gain = 7.35 dBi, & very high SWR = 133 !!!!!!

        Which software to trust????

        Wire dia = 3mm
        Gap between stub wires =6 mm (center-to-center distance between stub wires = 1.5 mm + 6 mm + 1.5 mm = 9 mm)
        Optimum cable tap position = 45 mm from open end (or 69 mm -45 mm = 24 mm from shorted end)


        franklin 4element 3mm wire 6mm gap layout - mmna-gal.png. franklin 4element 3mm wire 6mm gap pattern mmna-gal.png . franklin 4element 3mm wire 6mm gap wire data mmna-gal.png
        Last edited by abcd567; 2014-07-29, 17:57.

        Comment


        • The guys at http://forum.flightradar24.com/threa...-Over-The-IRAN would like a solution ... an easy to build reliable antenna, that doesn't need esoteric bits.

          Comment


          • Another Simple Antenna:
            http://qsl.net/py4zbz/adsb.htm#e

            One more here:
            http://www.lesaunier.com/htm/franklin1_eng.htm

            cable tap arrangement: http://www.lesaunier.com/images/radi...franklin_8.jpg
            Last edited by abcd567; 2014-07-30, 05:57.

            Comment


            • Another, similar to one above
              http://adsbradar.ru/antenna-franklin-1090mhz
              Last edited by abcd567; 2014-07-30, 16:15.

              Comment


              • What about a strait forward dipole, it doesn't get any easier than that.

                With collinear aerial yes you do need to be exact with your measurements and know your exact velocity factor to do that. How ever of all the ones i have made and haven't been exact and just thrown them together they still work quite well and generally better than you think. Certainly for the cost of the coax worth ago.
                Last edited by SpaxmoidJAm; 2014-07-30, 18:15.
                T-EGLF8

                Comment


                • Originally posted by SpaxmoidJAm View Post
                  What about a strait forward… dipole, it doesn't get any easier than that.......
                  My very first antenna was a 1/2 wavelength Dipole.
                  Gain 2.2 dBi, impedance=75 ohms, hence SWR=1 : )

                  Because of it's low gain (2.2 dBi) & long run of coax (50 feet/15m as antenna & desktop are in different rooms of my apartment), I had to add an inline amplifier (13 - 18 dB).

                  Last edited by abcd567; 2014-07-30, 23:57.

                  Comment


                  • Thank you all for a very interesting thread!

                    I would like to add some quotes from some of the material I've been reading recently:

                    LENGTH AND PHASING.—Although the 1/2 wavelength is the basis for the collinear element,
                    you will find that greater lengths are often used. Effective arrays of this type have been constructed in
                    which the elements are 0.7 and even 0.8 wavelength long. This type of array provides efficient operation
                    at more than one frequency or over a wider frequency range. Whatever length is decided upon, all of the
                    elements in a particular array should closely adhere to that length. If elements of different lengths are
                    combined, current phasing and distribution are changed, throwing the system out of balance and seriously
                    affecting the radiation pattern.

                    SPACING.—The lower relative efficiency of collinear arrays of many elements, compared with
                    other multi-element arrays, relates directly to spacing and mutual impedance effects. Mutual impedance is
                    an important factor to be considered when any two elements are parallel and are spaced so that
                    considerable coupling is between them. There is very little mutual impedance between collinear sections.
                    Where impedance does exist, it is caused by the coupling between the ends of adjacent elements. Placing
                    the ends of elements close together is frequently necessary because of construction problems, especially
                    where long lengths of wire are involved.

                    The effects of spacing and the advantages of proper spacing can be demonstrated by some practical
                    examples. A collinear array consisting of two half-wave elements with 1/4-wavelength spacing between
                    centers has a gain of 1.8 dB. If the ends of these same dipoles are separated so that the distance from
                    center to center is 3/4 wavelengths and they are driven from the same source, the gain increases to
                    approximately 2.9 dB.

                    A three-dipole array with negligible spacing between elements gives a gain of 3.3 dB. In other
                    words, when two elements are used with wider spacing, the gain obtained is approximately equal to the
                    gain obtainable from three elements with close spacing. The spacing of this array permits simpler
                    construction, since only two dipoles are used. It also allows the antenna to occupy less space.
                    Construction problems usually dictate small-array spacing.
                    The above from: http://www.navymars.org/national/tra.../14182_ch4.pdf
                    More on element spacing at: http://www.w8ji.com/stacking_broadside_collinear.htm

                    It seems most people agree that a "free-space" tuned CoCo will be detuned by placing it inside a plastic tube. However, if this detuning makes the antenna "appear" too long, it might not be disastrous, because longer-than-λ/2 elements are not necessarily that bad? And with a "too long" antenna, the apparent element spacing would also be longer, which might actually be beneficial. All in all, to PVC or not to PVC might be a moot point?

