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3 EASY ANTENNAS FOR BEGINNERS

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  • #91
    The Jpole antenna has a good circular radiation diagram it has also a 0-40° horizontal characteristic that reduces the excessive power from close overflights.

    Currently the antenna is only taped to a window for testing. The final design will be however to have it outdoors placed into a piece of 16mm PVC pipe.

    The other part of the design is to have also the raspberry pi and the receiver outdoors as well, close to the antenna to avoid losses.
    On UHF, every intermediate connector and every meter coax reduce sensitivity.

    The raspberry pi outdoors runs xrdp, which provide a comfortable remote desktop display on a windows client.
    So you just need no cables, a power socket and you are done, the rest works over WiFi.

    Comment


    • #92
      Originally posted by RIN67630 View Post
      The spider or the cantennas are nothing else than a 1/4 λ ground plane with a maximum gain of 1.
      The J antenna is a 5/8 λ which gets ideally 3dB more.

      It has moreover the advantage of being electrically shortcuted and rejects pretty well all low frequencies.
      The construction is very easy, just bend a piece of 2,5mm² copperwire and solder the coax cable.
      The balun can be made of the same coax cable (original cable) which eliminates all connector losses.
      The Raspi is (here together with a sound metering station) is housed waterproof in an IP65 casing
      Here the photograph without cover and mounted for testing in front of a window.
      The next step is to put the J antenna in a piece of 16mm PVC pipe and to put everything on a terrace close to the roof.
      http://www.cjoint.com/doc/16_03/FCvr...321-175050.jpg
      Seen the photo.Your setup is very neat & crafty. Housing the equipment inside a weather proof box has made your equipment suitable for outdoor installation. The J-Pole also looks elegant and neatly built.

      It will be nice if you can post some drawing for J-Pole, giving necessary dimensions, so that other forum members can also make it. Giving details of coax balun will be additional advantage for all.

      By the way, what is the purpose of having a sound monitor in the box holding your equipment?

      Comment


      • #93
        @RIN67630:
        You are right about gain & radiation curves of 5/8 λ J-Pole, and 1/4 λ groundplane, except that you missed one thing: the 1/4 λ tall vertical cylidrical wall of Cantenna acts as a decoupling sleeve also, and hence improves performance without need of an additional balun.

        I dont disagree with the conclusions you have drawn from theory, but often the trial runs of antennas defeat the theory. There is no harm in making an easy to fabricate Cantenna, and put on trial run, and compare with your J-Pole. This comparison can be done even indoors. You can then post comparison results in the forum. Your comparison test results will act as guide to other forum members in choosing which antenna to make.

        Comment


        • #94
          Originally posted by abcd567 View Post
          It will be nice if you can post some drawing for J-Pole, giving necessary dimensions...
          Here ist the detail view of the balun und the coax connection:
          http://www.cjoint.com/doc/16_03/FCwi...322-090136.jpg
          The dimensions are given here:
          http://www.hamuniverse.com/jpole.html

          Originally posted by abcd567 View Post
          By the way, what is the purpose of having a sound monitor in the box holding your equipment?
          I am monitoring aircraft noise. The final purpose is to get a report on all overflights with: altitude, speed, aircraft type and the corresponding sound pressure level.
          Last edited by RIN67630; 2016-03-22, 10:04.

          Comment


          • #95
            Originally posted by RIN67630 View Post
            Here ist the detail view of the balun und the coax connection:
            http://www.cjoint.com/doc/16_03/FCwi...322-090136.jpg
            The dimensions are given here:
            http://www.hamuniverse.com/jpole.html
            Danke schöen. I will give it a try this weekend.
            Last edited by abcd567; 2016-03-22, 10:21.

            Comment


            • #96
              Originally posted by abcd567 View Post
              ... There is no harm in making an easy to fabricate Cantenna, and put on trial run, and compare with your J-Pole. This comparison can be done even indoors. You can then post comparison results in the forum. Your comparison test results will act as guide to other forum members in choosing which antenna to make...
              My purpose is not to get DX results, but to be able to "see" low flying aircrafts beyond a hill behind my house.
              The J-pole performed -compared with the T-dipole that i have previously built- much better.

              My other concern was that I have a police station in the vicinity which powerfull 350MHz sender easily overtuned the reciever. The Jpole rejects these unwanted frequencies much better than 1/4λ antennas.

              Indeed -if you can solder- that is the easiest way to get better results:
              Nothing to to buy extra: it uses the delivered coax cable, all you need is a piece of plain copper wire and two cable binders.
              The "balun" is really easy to achieve.
              Indoors, on a windows it is quite discrete. If you place the Raspi close to it you can have a neat installation, just behind the curtains.

              Outdoors, the antenna is small enough to be placed in a PVC pipe.
              Placing the Raspi in an IP67 box is not that difficult either.
              And you have got no cables through your house. Something that your spouse will not hate ;-)

              Regards
              Last edited by RIN67630; 2016-03-22, 12:23.

              Comment


              • #97
                I recently acquired a similar antenna from ebay, I am connecting with a bnc to f connector into my dongle giving me great coverage.

                I also purchased a filter if I connected that will it help improve my signal?

                2016-03-22_12-00-29.jpg
                2016-03-22_12-04-04.jpg

                Comment


                • #98
                  So the box is on the roof:

                  http://www.cjoint.com/doc/16_03/FCwo...322-150736.jpg

                  Obviously + 250% more planes than indoors, although it was not my aim to get DX range.
                  I get the traffic from Amsterdam to Frankfurt despite the fact that I am in a valley.


                  The whole thing is mounted on a heavy stone plate, so I had not to drill in the roof.

