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  • Originally posted by HermanZA View Post
    Looking forward to your results! Might be making myself another CoCo this weekend, and can just maybe benefit from your tests.
    It will take a bit longer, I'm trying each model over a long time period (a whole week, 168 hours test run) to avoid inconvenient situations: low density traffic, poor propagation, etc.
    Northwest Spain: F-LECO1, F-LEST1

    Comment


    • Originally posted by Breitling View Post
      I'm conducting the comparative test that abcd456 proposed some time ago. Different Coco tip terminations, all of them made with the same cable type, same location, same receiver, etc. I'll prepare a specific webpage to show them all with gathered data.

      Just an image to make audience

      [ATTACH=CONFIG]4393[/ATTACH]
      Originally posted by Breitling View Post
      It will take a bit longer, I'm trying each model over a long time period (a whole week, 168 hours test run) to avoid inconvenient situations: low density traffic, poor propagation, etc.
      Thanks for your efforts which will benefit all of us. You are thorough & dilligent. Waiting for your results.

      Comment


      • It just occurred to me that coaxial collinear antenna made of coaxial cable is a compromise.

        For any element of the coco, the central conductor is used for phasing & should be 1/2 wavelength.
        As the phasing function is carried out by inner space of the coaxial where the electromagnetic field is totally confined in the dielectric between core & shield, the required length is 1/2 wavelength in air (138 mm) x Velocity factor of the dielectric. If VF is 0.85, the length should be 117mm

        The outer surface of the shield of that very element is used for receiving the incoming electromagnetic field. Its length should also be 1/2 wavelength. Since the incoming field is totally in the space between antenna & aircraft, and is in air, Velocity factor is 1. Hence the length should be 1/2 wavelength in air = 138mm.

        We are making CoCos with element length using Velocity factor of Coaxial Cable. This makes the phasing element (inner space) accurately dimensioned (117mm), but makes the receiving element (outer surface of shield) shorter than optimum (117mm instead of required 138mm).

        The CoCo will be precise & optimum only if inside dielectric is air.
        If the elements are made of hollow metallic tube with central conductor supported by few rings/washers of plastic or rubber, this can be achieved.

        Air Insulated CoCo.png

        .

        Comment


        • ABCD, you got me totally confused now. (admitting, you have done so on a few occasions in the past as well! )

          So you say that the VF we used was based on the cable specs, and not the fact that the majority of the EM signal is travelling through open space (with a VF of 1.0), so we are using elements that are shorter than what it should be. On the Antenna itself.
          Based on that, should we then not consider that the signal received by the antenna, travels through a cable to the receiver, and the VF factor rule comes into play, cause we are now constraining it in a cable? Me thinks: optimal reception on the antenna, then we 'throttle' it through whatver cable, messing the perfect signal up.

          So you are proposing we should look at new antenna specs, with 138mm element lenghts, built of say an aluminium tube (of what diameter?) with rubber (non conductive) spacers to hold a centre element (copper perhaps?) in place. Based on this, what number of elements, and also a 5 1/2 element design?

          Comment


          • Originally posted by HermanZA View Post
            ABCD, you got me totally confused now. (admitting, you have done so on a few occasions in the past as well! )

            So you say that the VF we used was based on the cable specs, and not the fact that the majority of the EM signal is travelling through open space (with a VF of 1.0), so we are using elements that are shorter than what it should be. On the Antenna itself.
            Based on that, should we then not consider that the signal received by the antenna, travels through a cable to the receiver, and the VF factor rule comes into play, cause we are now constraining it in a cable? Me thinks: optimal reception on the antenna, then we 'throttle' it through whatver cable, messing the perfect signal up.

            So you are proposing we should look at new antenna specs, with 138mm element lenghts, built of say an aluminium tube (of what diameter?) with rubber (non conductive) spacers to hold a centre element (copper perhaps?) in place. Based on this, what number of elements, and also a 5 1/2 element design?

            With Dielectric Insulated elements, there is a conflict in element length due to difference in inner & outer mediums (138mmxVF for dielectric inside & 138mm for air outside).

            With air as dielectric both inside & outside the element, both lengths become same (138mm) & this conflict will resolve.
            Please see attached sketch below.

            The design will remain same, number of elements according to your choice. Only the material used for making the elements is copper/aluminum/brass tube with inner conductor also of copper/aluminum/brass, held in place by insulating spacers. The length of elements will be 138 mm.

            As far as feed cable is concerned, it does not perform receiving & phasing functions & hence there is no conflict.

