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  • Originally posted by gregy View Post
    hello ABCD567
    reference your post #1391

    can you pls confirm if this design is for 50 or 75 ohm?
    from the SWR plot it would suggest that its 75ohm

    Q: do the dimensions as shown change for 50 ohm? (im using 50ohm coax cable before/after 50ohm masthead LNA)
    If dimensions are different - is it possible to indicate these?

    thanks
    Yes, the design is based on 75 ohm system, but using it on 50 ohm system will not cause any big loss in performance.

    I did not try how this design matches with 50 ohm. Maybe just moving the cable tap few mm will tune it for 50 ohms system.

    Give me some time to go through the simulation /modelling to workout the 50 ohms dimensions, if different.

    Comment


    • Originally posted by YWYY View Post
      Yes thanks for giving me that file. Its very useful, I am learning to use it - slowly. I figured that to use FAR FIELD. When I run it I get errors found - run segment check. It still works ok , but maybe my settings are different to yours.
      Mike
      It always give me "errors found-run segments check", but the results are ok so i simply ignore it. I use default settings & free space.

      Comment


      • Originally posted by gregy View Post
        hello ABCD567
        reference your post #1391

        can you pls confirm if this design is for 50 or 75 ohm?
        from the SWR plot it would suggest that its 75ohm

        Q: do the dimensions as shown change for 50 ohm? (im using 50ohm coax cable before/after 50ohm masthead LNA)
        If dimensions are different - is it possible to indicate these?

        thanks
        Originally posted by abcd567 View Post
        Yes, the design is based on 75 ohm system, but using it on 50 ohm system will not cause any big loss in performance.

        I did not try how this design matches with 50 ohm. Maybe just moving the cable tap few mm will tune it for 50 ohms system.

        Give me some time to go through the simulation /modelling to workout the 50 ohms dimensions, if different.
        I have done simulation for 50 ohm.
        The Gain & Cable Tap position are same as for 75 ohm.
        SWR is a little bit higher i,e for 75 ohm it was 1.52, and for 50 ohm it is 2.08.

        SWR can be reduced if the Matching stub gap is reduced, but it is difficult to achieve narrower gaps and sharper bends with a thick wire of 3mm dia.

        Please see the simulation Results for 50 Ohm system:

        franklin-50 ohm-4E-3mm wire-6mm gap-round bend-gain-pattern.png
        Last edited by abcd567; 2014-08-31, 03:19.

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        • NEW ANTENNA - THE COILED DIPOLE


          STEP 1 - MODELLING & SIMULATION




          STEP 2 - CONSTRUCTION




          STEP 3 - TRIAL RUN
          The the Camera Flash has created shadows of coils on the blinds, making coils look like double helix, with much more than actual number of turns.
          Last edited by abcd567; 2014-09-02, 17:09.

          Comment


          • .
            The VRS Coverage of the Coiled Dipole (see above post).

            12 hrs trial run Without Amplifier. Length of Coax Cable between antenna & receiver = 12 ft (3.5 meters).

            Range rings are 50 nautical miles apart



            Last edited by abcd567; 2014-09-02, 21:58.

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            • ANOTHER EXPERIMENT - CANTENNA WITH COILED WHIP

              image 1 of 2 - Photo




              image 2 of 2 - Coverage 12 hrs run
              Without Amplifier, 12 ft/3.5 meter coax cable between antenna & receiver

              Range Rings are 50 nautical miles apart.

              Comment


              • and now the amplified coiled dipole?

                Comment


                • Originally posted by peterhr View Post
                  and now the amplified coiled dipole?
                  Ok, will do trial run this weekend: coiled dipole+ Amplifier +50 ft/15m rg6 coax between antenna & receiver..

                  Have done trimming of 1/2 wavelength dipole.

                  The dipole limbs were trimmed in steps of 3mm, then put to trial run after each trim. Started from 69mm, went upto 60mm. As the length was reduced, range reduced, the number of far away planes reduced, and number of nearby planes increased.
                  Last edited by abcd567; 2014-09-03, 20:33.

                  Comment


                  • Can anyone guide me which is an INEXPENSIVE equipment to measure SWR/reflected power/impedance of an antenna or transmission line? Any idea about cost of such equipment? I have a very limited budget for my hobby.

                    Comment


                    • Thank you very much for providing very useful information.

                      Comment


                      • same ebay shop has one of these,

                        http://www.ebay.com/itm/3MHz-1200MHz...item35dba96a53

                        you will need this to do your tuning. You can get directional couplers from many places

                        watch this video (the first i found) you could in theory use the DVB-T dongle as the spectrum analyser this would then allow you to tune aerials.
                        https://www.youtube.com/watch?v=zVeAGy0LQow

                        Food for thought for doing this at home myself.
                        Last edited by SpaxmoidJAm; 2014-09-04, 20:52.
                        T-EGLF8

                        Comment


                        • Originally posted by SpaxmoidJAm View Post
                          same ebay shop has one of these,

                          http://www.ebay.com/itm/3MHz-1200MHz...item35dba96a53

                          you will need this to do your tuning. You can get directional couplers from many places

                          https://www.youtube.com/watch?v=zVeAGy0LQow

                          watch this video (the first i found) you could in theory use the DVB-T dongle as the spectrum analyser this would then allow you to tune aerials.

                          Food for thought for doing this at home myself.
                          Thank you very much for sharing a very useful information.
                          Last edited by abcd567; 2014-09-04, 20:57.

                          Comment


                          • it might need a lot playing to get it to work mind but that's half the fun.

                            www.mini-circuits.com have a lot of RF stuff not the cheapest but they are good. I will look tomorrow to see which coupler i brought, they have a bewildering amount of stuff.
                            T-EGLF8

                            Comment


                            • DIPOLE LENGTH vs. RADIATION PATTERN & GAIN



                              As shown by the above animation, the full wavelength dipole has a combination of high gain and a horizontal pattern which is most favourable for ADS-B, but has the disadvantage of very high impedance, which requires impedance matching arrangement (stub, coil etc)

                              The 1.25 wavelength dipole is also similar to full wavelength, and has slightly better directivity in horizontal direction, & lower impedance than fullwave, hence easier to match the impedance. It Is very popular as 5/8 wavelength whip with ground plane (the 1.25 wavelength dipole is two limbs of 5/8 = 2 x 5/8 = 10/8 =1.25).

                              The 5/8 wavelength whip with maching coil at bottom is a popular whip for mounting on vehicles, where metallic body of the vehicle serves as ground plane.



                              Last edited by abcd567; 2014-09-05, 11:56.

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