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  • Originally posted by abcd567 View Post
    .
    DEVELOPMENT OF THE COCO

    Please see sketch below:

    [ATTACH=CONFIG]3924[/ATTACH]

    .
    Now i understood how COCO works really big thanks
    RTL SDR : T-VEVZ1

    Comment


    • I've made two collinear aerials now and they always look horrible on the analyser they work, but not as well as the first one i posted (post #782). I'm trying to work out what i'm doing wrong be it cable or method.

      Going to try a franklin then dipole it if you know what i mean and see what happens.
      T-EGLF8

      Comment


      • Originally posted by SpaxmoidJAm View Post
        I've made two collinear aerials now and they always look horrible on the analyser they work, but not as well as the first one i posted (post #782). I'm trying to work out what i'm doing wrong be it cable or method.

        Going to try a franklin then dipole it if you know what i mean and see what happens.
        My first attempts at CoCos were not very efficient. Since then, I always check each segment I attach with a meter to make sure I get continuity where appropriate and no shorts. It is very easy to get a whisp of screen at the joints. I then check the whole antenna once I've wrapped the joints with tape.

        I've built a couple (or three) Franklins and found their performance to be superior to everything else I've built.

        Are you Farnborough, Hants? I used to live in Cove.

        Welcome to the "wire benders" club.
        Dave
        T-EGUB1

        Comment


        • Originally posted by trigger View Post
          My first attempts at CoCos were not very efficient. Since then, I always check each segment I attach with a meter to make sure I get continuity where appropriate and no shorts. It is very easy to get a whisp of screen at the joints. I then check the whole antenna once I've wrapped the joints with tape.

          I've built a couple (or three) Franklins and found their performance to be superior to everything else I've built.

          Are you Farnborough, Hants? I used to live in Cove.

          Welcome to the "wire benders" club.
          Dave
          I am as good as yes. I live only a few miles away.



          I'm sure there are no shorts but the continuity is probably an issue when moving them around to test. I think if i made them with a mind to being more permanent they would fair better.

          I'm quite keen to try and make one without coax apart from being bigger because of the VF being essentially 1. You should be able to make one from 15mm pipe and some solid copper wire. Just want to see if it works as i have enough off cuts of pipe that its worth a go.
          Last edited by SpaxmoidJAm; 2014-04-21, 08:42. Reason: spelling
          T-EGLF8

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          • just been thinking, i've been using RG59 because i had some lying around, it doesn't have a foil rapping around it under the braid. I wander how much of an effect that has?
            T-EGLF8

            Comment


            • Originally posted by SpaxmoidJAm View Post


              I'm sure there are no shorts but the continuity is probably an issue when moving them around to test.
              On one of the CoCos I subsequently dismantled I found that the core had snapped on a couple of joints. The coax I'm using has quite a brittle core and I guess I knicked it when cutting the insulation.

              Let me know how you get on with the copper pipe idea. I've wondered about it too. I guess you could use some dowel run up through the pipe to support it?
              T-EGUB1

              Comment


              • supporting it would be a issue, i was think where the section meet using a small piece of something as an isolator it might then self support,

                just found this website quite a good read some of it has sunk in.

                http://www.radio-electronics.com/info/antennas/
                T-EGLF8

                Comment


                • having read this a j-pole can be made very easily

                  http://www.radio-electronics.com/inf...le_antenna.php

                  the j part does not need to be shorted.

                  WP_20140421_002.jpg

                  it instantly got me the same number of planes took 10 mins to make just need to see what range it gets. I'll repeat the build at work and stick it on the analyser.

                  I'm ignoring the impedance matching aspect because i am using a 5cm patch cable to the dongle.