            Air Insulated CoCo-2.png

            Later addition:
            The electromagnetic field INSIDE the cable is produced by the current flowing in the central conductor. This field is totally confined within the cable in the space between central conductor & shield.

            The electromagnetic field OUTSIDE the cable is produced by the aircraft antenna, and is totally in air outside the cable. It does not penetrate into the space inside the shield. The outer surface of the shield is the actual receiving antenna
            Last edited by abcd567; 2014-07-21, 16:50.

            Comment


            • Hello, someone can tell me what amplifier serves to 1090mhz?
              Thank you

              Comment


              • That would be an Satellite dish LNB amplifier like this one http://www.ebay.co.uk/itm/350657754545

                A satellite receiver passes 13v - 19v up the wire to the LNB (Low Noise Block) mounted on the dish. 13v says please receive vertically polarised signals, 19v horizontal signals. In addition the receiver will put a 22Khz audio signal up the wire to tell the LNB to switch to hi-band. Now these amplifiers are designed to work in that environment - so we need to put 15v-18v up the wire to run the amplifier, and the amplifier will pass that voltage on to run the LNB. We can't just connect the supply to the coax since it will also pass the power back down to the dongle and it won't like it. We might also have to protect the antenna from the voltage that would go to the LNB.

                So,

                we need a line power inserter to add power to the coax http://www.ebay.co.uk/itm/161044085914 - but not to pass it to the dongle ... and a 15v-18v power supply http://www.ebay.co.uk/itm/120976304351 (may need work to make the plugs fit????)

                we may need a DC voltage blocker http://www.ebay.co.uk/itm/171258939281 if our antenna presents a resistance to a DC test.
                Last edited by peterhr; 2014-07-21, 18:35.

                Comment


                • Towards the end of last year, I got an Antenna Manufacturer to build me a 1090 mHz antenna. Paid a small fortune for the darn thing, but was promised at least 9dB gain with it. Had it up and down a few times, never could quite get proper reception with it, so summised it might got damaged in transit, maybe just a bad connection or something, as the N connector at the bottom did not feel proper.
                  Today I took it down, opened the top end and tested for continuity.

                  From N-connector at the base: From centre to top centre element - No continuity.
                  From N-connector at the base: From outer to top centre element - Continuity. This did not seem right, as I expected centre to top to give a result.

                  So I took the thing apart. Using destructive means, as I could not undo it any other way.
                  Eureka! This aint a colinnear antenna... its a J-pole. Another moment!

                  Read up on J-poles tonight... not much the wiser, to be quite honest. Discovered this might be a Super J-pole. Now since I never got any decent reception with this thing (with or without the amplifier), was it a case of maybe a bad antenna, or maybe me not wiring it correctly, or just a flawed design/construction? I cant understand how this works, or why a J-pole would be better than a collinear. I cant see the active part that picks up a signal, as its basically a short, with the inner and outer of the cable connected to the same wire... didn't even bother measuring the lenghts of the elements or the coils.

                  Those of you with more antenna knowledge, please share your ideas and thoughts on this matter.

                  jpole2.jpg
                  Last edited by HermanZA; 2014-07-21, 21:52.

                  Comment


                  • Originally posted by abcd567 View Post
                    It just occurred to me that coaxial collinear antenna made of coaxial cable is a compromise.

                    For any element of the coco, the central conductor is used for phasing & should be 1/2 wavelength.
                    As the phasing function is carried out by inner space of the coaxial where the electromagnetic field is totally confined in the dielectric between core & shield, the required length is 1/2 wavelength in air (138 mm) x Velocity factor of the dielectric. If VF is 0.85, the length should be 117mm

                    The outer surface of the shield of that very element is used for receiving the incoming electromagnetic field. Its length should also be 1/2 wavelength. Since the incoming field is totally in the space between antenna & aircraft, and is in air, Velocity factor is 1. Hence the length should be 1/2 wavelength in air = 138mm.

                    We are making CoCos with element length using Velocity factor of Coaxial Cable. This makes the phasing element (inner space) accurately dimensioned (117mm), but makes the receiving element (outer surface of shield) shorter than optimum (117mm instead of required 138mm).

                    The CoCo will be precise & optimum only if inside dielectric is air.
                    If the elements are made of hollow metallic tube with central conductor supported by few rings/washers of plastic or rubber, this can be achieved.

                    [ATTACH=CONFIG]4420[/ATTACH]

                    .
                    Don't be too despondent F-EGLF1 has been doing practical lab tests on built antennas and has shown that your calculations can't be too far off. The results prove the theory. If theory was the end result - we would had the Higgs-Boson long ago.

