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  • A recent example of failure of DIY coco by a novice:

    The gentleman found this design, and was very confident & excited about it:

    http://www.arrl.org/files/file/QST/This Month in QST/January 2014/VirtualRadarJan2013QST.pdf

    The instructions clearly mentioned RG6 coax to be used with element length 4.5 inches (114 mm). He did not realize the importance of VF and cable specs. He had a large quantity of RG59, so he built his coco using RG59, but used element length specified in the instructions, which was for RG6. He ended up in a poor coco.

    RG59 is manufactured both with PloyEthylene & FoamedPolyEthylene. I gave hime photos of both versions & explained the difference between the two. He confirmed his RG59 insulation is PolyEthylene. I told him he should then try 91mm element length, as PE has VF=0.66.

    But he was so much discouraged by the 1st coco's failure, he did not bother to built another coco with different element length. Instead he straight away made a Cantenna, enclosed it inside an empty 100 DVD case, put it up, and is very happy with it. He has now ordered an amplifier also!
    Last edited by abcd567; 2014-12-02, 19:07.

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    • Update:

      I've gradually shortened the element length of a 114mm CoCo made from Sat 100 by chopping ~5mm off at a time and putting on trial monitoring the frame rate and distance over about an hour. The frame rate and distance gradually got better as I chopped more off. The second one has now ended up at 91mm (the same as my best CoCo). I'll now put the 2 CoCos on a 24 hour distance trial to see how repeatable the CoCo build is.
      T-EGUB1

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      • Originally posted by trigger View Post
        Update:

        I've gradually shortened the element length of a 114mm CoCo made from Sat 100 by chopping ~5mm off at a time and putting on trial monitoring the frame rate and distance over about an hour. The frame rate and distance gradually got better as I chopped more off. The second one has now ended up at 91mm (the same as my best CoCo). I'll now put the 2 CoCos on a 24 hour distance trial to see how repeatable the CoCo build is.
        Thanks Dave. I appreciate your hard work and sharing your results. This will benefit all members of the forum. Thanks once again.

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        • I came on the air today and am anxiously awaiting my login credentials so I can see my stats. How long should that take?
          I am an antenna builder par excellence thanks to my AIM UHF analyzer. It takes the guesswork out.
          I looked at the characteristics of the antenna supplied to me and it just doesn't thrill me. Comparison of tracked flights should tell the tale.
          Last edited by K5LEH; 2014-12-03, 00:46. Reason: spelling

          Comment


          • Originally posted by K5LEH View Post
            I came on the air today and am anxiously awaiting my login credentials so I can see my stats. How long should that take?
            I am an antenna builder par excellence thanks to my AIM UHF analyzer. It takes the guesswork out.
            I looked at the characteristics of the antenna supplied to me and it just doesn't thrill me. Comparison of tracked flights should tell the tale.
            WELCOME to the "Best Antenna" forum. Hope your skills to build antennas par excellence, as well as skills to use analyzer, will help other members who are not so skilled, neither have test equipment.

            By the way, your user name resembles call sign of amatuer radio operators. Are you an amature radio operator?
            73 DE abcd
            Last edited by abcd567; 2014-12-03, 05:10.

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            • Originally posted by abcd567 View Post
              By the way, your user name resembles call sign of amatuer radio operators. Are you an amature radio operator?
              73 DE abcd
              Yes I am http://www.qrz.com/db/k5leh

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              • Originally posted by K5LEH View Post
                Wow! Great! Nice to have you in this forum.

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                • Originally posted by K5LEH View Post
                  Alway nice to see another "Hammer Chewer" !!!
                  Welcome aboard.

                  Comment


                  • WORLD's FIRST RADIO TRANSMITTER, FIRST RADIO RECEIVER & FIRST DIPOLE ANTENNA - 1886


                    Photo: Karlsruhe Institute of Technology Archives
                    Radio Magic: Heinrich Hertz used the coil [left] and the antennas [right] to produce and detect electromagnetic radiation outside the visible range.

