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  • Originally posted by trigger View Post
    I volunteer !!

    I made an 8 element coco today with 124mm segments. Results are not good, less than 50nm. However, I don't know what type of coax I have. It is stamped sat100 CE F.B.E. Neither the core or braid are magnetic. From previous experiments I think the coax is PTFE so I'll make another two at 109mm and 116mm.

    I'll be back in a couple of days.
    Sat100 seems to be a brand name used in the UK. Satellite systems use Rg6 so it has to be that.
    www.ADS-B.ca

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    • Just curious, I was thinking about making a franklin out of 3/16" copper brake hose - when abcd567 ran it through his calculations it was shown that the tube diameter was too great to make an effective antenna.

      WE have had people on here making antennas out of varuios co-axial from unknown to LMR400 with varying degrees of success. I'm just wondering to what the external diameter of the shield on the co-ax has on the antenna performance - could it be that a nice fat lo-loss downlead is poor material for an antenna and something that is thinner (but of good qualirt so it has a known V) actually works better in this role.

      Comment


      • Originally posted by tvengineer View Post
        Sure.. but I don't know how to draw in ascii :-)
        I used an online jpole calculator..
        Made it out of a single lenght of wire....

        Long side is 198mm ... bottom of the "U" is 6mm .. short side is 64mm..
        Coax shield is soldlered to the short side, center conductor to the long side.. both soldered 6mm up from the bottom "U".

        One thing that is so nice about playing with these antenna is that at 1090 mhz they are so small :-)
        My "mast" is a chopstick that I have taped to an electrical box on the roof :-)

        Edit to add a photo....
        [ATTACH=CONFIG]4448[/ATTACH]
        Here are your JPole's Computer Simulation results:


        Simulation Output - Gain, SWR, Pattern
        tvengineers JPole - simulation output2.png


        Simulation Input - Geometry
        tvengineers JPole - simulation input.png


        .
        Last edited by abcd567; 2014-07-25, 08:29.

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        • Now you have me worried with my idea of building an antenna out of copper piping.... although lots of surface area to "catch" a signal, nice conductive copper.... it might be too large area to be effective.

          Comment


          • Originally posted by peterhr View Post
            Just curious, I was thinking about making a franklin out of 3/16" copper brake hose - when abcd567 ran it through his calculations it was shown that the tube diameter was too great to make an effective antenna.

            WE have had people on here making antennas out of varuios co-axial from unknown to LMR400 with varying degrees of success. I'm just wondering to what the external diameter of the shield on the co-ax has on the antenna performance - could it be that a nice fat lo-loss downlead is poor material for an antenna and something that is thinner (but of good qualirt so it has a known V) actually works better in this role.
            Originally posted by HermanZA View Post
            Now you have me worried with my idea of building an antenna out of copper piping.... although lots of surface area to "catch" a signal, nice conductive copper.... it might be too large area to be effective.
            The Dark Art of CoCo making...sigh

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            • Ya know, just thinking about it - we always worry about how 'long' the element needs to be ... but if it's fat then do you need to take into account that the signal can also travel - sort of - diagonally ... and that would de-tune it.

              Also adding lots of elements sound great - but if you do have a length / tuning error - does that just exacerbate the error? - that's part of the reason that I was asking about the franklin on a ground plane.

              something like that, use a cheap inverted omelette pan for the ground plane (take the handle off). Put a satellite amplifier on the underside of the pan (the pan would protect the amplifier from most of the weather - and as a 'machined item' would look professional, the amplifier would negate most impedance matching issues). That almost gets us back to something like this antenna - but with an amplifier

              Comment


              • Originally posted by peterhr View Post
                Ya know, just thinking about it - we always worry about how 'long' the element needs to be ... but if it's fat then do you need to take into account that the signal can also travel - sort of - diagonally ... and that would de-tune it.

                Also adding lots of elements sound great - but if you do have a length / tuning error - does that just exacerbate the error? - that's part of the reason that I was asking about the franklin on a ground plane.

                something like that, use a cheap inverted omelette pan for the ground plane (take the handle off). Put a satellite amplifier on the underside of the pan (the pan would protect the amplifier from most of the weather - and as a 'machined item' would look professional, the amplifier would negate most impedance matching issues). That almost gets us back to something like this antenna - but with an amplifier
                The Franklin has several 69 mm horizontal stubs, which cannot fit inside a pipe. The french antenna fits into a pipe.

                Have you seen my post #1224 for sleeved Dipole using Pepsi-can? It matches your concept of inverted omlette pan.
                Last edited by abcd567; 2014-07-25, 21:11.

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                • Originally posted by abcd567 View Post
                  The Franklin has several 69 mm horizontal stubs, which cannot fit inside a pipe. The french antenna fits into a pipe.
                  I'm not sure which stubs you're on about...

                  The stubs at the base would be replaced by the ground plane

                  The stubs as you go up the antenna (1 1/2 twists in the French antenna) are there as delay lines and can be rolled to a 23mm diameter (or maybe less) to make the antenna more compact.