                  The aerial although initially looked good does not have the range. so i have taken it down with the amount of aircraft up at the minute i was hoping for better than 50nm with it.
                  Last edited by SpaxmoidJAm; 2014-04-21, 12:45. Reason: it didnt work that well
                  T-EGLF8

                  Comment


                  • @abcd567
                    on page 20 of this document it has a slightly different arrangement could you simulate it and see if it wrong or right.
                    http://www.146970.com/PDFs/Antenna%2...na%20Ideas.pdf
                    T-EGLF8

                    Comment


                    • Originally posted by SpaxmoidJAm View Post
                      ...........but the continuity is probably an issue when moving them around to test. .........
                      After assembly, I taped my CoCos to a either a thin wooden stick (one used to support a creeper plant) or to a wooden board.
                      This kept it straight & prevented its parts from dislodging or breaking. I have applied tape to each individual piece to prevent motion.

                      Comment


                      • Originally posted by SpaxmoidJAm View Post
                        @abcd567
                        on page 20 of this document it has a slightly different arrangement could you simulate it and see if it wrong or right.
                        http://www.146970.com/PDFs/Antenna%2...na%20Ideas.pdf
                        @SpaxmoidJAm
                        The design suggests a 1/2 wavelength shorted stub for Impedance matching.
                        Never came across 1/2 wavelength matching stub.
                        The 1/4 wavelength matching stub is almost universal.
                        Anyway, will soon simulate the Franklin with 1/2 wavelength impedance matching stub to see how it performs.
                        Maybe it proves better than 1/4 wave matching stub.
                        Last edited by abcd567; 2014-04-21, 12:53.

                        Comment


                        • Originally posted by SpaxmoidJAm View Post
                          having read this a j-pole can be made very easily

                          http://www.radio-electronics.com/inf...le_antenna.php

                          the j part does not need to be shorted.

                          [ATTACH=CONFIG]3928[/ATTACH]

                          it instantly got me the same number of planes took 10 mins to make just need to see what range it gets. I'll repeat the build at work and stick it on the analyser.

                          I'm ignoring the impedance matching aspect because i am using a 5cm patch cable to the dongle.
                          Without impedance matching there will be reduced flow of signal to low load impedance of the Dongle (75 ohms). Impedance matching is not only antenna to cable. It is matching between antenna & receiver (dongle) as well.

                          Comment


                          • i'll agree with you it doesn't really seem to have much in the way of range 50NM which i have tripled with another aerial is not so good. That being said it was as good as a incredibly easy one to make.
                            T-EGLF8

                            Comment


                            • Originally posted by abcd567 View Post
                              ANOTHER EXPERIMENTAL DESIGN - 6 ELEMENT COILED DIPOLE.
                              FITS INSIDE 25mm PVC PIPE


                              NOT BUILT & TESTED YET

                              Gain = 8.5 dB in horizontal direction, SWR = 1.65

                              SEE BELOW SCREENSHOTS OF COMPUTER SIMULATION USING 4NEC2 SOFTWARE
                              (available free of cost at http://www.qsl.net/4nec2/)
                              :


                              SIMULATION OUTPUT: ANTENNA LAYOUT, SWR, GAIN, & PATTERN
                              [ATTACH=CONFIG]3760[/ATTACH]

                              INPUT: DIMENSIONAL DATA OF ANTENNA, FREQUENCY, CABLE IMPEDANCE, CABLE CONNECTION POINT
                              [ATTACH=CONFIG]3761[/ATTACH]

                              .
                              this aerial here, i have just made i am assuming that one is connected to the shield of the coax? To get any real analyser results it will have to wait until Friday, cant get this one on me bicycle
                              T-EGLF8

                              Comment


                              • Finished my testing with the 3 element CoCos to try to work out the Velocity Factor of the coax I have. I've settled on an element length of 94mm which gives a velocity factor of 68%.

                                I've just, very carefully, made an 8 element CoCo with open top and put it on test. The first 20 minutes suggest it is as good as the Franklin I am using as my "one to beat" Will post graphs later after the thunderstorm moves through!

                                I have the graphing function of adsbScope running as a quick check to see if the frames per minute goes up or down as I swap antennas. There are 2 lines on the plot. One Blue (fpm) and the other Green (fpma). What is fpma? Is it Frames Per Minute Average? All the CoCos I've been testing have had the green line above the blue line. With the 8 element CoCo I've just built, the blue line is way above the green one now.
                                Cheers
                                Dave
                                T-EGUB1

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