                    Hertz’s experimental work on the subject began at the Technische Hochschule (now the Karlsruhe Institute of Technology) in Karlsruhe, Germany, in 1886, and proved that electromagnetic waves, which were earlier predicted mathematically by James Clark Maxwell, physically exist.

                    To honour his accomplishment, the unit of frequency is named after him: Hertz, Kilo-Hertz, Mega-Hertz, Gega-Hertz
                    Last edited by abcd567; 2014-12-05, 23:59.

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                    • Hi Guys,

                      I need your help mates I'm feeding with a DVB-Stick (http://www.amazon.de/gp/product/B00F...ilpage_o04_s00) with the delivered antenna. I get some good results (see Attachment). I recently bought a new Antenna (http://www.amazon.de/gp/product/B000...ilpage_o02_s00) . I connected it with a BNC - MCX Adapter and it works good, but not as good as I expected. So I bought an Amp (http://www.amazon.de/gp/product/B001...ilpage_o06_s00), but it seems that this is broken.
                      However, what did I wrong ? I am not an expert in Antennas, so please keep it simple for me*lol*dump_antenna1.jpg
                      Regards,
                      T-EDDE7

                      Debian 8 Server | jetvision ADS-B USB Dongle | ADS-B Collinear Antenna
                      Banana Pi | Mystique SDR R820T2 | stock Antenna

                      Comment


                      • Are you supplying power to the amplifier? Caution that you don't fry the front end of your receiver. It needs to be feed with a blocking power insertion.
                        If you ARE powering the amplifier, be aware this amplifier is intended for satellites which typicaly have a 70 ohm impedance. Your radio is probably 50 ohm. This mismatch will slightly degrade the expected performance but not that much.

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                        • Also it appears your antenna is intended for 2 meters. You need an antenna for 1090Mhz.

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                          • Hi,

                            no - i didn't powered the Amp Hm ok, a 2 meters antenna is maybe better for ATC coms... Thanks K5LEH, will look for an 1090mhz Antenna soon. I found one, but the description is in German: http://www.ebay.de/itm/Scannerantenn...item259abe69a9 (the impedance is 50ohm, freq. is between 25 – 2000 MHz)
                            Last edited by equi; 2014-12-05, 19:41.
                            Regards,
                            T-EDDE7

                            Debian 8 Server | jetvision ADS-B USB Dongle | ADS-B Collinear Antenna
                            Banana Pi | Mystique SDR R820T2 | stock Antenna

                            Comment


                            • Good afternoon everyone.

                              I am new to the forum, and new to ADS-B antenna's, but I am an Extra class ham, with plenty of junk laying around.

                              I am in the final stages of constructing an 8 element Co-Co out of LMR-400 50ohm solid center conductor coax. I have seen many different designs posted, so I wanted to see if I can get some consensus on what you guys have found as best practices.

                              At the moment, it is constructed with 8 elements, cut to 1/2 elec WL. I have a 1/4WL stub attached to the top, and the bottom element is directly connected to more LMR-400 for the feedline.

                              Would it be best to add another 1/4 elec WL stub of coax between the "top" element and the 1/4WL stub?

                              What seems to be the best method for adding a sleeve balun, if one is truly needed?

                              Also, if anyone is interested, I might be able to do some "legit" quantitave testing on a few different design concepts at work, in here:
                              https://lh3.googleusercontent.com/-a...929_123848.jpg
                              with this equipment:
                              https://lh4.googleusercontent.com/-8...204_153715.jpg

                              This chamber is used to do 3D field strength modeling of devices and antennas from 400mhz to 6ghz. for ADS-B uses, we would inject a signal into the antenna across a bandwidth around 1090Mhz, and test the radiation pattern being emitted from the antenna. This would give us antenna gain and radiation patterns to compare multiple design styles against each other.

                              Let me know if you guys want to work something out, I would love to help out however I can.

                              Comment


                              • @zryder94:
                                Welcome aboard!
                                Wow! You got such a professional test equipment, and anechoic antenna test chamber. Lucky fellow!

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