                    Cheers,

                    A lurker

                    Comment


                    • A reasonable design target is 5DB antenna gain and an antenna amplifier like the one shown. The amplifier does two things, one is gives some compensation for impedence mismatching (presuming the amplifier has a fairly high input and low output impedance) and makes it possible to use a downfeed of somewhat unknown quality. I do 'like' the franklin designs (not that I have built one) because of their simplicity and repeatability ... but they would need DC voltage decoupling between the amplifier and antenna.

                      Comment


                      • Originally posted by peterhr View Post
                        A reasonable design target is 5DB antenna gain and an antenna amplifier like the one shown. The amplifier does two things, one is gives some compensation for impedence mismatching (presuming the amplifier has a fairly high input and low output impedance) and makes it possible to use a downfeed of somewhat unknown quality. I do 'like' the franklin designs (not that I have built one) because of their simplicity and repeatability ... but they would need DC voltage decoupling between the amplifier and antenna.
                        You have yourself solved the DC Blocking problem in an easy & cheap (£3.99) way in your post # 1282 on page 129

                        http://www.ebay.co.uk/itm/171258939281

                        DC Block-R.jpg

                        2 X F-THROUGH CONNECTOR - DC BLOCK

                        Comment


                        • @Trigger
                          @HermanZA


                          Here is your franklin with 3mm dia wire, 6mm gap by wrapping wire around 6mm drill bit
                          Good news Gain=6.86 SWR=1.52

                          NOTE: The impedance matching stub (middle one) is slightly bigger than phasing stubs (upper & lower ones)

                          Reason - to meet the following two conditions:

                          (1) Phasing stub:
                          Total wire length (two horizontal parts + round part) should be 1/2 wavelength = 138mm

                          (2) Matching stub:
                          Each horizontal length should be 1/4 wavelength = 69 mm.
                          Hence total wire length of horizontal parts alone should be = 2 x 69 = 138 mm.
                          The total wire length of matching stub (including round part) should be 138 mm +length of round part.
                          Length of round part = pi x round part diameter/2 = 3.14 x (1.5+6+1.5)/2 =14 mm.
                          Hence total wire length for Matching stub = 138 mm + 14 mm = 152 mm

                          Do not get confused by theory above. Ignore it and simply follow the dimensions given in the sketch I have drawn below, and it is done.

                          franklin 3mm dia wire-6mm gap stub-how-to.jpg . franklin-4E-3mm wire-6mm gap-round bend-gain-pattern.png . franklin-4E-3mm wire-6mm gap-round bend-swr sweep.png . franklin-4E-3mm wire-6mm gap-round bend-input wire data.png
                          Last edited by abcd567; 2014-07-31, 15:25.

                          Comment


                          • Indeedy!
                            I suppose I'll have to add your Franklin design + blocker + amp + downlead + voltage Injector + pigtail to a new 'Cheap antenna for FR24' thread - something I don't really want to 'own' since there are others much more interested in such things than I am. My interest is really in a simple cheap RPI based receiver and it could really do with a excellent simple cheap antenna design to go with it that doesn't require the reader to plough through over a thousand posts to get the info.

                            Comment


                            • Originally posted by peterhr View Post
                              Indeedy!
                              I suppose I'll have to add your Franklin design + blocker + amp + downlead + voltage Injector + pigtail to a new 'Cheap antenna for FR24' thread - something I don't really want to 'own' since there are others much more interested in such things than I am. My interest is really in a simple cheap RPI based receiver and it could really do with a excellent simple cheap antenna design to go with it that doesn't require the reader to plough through over a thousand posts to get the info.
                              Wait till more than one forum members built the latest Franklin (3mm wire dia, 6mm gap), put it on trial run, and report back results.
                              Last edited by abcd567; 2014-07-31, 15:36.

                              Comment


                              • I checked Home Depot and Canadian Tire in my area, they dont have 3mm dia (9AWG) wire. The largest they have is 12AWG (2 mm dia). I will search other stores on this weekend. If I get 3mm dia wire, I will make the Franklin. Uptill now I have been using core of RG6 cable, which is 18AWG (1 mm dia) to make wire antennas. Since my antennas are indoor, no wind, 1 mm dia wire is ok. Due to it being thin, it's bending, cutting & narrow gaps are easy to form.
                                Last edited by abcd567; 2014-07-31, 20:42.

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