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  • Originally posted by charan View Post
    Today i made a discovery of my coax ! while i removed 1 element in 8.5 coax and i kept it on my table.. today i kept my mobile over it and when i took mobile the element came with the mobile (attached to speaker).. is this common or i have a cheap coax? will this have any effect on range of my antenna?
    i ordered RG402 yesterday.! [ATTACH=CONFIG]4030[/ATTACH]
    This is common with cheaper coax, the better ones are pure copper, the cheaper ones are copper plated steel, provided the screening is good then it should not have much impact on your range.
    Ben.
    FR24 F-EGLF1, Blitzortung station 878, OGN Aldersht2, PilotAware PWAldersht, PlanePlotter M7.

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    • Originally posted by F-EGLF1 View Post
      This is common with cheaper coax, the better ones are pure copper, the cheaper ones are copper plated steel, provided the screening is good then it should not have much impact on your range.
      Ben.
      Ohh thanks
      RTL SDR : T-VEVZ1

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      • Amazed with the knoweldge in this forum, I follow you all with interest. I'm just another amateur with some aviation relations, trying to catch up everything around me in the air. I have a self made coco antenna and I'd like to know how it performs compared with other designs already showed here. My coco is made with 75ohm coax, half wave elements, 8 in total. At first I left the tip open, but performance was very poor. Now it is shorted with a 75ohm resistor, getting about 150 nm range. What do you think about shorting the tip with a resistor?
        Northwest Spain: F-LECO1, F-LEST1

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        • Originally posted by Breitling View Post
          Amazed with the knoweldge in this forum, I follow you all with interest. I'm just another amateur with some aviation relations, trying to catch up everything around me in the air. I have a self made coco antenna and I'd like to know how it performs compared with other designs already showed here. My coco is made with 75ohm coax, half wave elements, 8 in total. At first I left the tip open, but performance was very poor. Now it is shorted with a 75ohm resistor, getting about 150 nm range. What do you think about shorting the tip with a resistor?
          We discussed this a few pages back - the calculations showed 7.5 elements with a shorted top may be better.

          The trick with experimental coco's is not to seal them into a tube until the design is fully tweaked - that way you can access then to adjust them.

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          • Originally posted by Breitling View Post
            Amazed with the knoweldge in this forum, I follow you all with interest. I'm just another amateur with some aviation relations, trying to catch up everything around me in the air. I have a self made coco antenna and I'd like to know how it performs compared with other designs already showed here. My coco is made with 75ohm coax, half wave elements, 8 in total. At first I left the tip open, but performance was very poor. Now it is shorted with a 75ohm resistor, getting about 150 nm range. What do you think about shorting the tip with a resistor?
            Please click here to see post #843

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            • Thank you very much abcd567, I asked because none of them are like mine one. Mine is 8 element shorted top, and as a complete ignorant in this theme I don't know if there is any difference between simply shorting braid and core or doing it with a resistor. Built exactly as shown here: http://www.balarad.net/
              Northwest Spain: F-LECO1, F-LEST1

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              • just to show how much height and obstacles make with regard to aerial placement.

                This is the 3.5 shorted copy aerial (F-EGLF1's) in my loft space, on 1meter of coax strait into TV dongle. Not as good as hoped.
                3.5copy.jpg
                This is the same aerial on my roof with 10meters of h155 coax
                copy3.5_roof.jpg
                It easily added 50NM miles in the couple of hours i had to run the aerial it had to come down because of the work being done. It also was getting dark and i didn't want to be on the scaffold in the dark.

                I could not get the aerial in the best position because of work being done on the roof and where i passed the cable out of a window to the roof the cable simply wasnt long enough, you will have to excuse the TV aerial as it had to be moved out of the way of the scaffolding so that's why its leaning over and the cables are loose.

                The pole is actually a extending handle for window cleaning was all of about 15 euro's and extents to 3.6meters
                P1000638_small.jpg
                here you can see my main aerial and in the background to the right the copy, its doesnt quite clear the roof line to south of me which is why i was surprised to get 50NM in that direction.
                roof_blocked.jpg

                So by adding height and some attenuation (not good) by the extra cable length, the range was extended considerably. This was with a decreasing number of aircraft too. Also the number of planes seen went from a 1/3 of my radar cape to 1/2 a good improvement there too.
                Last edited by SpaxmoidJAm; 2014-05-06, 21:10. Reason: Put the wring picture up.
                T-EGLF8

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                • Originally posted by lutorm View Post
                  Thanks! I'm pretty happy with how it turned out. Not professional by any means though -- strictly amateur!