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                  • Originally posted by abcd567 View Post
                    Here are your JPole's Computer Simulation results:


                    Simulation Output - Gain, SWR, Pattern
                    [ATTACH=CONFIG]4455[/ATTACH]


                    Simulation Input - Geometry
                    [ATTACH=CONFIG]4456[/ATTACH]


                    .


                    Thanks... I was going to ask you if you would run that.
                    I just can't argue with results.. this thing is working very well. It seems that the antenna that came out of the online calculator uses a 3/4 wave long side... I had not seen that in a j pole before... all I know is it is working :-) The numbers that I used see a little bit off though... the wavelength of a 1/4 (short side) is closer to 69mmm than the 64mm that the calculator gave me... what do I know about antennas.. maybe you don't use the free air wavelength.
                    I think i will build a couple more at slightly different dimensions.... but it is going to be hard to tell if there are slight improvements when this antenna is receiving so well out to 200+ Nm... :-)
                    ...........

                    Comment


                    • Originally posted by peterhr View Post
                      I'm not sure which stubs you're on about...

                      The stubs at the base would be replaced by the ground plane

                      The stubs as you go up the antenna (1 1/2 twists in the French antenna) are there as delay lines and can be rolled to a 23mm diameter (or maybe less) to make the antenna more compact.
                      Forum member "trigger" has earlier tried Franklin with rolled stubs, but got poor results. He may give more information on this. the French antenna has phasing coils instead of stubs. I don't know if any forum member has tried the French antenna.

                      Comment


                      • With people using same design & same material, but getting varying results from vey poor to very good, it looks DIY antenna making is "a shot in dark".... : (

                        Comment


                        • Originally posted by abcd567 View Post
                          With people using same design & same material, but getting varying results from vey poor to very good, it looks DIY antenna making is "a shot in dark".... : (

                          I find that making the Colinear ones is very if'y... they are easy to put together, but to get them to work with good solid connections is difficult.
                          One user here made one with semi rigid cable and soldered joints and his results seemed to be good.

                          I think I have found my "best" antenna in the J pole..
                          Here is a plot of one day with the J pole..
                          jpole1.jpg

                          Next I built a Super J... Same J pole with an extra 1/2 wave section on top coupled by a 1/2 tuning stub.

                          photo.jpg

                          So far the Super J is performing at least as well as the regular J pole..
                          I think with my height above ground and obstructions.. this is about all the performance I can achieve..

                          I have already got 50 feed of very low loss coax run up a tower to get above some of the obstructions around me, but I don't want to be climbing up there to test out antenna.
                          So.. I think it will be the Super J that goes up.. once I get it mounted inside a PVC pipe and figure out how to mount it to the tower some time next week.

                          These are quite easy to make. I can whip one up in less than 15 minutes, and they seem to perform really well for me. Don't know how much more we can hope to squeeze out of an omni directional antenna without getting real complicated with multible elements spaced correctly and complex phasing harnesses.

                          For now I am going to let it run the weekend and get a good plot of the coverage of the Super J on the roof before I raise it up into the air.

                          Comment


                          • Originally posted by tvengineer View Post
                            ........I think I have found my "best" antenna in the J pole..
                            Here is a plot of one day with the J pole..
                            [ATTACH=CONFIG]4458[/ATTACH]

                            Next I built a Super J... Same J pole with an extra 1/2 wave section on top coupled by a 1/2 tuning stub.

                            [ATTACH=CONFIG]4459[/ATTACH]

                            So far the Super J is performing at least as well as the regular J pole..
                            I think with my height above ground and obstructions.. this is about all the performance I can achieve.........
                            CONGRTULATIOS for making a very successful and very simple antenna.

                            1)What is the spacing of 3 range rings on your VRS plot?
                            2) what are the dimensions of super-j's upper limb & phasing coil?

                            Comment


                            • Originally posted by abcd567 View Post
                              With people using same design & same material, but getting varying results from vey poor to very good, it looks DIY antenna making is "a shot in dark".... : (
                              This is called " SKILL ".

                              Give a group of people the same ingredients to prepare some pasta - I am sure they will all turn out differently.
                              F-WSSS1 - Cats refused to Pee & Pooh on RadarBox - Running a FR24 Receiver & DVB-T Dongle 24/7 to piss off The Chief Thief.

                              Comment


                              • Originally posted by abcd567 View Post
                                CONGRTULATIOS for making a very successful and very simple antenna.

                                1)What is the spacing of 3 range rings on your VRS plot?
                                2) what are the dimensions of super-j's upper limb & phasing coil?

                                The black rings are 100 nm....

                                The top is 1/2 wave (134mm) the phasing stub is the same 134mm..
                                To make it .. measure up from the bottom of the J to the top of the first element (I don't have my numbers in front of me but I think it was 188 mm) make a 90 degree turn.. measure another 134 mm and make another 90.. find the center of the middle section and bend it back on itself so that the top element is back on top of the bottom element (straight up and down antenna with a 1/2 stub sticking out the middle... that is it.. you can coil the center stub to make if look like the one in the picture and it will fit inside of a PVC tube.

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