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  • Originally posted by F-EGLF1 View Post
    Just for comparison this is what I am getting with the official FR24 kit, taken over about 2 hours. (I cannot plot for longer as ADSBscope bombs every few minutes, I think the framerate is too high, it reaches 145,000 or more and I have to disconnect and re-connect the raw data feed)
    [ATTACH=CONFIG]3944[/ATTACH]

    (If anyone knows how to get ADSBscope running for longer I would love to know)
    My framerate runs about 10 - 15,000 fpm with about 80 - 110 aircraft during the day. I have no idea why your adsbScope bombs but you may be right about the high framerate.

    You appear to be getting perfect coverage which I suppose is to be expected with proper kit. Do you have a good view of the horizon in all directions?
    Last edited by trigger; 2014-04-23, 07:33.
    T-EGUB1

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    • Originally posted by trigger View Post
      My framerate runs about 10 - 15,000 fpm with about 80 - 110 aircraft during the day. I have no idea why your adsbScope bombs but you may be right about the high framerate.

      You appear to be getting perfect coverage which I suppose is to be expected with proper kit. Do you have a good view of the horizon in all directions?
      I see 200-250+ aircraft at any one time during the day (both Heathrow and Gatwick are close to me).
      I am lucky in that I am on high ground with a virtually unrestricted view (a small hill to the S/W only), I would love to be able to do a full 24-hour plot to see my full range, but I am not dissatisfied with my coverage.
      Ben.
      FR24 F-EGLF1, Blitzortung station 878, OGN Aldersht2, PilotAware PWAldersht, PlanePlotter M7.

      Comment


      • @lutorm:
        @Birdie
        I have not yet completed my studies on Reflection Phenomenon. My initial study's results are below (This opinion may change on further studies):

        Propagation of RF Energy in a dielectric medium (such as air & vacuum) takes place by changing Electric & Magnetic Fields, called electromagnetic waves. No motion of electrical charge is involved. When these electromagnetic waves reach a boundary of the medium with another medium (dielectric or conducting) reflection takes place, and standing waves are produced. This is a physical phenomenon. An everyday example is reflection of light (also an electromagnetic wave) by a mirror or a reflective surface.

        Propagation of RF Energy in metals (wires) takes place by moving electric charge (i.e electrons). These electron do not get reflected at the boundary of two metals such as transmission line & antenna.

        The origins of Reflected & Standing waves are from propagation of RF in DIELECTRIC, where this is a PHYSICAL phenomenon. The calculation techniques developed using this phenomenon were so powerful & successful, that these were successfully applied by ANALOGY to propagation of RF Energy on wires also, although it does not physically occur there.

        As regard impedance matching & power flow in metal (wires) circuits, it is a very fundamental law covering from frequency = 0 (DC) to microwave+ that "maximum power flows when load & source impedance are equal". This was established much before the discovery of Radio Waves.

        Quote:
        "In electrical engineering, the maximum power transfer theorem states that, to obtain maximum external power from a source with a finite internal resistance, the resistance of the load must equal the resistance of the source as viewed from its output terminals. Moritz von Jacobi published the maximum power (transfer) theorem around 1840; it is also referred to as "Jacobi's law""

        For details, please see http://en.wikipedia.org/wiki/Maximum...ansfer_theorem

        Please note that DC is NOT Electrostatic (electrostatic=no motion of electric charge, like a charged open-circuited capacitor). It is Electrodynamic as it involves motion of charge (electrons) in a wire, like RF on wire involves motion of charge (electrons).
        Last edited by abcd567; 2014-04-23, 17:59.

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        • j-pole results are in.

          not to bad for two strait pieces of wire.
          j_pole.jpg
          T-EGLF8

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          • Originally posted by SpaxmoidJAm View Post
            j-pole results are in.

            not to bad for two strait pieces of wire.
            [ATTACH=CONFIG]3948[/ATTACH]
            Excellent! Can you please post photos & dimensions of wires (lengths, dia, spacing etc)? I want to make one & give it a try.

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            • It's true that electrons don't get reflected. But they also move very slowly. There is no contradiction between a wave reflecting and its carriers not. Sound waves reflect off surfaces, but the motion of the air molecules associated with the wave is microscopic.

              The best experiment I know that demonstrates wave mechanics, including impedance mismatching, is the "slinky spring" (if you remember). Like this one: http://exs.exploratorium.edu/exhibits/giant-slinky/. If you join two such springs of different diameter and put a wave into it, you can see the wave partially reflecting at the mismatch point. You might think this isn't a valid analogy, but the cool thing about wave mechanics is that the underlying mathematics are the same for all wave motions, so the same phenomena appear. Why does light partially reflect at a glass surface? Because the glass presents a different "impedance" to the EM wave than air does.