                    Comment


                    • Originally posted by HermanZA View Post
                      Read up on J-poles tonight... not much the wiser, to be quite honest. Discovered this might be a Super J-pole. Now since I never got any decent reception with this thing (with or without the amplifier), was it a case of maybe a bad antenna, or maybe me not wiring it correctly, or just a flawed design/construction? I cant understand how this works, or why a J-pole would be better than a collinear. I cant see the active part that picks up a signal, as its basically a short, with the inner and outer of the cable connected to the same wire... didn't even bother measuring the lenghts of the elements or the coils.

                      Those of you with more antenna knowledge, please share your ideas and thoughts on this matter.

                      [ATTACH=CONFIG]4434[/ATTACH]
                      Hi Herman,
                      The first antenna I built was a J pole. Don't ask me how they work though! Yours looks pretty similar to mine but I didn't have the coils at the top of the long part. Can you measure the lengths of the 2 parts and also the distance from the base to where the coax is attached. Also which side the centre core of the coax is attached to (long or short side).

                      Cheers
                      Trig
                      T-EGUB1

                      Comment


                      • Originally posted by peterhr View Post
                        Don't be too despondent F-EGLF1 has been doing practical lab tests on built antennas and has shown that your calculations can't be too far off. The results prove the theory. If theory was the end result - we would had the Higgs-Boson long ago.
                        I have a bitter experience of CoCos. I have noticed that like me, many other amateurs have experienced unsatisfactory performance from their CoCos

                        I have built more than 6 different CoCos. Some were better than others, but all have miserably failed when compared to other antennas I have built (like simplest 1/2 wavelength dipole, 4 element Franklin, sleeved dipole). I fail to understand why my CoCos don't perform as they should. Is it using low cost cable like RG6, or bad workmanship, or wrong design/dimensions? Is it due to combination of many small factors, or is it one major factor?

                        Comment


                        • How about going for a franklin concept whip with a J at the bottom for impedance matching. Should be able to do something that is robust enough to be self supporting or be able to be supported from a fibreglass rod with 100 - 150 mm standoff's crucially placed zero voltage positions.

                          That should eliminate all velocity factors from the calculations.

                          With my antenna I did place the amplifier at the base of the antenna (ratrher than in line) as much as anythinr to reduce impedance mis-match issues. I'm running with RG6 and I'm getting about as much distance as I could hope for with a dongle - 450km in the good directions with no hills.
                          Last edited by peterhr; 2014-07-22, 19:06.

                          Comment


                          • Hello everyone

                            Just curious

                            The small outdoor antenna for DVB-T signal can capture?

                            Type this

                            http://www.microcubo.com/fotos_produ...ster.1.big.jpg

                            http://www.ebay.com/itm/Active-DVB-T...item4ad7ec5f52

                            http://www.tv-alvitecnica.com/WebRoo...geImg.asp.jpeg

                            Or all antennas even those are limited to 860MHz capture 1090mhz?

                            Thanks

                            Comment


                            • Originally posted by peterhr View Post
                              How about going for a franklin concept whip with a J at the bottom for impedance matching. Should be able to do something that is robust enough to be self supporting or be able to be supported from a fibreglass rod with 100 - 150 mm standoff's crucially placed zero voltage positions.......
                              J-Pole is a monopole+matching stub minus ground-plane. Performance of any monopole/whip without ground plane is inferior to a dipole or a monopole+groundplane.
                              Last edited by abcd567; 2014-07-22, 20:08.

                              Comment


                              • Originally posted by ptruicp View Post
                                Hello everyone

                                Just curious

                                The small outdoor antenna for DVB-T signal can capture?

                                Type this

                                http://www.microcubo.com/fotos_produ...ster.1.big.jpg

                                http://www.ebay.com/itm/Active-DVB-T...item4ad7ec5f52

                                http://www.tv-alvitecnica.com/WebRoo...geImg.asp.jpeg

                                Or all antennas even those are limited to 860MHz capture 1090mhz?

                                Thanks
                                They probably wouldn't perform anything like as well as a tuned antenna at the right frequency

                                Originally posted by abcd567 View Post
                                J-Pole is a monopole+matching stub minus ground-plane. Performance of any monopole/whip without ground plane is inferior to a dipole or monopole+groundplane.
                                OK, add a [psudo] groundplane - I was just thinking of something that is essentially supported from the bottom (ie on a stick)

                                Comment

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