                  Comment


                  • #99
                    Originally posted by RIN67630 View Post
                    The spider or the cantennas are nothing else than a 1/4 λ ground plane with a maximum gain of 1.
                    The J antenna is a 5/8 λ which gets ideally 3dB more.

                    It has moreover the advantage of being electrically shortcuted and rejects pretty well all low frequencies.
                    The construction is very easy, just bend a piece of 2,5mm² copperwire and solder the coax cable.
                    The balun can be made of the same coax cable (original cable) which eliminates all connector losses.
                    The Raspi is (here together with a sound metering station) is housed waterproof in an IP65 casing
                    Here the photograph without cover and mounted for testing in front of a window.
                    The next step is to put the J antenna in a piece of 16mm PVC pipe and to put everything on a terrace close to the roof.
                    http://www.cjoint.com/doc/16_03/FCvr...321-175050.jpg
                    As a ham, i agree with you. Jpole is one best antenna for vhf band and up.


                    Sent from my iPad using Tapatalk

                    Comment


                    • Originally posted by andrewh_85 View Post
                      I recently acquired a similar antenna from ebay, I am connecting with a bnc to f connector into my dongle giving me great coverage.

                      I also purchased a filter if I connected that will it help improve my signal?

                      [ATTACH=CONFIG]7214[/ATTACH]
                      [ATTACH=CONFIG]7215[/ATTACH]
                      What you picture is NOT a filter, it is an in-line amplifier, it will not do anything without a bias-t power injector and psu, and possibly a DC blocker depending on the antenna type you connect it to, if you just connect it as it is all it will do is block the signal and you will not receive any aircraft!
                      With the correct setup then it might help if your signals are low, see elsewhere in the very long antenna thread for more details.

                      Additionally I have just looked at the other picture you posted, you will almost certainly need a DC blocker with that antenna as it is probably a J-pole type.
                      Last edited by F-EGLF1; 2016-03-22, 19:01.
                      FR24 F-EGLF1, Blitzortung station 878, OGN Aldersht2, PilotAware PWAldersht, PlanePlotter M7.

                      Comment


                      • Originally posted by RIN67630 View Post
                        So the box is on the roof:

                        http://www.cjoint.com/doc/16_03/FCwo...322-150736.jpg

                        Obviously + 250% more planes than indoors, although it was not my aim to get DX range.
                        I get the traffic from Amsterdam to Frankfurt despite the fact that I am in a valley.


                        The whole thing is mounted on a heavy stone plate, so I had not to drill in the roof.
                        Seen the photo of your roof top installation. Great built, neat, elegant & crafty. Congratulations.

                        Although you are not interested in DX, it s fun to find out what maximum range you can get from your location inside a valley.

                        Please see this thread:
                        What is the Maximum Range I can Get?

                        Comment


                        • Originally posted by skyspotter View Post
                          As a ham, i agree with you. Jpole is one best antenna for vhf band and up.
                          J-Pole is a clever modification of an already established antenna, the "full wave dipole with impedance matching stub".

                          First, the lower limb of dipole was removed to make it a monopole. Next step was a clever thing: bend down the phasing stub to make it inline with monopole instead of being perpendicular to it . This resulted in J-Pole to be an end-fed antenna, and made it's installation much easier than center-fed dipoles.

                          The trikiest thing in J-pole, Slim Jim and Franklin dipole with matching stub is the accurate placement of cable tap off on the stub. At Ghz frequencies, few mm away from optimum point, and the antenna transforms from "very good" to "poor". At lower frequencies, where dimensions are big, it is much easier to accurately place cable tap-off.

                          Comment


                          • Originally posted by F-EGLF1 View Post
                            What you picture is NOT a filter, it is an in-line amplifier, it will not do anything without a bias-t power injector and psu, and possibly a DC blocker depending on the antenna type you connect it to, if you just connect it as it is all it will do is block the signal and you will not receive any aircraft!
                            With the correct setup then it might help if your signals are low, see elsewhere in the very long antenna thread for more details.

                            Additionally I have just looked at the other picture you posted, you will almost certainly need a DC blocker with that antenna as it is probably a J-pole type.
                            Cheers for the help. At the minute I just have it connected straight to the dongle. Is the below link the correct type of dc blocker. Would I just connect that between the antenna and dongle?

                            image.jpg

                            Comment


                            • Originally posted by andrewh_85 View Post
                              I recently acquired a similar antenna from ebay, I am connecting with a bnc to f connector into my dongle giving me great coverage.

                              I also purchased a filter if I connected that will it help improve my signal?

                              [ATTACH=CONFIG]7214[/ATTACH]
                              [ATTACH=CONFIG]7215[/ATTACH]
                              Originally posted by F-EGLF1 View Post
                              What you picture is NOT a filter, it is an in-line amplifier, it will not do anything without a bias-t power injector and psu, and possibly a DC blocker depending on the antenna type you connect it to, if you just connect it as it is all it will do is block the signal and you will not receive any aircraft!
                              With the correct setup then it might help if your signals are low, see elsewhere in the very long antenna thread for more details.

                              Additionally I have just looked at the other picture you posted, you will almost certainly need a DC blocker with that antenna as it is probably a J-pole type.
                              Since the antenna image does not say it is a jpole, there may or may not be a dc short. The best way is to check for short using multimeter. However there is no harm in installing a dc voltage blocker as a precaution.

                              Comment


                              • Originally posted by abcd567 View Post
                                Since the antenna image does not say it is a jpole, there may or may not be a dc short. The best way is to check for short using multimeter. However there is no harm in installing a dc voltage blocker as a precaution.

                                That antenna, is surely shorted. Omni directional antennas like this has a coil tap making it resonant to a frequency as advertised. It uses a capacitor to tap to the coil.


                                Sent from my iPad using Tapatalk

                                Comment

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