              But you are wrong about electrostatics. From wikipedia:
              Electrostatics is a branch of physics that deals with the phenomena and properties of stationary or slow-moving electric charges with no acceleration.
              The no acceleration is the key. It's perfectly fine to have currents in an electrostatic situation, as long as the current doesn't vary in time.
              Patrik J. / KB1VGP / FR24 T-PHTO1

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              • yep here ya go.
                WP_20140423_004a.jpg
                the lengths are from where the dielectric clears the bnc connector (I've written 136 on the drawing should 138 finger trouble). i imagine the gap between the wire might matter but considering how simple it is.

                also i have finally made a decent collinear, rather than pushing the two coax together i have soldered them like below and it instantly far more stable. So for me it was definitely a continuity issue.
                WP_20140423_002a.jpg

                and showing rather good results its a three element with a short on the 1/4 at the end.
                Last edited by SpaxmoidJAm; 2014-04-23, 19:12.
                T-EGLF8

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                • ...
                  by not inserting the two parts fully, you are lengthening the elements.. so won't be resonant :-(

                  Sent using Tapatalk from my ZX81

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                  • Originally posted by SpaxmoidJAm View Post
                    yep here ya go.

                    the lengths are from where the dielectric clears the bnc connector....... also i have finally made a decent collinear..........and showing rather good results its a three element with a short on the 1/4 at the end.
                    Congratulations for making a good CoCo. Thanks for posting dimensions/photo of J-Pole.

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                    • Is anyone here know how to build a simple airband antenna?
                      118-136mhz...

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                      • Originally posted by Rooster View Post
                        ...
                        by not inserting the two parts fully, you are lengthening the elements.. so won't be resonant :-(

                        Sent using Tapatalk from my ZX81
                        The length of the section doesn't change.

                        see this image. might clear thing up.

                        solder_element_diagram.jpg
                        i got that image from here so credit to them, i just wasn't using the brass sleeving same principle.
                        http://www.nodomainname.co.uk/Omnico...4collinear.htm

                        OK so my unshielded gaps are a little bigger but its doing well, easily the best aerial I've made so far. Come Friday I'll get it on the analyser and so how far off it is.
                        Last edited by SpaxmoidJAm; 2014-04-23, 20:58. Reason: Corrected my self
                        T-EGLF8

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                        • >the length of the section...

                          of course it does, the Join is calculated to be near zero, so by making the gap bigger, the elements are longer!

                          Sent using Tapatalk from my ZX81

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                          • Originally posted by Rooster View Post
                            >the length of the section...

                            of course it does, the Join is calculated to be near zero, so by making the gap bigger, the elements are longer!

                            Sent using Tapatalk from my ZX81
                            Well, because both wires are exposed, it should work like a short piece of transmission line between the elements. However, it will be mismatched to the coax sections, which is bad.
                            Patrik J. / KB1VGP / FR24 T-PHTO1

                            Comment


                            • Originally posted by lutorm View Post
                              .........But you are wrong about electrostatics. From wikipedia:

                              The no acceleration is the key. It's perfectly fine to have currents in an electrostatic situation, as long as the current doesn't vary in time.
                              Yes, according to Wikipedia defination, DC falls under defination of Electrostatics. But how authentic and accurate is this defination? I have my doubts about it's authentecity and accuracy for following reasons:

                              (1) The very name "Electro-static" implies static electricity or no motion of electrical charge.
                              (2) Traditionally DC was never classified under it.
                              (3) The term "very slow" has been used by wikipedia without quantifying. How slow (in meters per seconds) is very slow?
                              (4) I have made a quick check of meaning of "Electrostatic" in Mariam-Webster & Oxford Dictionaries, both catogarily exclude any motion of charge, ( which in turn excludes both DC & AC from category of Electrostatic).

                              Mariam-Webster Dictionary:
                              physics that deals with phenomena due to attractions or repulsions of electric charges but not dependent upon their motion.

                              Oxford Dictionary:
                              The study of stationary electric charges or fields as opposed to electric currents.
                              Last edited by abcd567; 2014-04-23, 23:17.

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                              • Heh, I just pulled out my copy of Jackson's "Classical Electrodynamics" to see what he says, and he seems to split things up into "electrostatics" which is what you are describing (stationary charges), "magnetostatics", which is what I'm thinking of (stationary currents and fields), and finally "electrodynamics", which is the treatment of time-dependent fields and the link between the electric and magnetic fields. So you're right, it seems there's no clear definition.

                                The key change in behavior happens when the wavelength (ie speed of light / frequency) becomes small compared to the size of the system. For these purposes, 60Hz AC is like DC, because the wavelength is 5 million km. That's what makes it possible to use Kirchoff's law's, for example to assume that the current along a conductor has the same value everywhere. Once the wavelength becomes comparable to the size of the system that is no longer true, because now things change on the same time scale it takes the current or voltage to propagate from one place to another.
                                Patrik J. / KB1VGP / FR24 T-PHTO1

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