                  Not sure about the amplifier. It looks pretty well sealed, but in any case it was 6 bucks, including shipping from China, so if it gives up it's not a big deal. Given that I live in one of the rainiest towns in the US, we should find out soon. The picture is from this post, which has some more info. Nothing that people here doesn't already know, though.
                  The DC in coaxial cable gets shorted by matching stub of Franklin, unless a DC isolating arrangement (generally a capacitor) is inserted between amplifier & antenna. In antenna's photo this is not visible. Is the capacitor at the point where coax connects to antenna (also not visible in the photo)?

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                  • Originally posted by abcd567 View Post
                    The DC in coaxial cable gets shorted by matching stub of Franklin, unless a DC isolating arrangement (generally a capacitor) is inserted between amplifier & antenna. In antenna's photo this is not visible. Is the capacitor at the point where coax connects to antenna (also not visible in the photo)?
                    The Franklin is split in the center. I wondered what this would do, but the EZNEC calculation showed a better match to 75ohm than with it shorted (with appropriate feedpoint adjustment), and empirically it certainly did not get any worse with it open than shorted.
                    Patrik J. / KB1VGP / FR24 T-PHTO1

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                    • Originally posted by lutorm View Post
                      The Franklin is split in the center. I wondered what this would do, but the EZNEC calculation showed a better match to 75ohm than with it shorted (with appropriate feedpoint adjustment), and empirically it certainly did not get any worse with it open than shorted.
                      I have done this excersise couple of months ago by trial runs. My results show that a shorted stub is somewhat better than an open stub. Please see my post #615
                      http://forum.flightradar24.com/threa...ll=1#post44013.
                      Last edited by abcd567; 2014-05-07, 08:32.

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                      • Originally posted by abcd567 View Post
                        I have done this excersise couple of months ago by trial runs. My results show that a shorted stub is somewhat better than an open stub. Please see my post #615
                        http://forum.flightradar24.com/showt...?p=44013<br />.
                        Did you adjust the 18mm in that figure? With the EZNEC simulation, I ended up with 10mm spacing between the lines and attaching 6mm in from the end as the best alternative. But this also depends on the diameter of the wire.
                        Patrik J. / KB1VGP / FR24 T-PHTO1

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                        • Originally posted by lutorm View Post
                          Did you adjust the 18mm in that figure? With the EZNEC simulation, I ended up with 10mm spacing between the lines and attaching 6mm in from the end as the best alternative. But this also depends on the diameter of the wire.
                          All tap positions in those trial runs are reached by actually adjusting tap positions between 10 mm and 30 mm in 2mm steps, and selecting the one which gave best results.
                          P.S. dia of wire I used was 1mm (14 AWG), the core of RG6 coax.
                          Last edited by abcd567; 2014-05-07, 02:13.

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                          • Originally posted by abcd567 View Post
                            All tap positions in those trial runs are reached by actually adjusting tap positions between 10 mm and 30 mm in 2mm steps, and selecting the one which gave best results.
                            P.S. dia of wire I used was 1mm (14 AWG), the core of RG6 coax.
                            Wow, that is a large number of trials. It must have taken a long time. How long did you run each test for to make sure you got enough signal?
                            Patrik J. / KB1VGP / FR24 T-PHTO1

                            Comment


                            • Originally posted by lutorm View Post
                              Wow, that is a large number of trials. It must have taken a long time. How long did you run each test for to make sure you got enough signal?
                              Yes, it was painstaking. Each position about 4 hours run. The whole lot took weeks. At that time i did not have the simulaion software (4nec2) and my only option was tweaking by trial runs.

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                              • Originally posted by abcd567 View Post
                                Yes, it was painstaking. Each position about 4 hours run. The whole lot took weeks. At that time i did not have the simulaion software (4nec2) and my only option was tweaking by trial runs.
                                That's dedication! Did you find that the calculated results agreed with the experimental ones?
                                Patrik J. / KB1VGP / FR24 T-PHTO1

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