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  • ABCD, Thanks for the help and support with this one. The next one (or maybe two) will be easier to make and quicker. But that will only happen when the I drop the pole to the ground for some maintenance and adding these. Height is an issue, as always. I can feel your dispair with multiple CoCo's and no stable result with them.
    Perhaps when next you run that antenna modelling software of yours, you can model this Yagi and see what it gives i.t.o. gain and VSWR and all that.

    Trigger: 3 of them wont help much, as they are effective in about 35-45 degrees (Horizontal and Vertical), but yeah, combining them would be a total disaster in the making, I agree with Rooster, as I have seen ons of those phasing harnesses before . But it would have been great, should it be easy to accomplish.

    I think what we have learnt, is that a directional yagi (to cover an airport perhaps) is within the reach of the average DIY hobbyist. That is what I'll test with the next antenna or two, aim it directly at certain "interesting" areas to see what it picks up. Have a spare dongle or two to help with running these setups.
    Last edited by HermanZA; 2014-11-18, 21:22.

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    • Why not just use four dongles and let software (e.g. ModeSMixer) merge the feeds into a single feed for upload? No loss or phasing issues then.

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      • Eastons,

        I think I'm going to end up with that as a solution. Havent worked with ModeSMixer yet, been a bit afraid to add even more software, but I think the time has come...

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        • Originally posted by HermanZA View Post
          .......Perhaps when next you run that antenna modelling software of yours, you can model this Yagi and see what it gives i.t.o. gain and VSWR and all that.......
          Here it is
          HermanZAs First Yagi.PNG

          Comment


          • Originally posted by eastons View Post
            Why not just use four dongles and let software (e.g. ModeSMixer) merge the feeds into a single feed for upload? No loss or phasing issues then.
            Originally posted by HermanZA View Post
            Eastons,

            I think I'm going to end up with that as a solution. Havent worked with ModeSMixer yet, been a bit afraid to add even more software, but I think the time has come...
            Great! Waiting for results of this experiment.

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            • Thanks for plotting that ABCD! Yours shows even higher gain than the calculator I used for it.

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              • Originally posted by HermanZA View Post
                Thanks for plotting that ABCD! Yours shows even higher gain than the calculator I used for it.
                My results = 14.3 dBi = 14.3- 2.2 dBd = 12.1 dBd

                Your calculator gives 12.1 dB. If "dB" in your results is dBd, then your & my results are same.

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                • Question on this PCB antenna (Link)

                  How do you calculate the VF? Just for my understanding, is it as simple as VF of the PCB material plus 1 (air) divided by 2?

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                  • Originally posted by hikeofyourlife View Post
                    Question on this PCB antenna (Link)

                    How do you calculate the VF? Just for my understanding, is it as simple as VF of the PCB material plus 1 (air) divided by 2?
                    VF = 1/squre root of dielectric constant of insulating material between two conductors.

                    Comment


                    • Originally posted by abcd567 View Post
                      VF = 1/squre root of dielectric constant of insulating material between two conductors.
                      I'm aware of that formula but if the VF of FR4 PCB is 0.46-ish then why are the quarter-wave elements on the antenna only 53 mm? Quarter-wave in air is 68 mm so there must be a combination of air to conductor and FR4 material to conductor

                      Comment


                      • Originally posted by hikeofyourlife View Post
                        I'm aware of that formula but if the VF of FR4 PCB is 0.46-ish then why are the quarter-wave elements on the antenna only 53 mm? Quarter-wave in air is 68 mm so there must be a combination of air to conductor and FR4 material to conductor
                        The electric field of microstrip is partly in air and partly in FR4 board's insulation

                        FR4 board's insulation has a dielectric constant εr of 4 at 1000 Mhz, hence VF of FR4 = 1/square root of 4 = 1/2 = 0.5
                        Air has a dielectric constant εr of 1, hence VF of air = 1/square root of 1 = 1/1 = 1

                        Due to mixed insulation, the dielectric constant εr of microstrip is different from 4, depending on geometry. Consequently the VF is somewhat different from o.5

                        There are several empirical equations in use, the most common is:
                        ε'r = 0.475εr + 0.67

                        Please read this article for formula to calculate VF of microstrip: http://www.ultracad.com/mentor/microstrip propagation.pdf

                        Calculator for ε'r: http://www.microwaves101.com/calcula...rip-calculator

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                        • @ikeofyourlife

                          It seems 1/4 wave has been taken = 53mm as an easy aproximation by averaging VFs of FR4 & Air.
                          Dielectric constant εr of air = 1; VF air = 1/√εr = 1/√1 = 1

                          Dielectric constant εr of FR4 = 4; VF FR4 = 1/√εr = 1/√4 = 1/2 = 0.5

                          The formula you mentioned for VF = (VF of FR4 + VF of air)/2 is simply averaging VFs of FR4 & air, and is not accurate enough. Using this formula gives VF = (0.5+1)/2 = 0.75 and 1/4 wave element length = 0.75 x 275/4 = 51.6 mm.

                          According to more accurate empirical formula, Dielectric constant (corrected for mixed enviroment) = ε'r = 0.475εr + 0.67

                          For FR4, the dielectric constan εr = 4
                          Hence ε'r = 0.475x4 + 0.67 = 2.57
                          The corrected VF = 1/√2.57 = 0.624
                          The 1/4 wave element length = 0.624 x 275/4 = 43 mm

                          A more accurate value, taking into consideration the dimensions of microstrip is by calculator http://www.microwaves101.com/calcula...rip-calculator
                          Last edited by abcd567; 2014-11-22, 08:09.

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                          • Originally posted by abcd567 View Post
                            NEXT PLANNED EXPERIMENT.. maybe next week end.

                            Step (1): Build 8-Element CoCo made of RG6 coax, FPE insulation VF=0.83 Element Length=114 mm
                            Step (2): Put above CoCo on 24 hrs trial run. Repeat the 24 hrs trial run on another day(s).

                            Step (3): Same CoCo as above, but twin-lead impedance matching added between feed line & bottom element. Adjust length of twin-lead for best results.
                            Step (4): Put CoCo in step (3) on 24 hrs trial run. Repeat the 24 hrs trial run on another day(s).

                            Starting point: Computer simulation results from 4nec2 software:
                            (1) 8-Element CoCo without impedance match: SWR= 3.4, Gain = 8.5 dBi Antenna Impedance = 81.9-j102 ohms
                            (2) 8-Element CoCo with Twin-Lead impedance match: Twin-Lead Length 21 mm (adjust few mm for best results) , SWR= 1.02, Gain = 7.9 dBi

                            Twin-Lead Length for 8-Element CoCo by Smith Chart = 27.5 mm approximately (adjust few mm for best results)
                            [ATTACH=CONFIG]5025[/ATTACH]
                            Hi ab cd, I've built a new 8 element coco with the twin-lead impedance matching and the results are promising. Pretty close to my Franklin. The weather here is low cloud/rain/mist so not ideal. The VF of the coax I'm using is around 0.66 giving an element length of 91mm. Can you calculate the optimum length of the twin-lead for me? I'm currently using 35mm. Thanks, Dave
                            T-EGUB1

                            Comment


                            • Originally posted by trigger View Post
                              Hi ab cd, I've built a new 8 element coco with the twin-lead impedance matching and the results are promising. Pretty close to my Franklin. The weather here is low cloud/rain/mist so not ideal. The VF of the coax I'm using is around 0.66 giving an element length of 91mm. Can you calculate the optimum length of the twin-lead for me? I'm currently using 35mm. Thanks, Dave
                              What type of coax (e.g. RG58, RG6, LMR400 etc) you used for making the coco? To calculate length of twin-lead, I need antenna impedance. To get antenna impedance, I need to run simulation. To run simulation, I need diameter of central wire: bare and with core insulation. For example, RG6 has dia of bare conductor = 1 mm, dia over core insulation = 4.8 mm

                              Weather condition here are severely fluctuating, causing max range to jump to abnormally high on some days, and abnormally low on some other days.

                              Comment


                              • Hi ab cd,
                                I don't know what the coax is as it only has sat 100 written on it so possibly RG6? The OD of the cable is 6mm, the OD of the core is 1mm and the OD of the insulation is 4mm. I know the insulation is polyethylene as I had it checked by one of my chemist friends.

                                Back to back comparisons with my 6 element Franklin and this 8 element CoCo without an amplifer give an identical range.
                                I did notice that the CoCo had a lower frame count for almost identical conditions. I simply unplugged the CoCo and plugged in the Franklin and the frame count dropped from 1700 to 1500. The plane count on RTL1090 and PlanePlotter were the same a couple after swapping the antennas.

                                Thanks
                                Last edited by trigger; 2014-11-26, 19:51. Reason: typo
                                T-EGUB1

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