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  • Originally posted by SpaxmoidJAm View Post
    well i fainally got around to testing the one i built of this (short story i forgot to order connectors also forgetting i built it)

    the location i tested isnt the best suited nor was the coax i was using quite long enough but these things only make a minor difference to the antenna.
    [ATTACH=CONFIG]6320[/ATTACH]

    by moving me and the aerial i was only able to move things around by best a db and a few MHz.
    Over a period of last one and half years, I have modeled, simulated and optimized many different types of collinears using 4NEC2 & MMANA-GAL softwares. The simulations showed excellent Gain, SWR & Radiation Pattern for all these.

    As and when I modeled any antenna, I also built it and put to trial run. All failed miserably

    Unfortunately I dont have fancy test equipment to test & tweak my antennas. The only test equipment I have is a multimeter which I purchased for $10.

    The latest example of "Excellent Simulation, Hopeless Prototype" is the wire collinear below, which I simulated & built this weekend, and this also failed miserably as usual


    Last edited by abcd567; 2015-08-09, 03:16.

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    • Whip2.JPG

      I have been using this whip antenna for a while, it is a 3 element wire collinier, when covered with heatshrink it was detuned and needed 60mm trimmed from the top. Now it works perfectly. I also made a 9 element in the same way but the detuning from heatshrink was more severe, and there is not enough top element to trim down. I have been using this whip without any insulation material so it is affected by rain which detunes it .

      Whip.jpg

      I have been working on the de-tuning effect and the velocity factor of heatshrink , and have made another antenna, this time I have used a velocity factor of .94
      I re-calculated all the formulas for the elements and the coils at .94 percent and covered it with heatshrink. Testing today and its working good, but I will need to do some trimming to get it A1 . Will report findings
      Mike
      Burnie, Tasmania

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      • IMPROVING PERFORMANCE OF A COCO BY LOWERING IT's SWR/IMPEDANCE
        It is well known that a large number of DIY CoCo makers get frustrating results, and only a relatively small number get satisfactory or good results. Main reason is high impedance & resulting high SWR which causes the antenna to perform poorly even if it has a high Gain.

        I have tried to find a method to ease out the SWR without using test instruments. I tested it and it gave me an improvement of about 25 to 35%., not optimal, but better than nothing.

        Please see sketches below showing an example of impedance matching using this method. It results in using a piece of coax between 0.75 to 0.9 of the length of halfwave elements of CoCo, and a 2.5 pF Capacitor in series. It is applicable to most CoCos without using test equipments. It requires trying four pieces of coax of lengths (0.75 x VF x 138 mm), (0.8 x VF x 138 mm), (0.85 x VF x 138 mm) and (0.9 x VF x 138 mm), and keep the one which give better results than others. The length of coax piece includes length of F-connector also.

        SKETCH 1 of 2 : IMPEDANCE TRANSFORMATION BY A PIECE OF COAX 0 to 1/2 WAVELENGTH LENGTH




        SHETCH 2 of 2: IMPEDANCE MATCHING / SWR IMPROVEMENT METHOD




        This method uses the fact that a piece of transmission line (Coax) transforms the impedance of antenna connected to it. The value of impedance seen at other end of coax depends on length of piece of coax. The impedance transforms in a cyclic manner, returnig back equal to antenna impedance every 1/2 wavelength. At a particular length in between 0 and 1/2 wavelength, the Resistance transforms to exactly the impedance of coax/receiver, and reactive component transforms from capacitive to inductive. At this point if a capacitor of appropriate value is inserted to cancel the inductive component to zero, only resistive component remains which is equal to system impedance, and stays same along remaining entire length of feed coax.

        .
        Last edited by abcd567; 2015-08-10, 09:33.

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        • .
          GRAPHICAL REPRESENTATION - IMPEDANCE TRANSFORMATION ALONG LENGTH OF COAX

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          • Today I made a new 6-element CoCo. I put it to test WITHOUT amplifier and 12ft/ 4m piece of RG6 coax between CoCo and DVB-T USB Dongle + RPi combo. As usual results were poor (see Image 1 of 3).

            I then inserted a capacitor (1.5 pF ) and a piece of coax (length = 0.85 x 1/2 wavelength) between feed cable & CoCo, bringing it's Impedance down, and thereby improving its SWR. The performace increased considerably (see Image 2 of 3).

            I found the length of coax piece & value of capacitor by trial & error, and a few trials only. If I would have tried more lengths & capacitors, I might have got even better results. The rule of thumb I use is that coax piece's optimum length is somewhere between 0.75 to 0.9 of 1/2 wavelength element of CoCo, & the capacitor 's optimum value lies somewhere between 1 pF and 3 pF.

            Please see Image 3 of 3 showing the impedance matching arrangement.

            The two screenshots of dump1090's gmap were taken with a difference of 2 minutes only, the time taken to insert/remove the capacitor.

            IMAGE 1 of 3- dump1090 gmap, NO Impedance Matching, NO Amplifier




            IMAGE 2 of 3 - dump1090 gmap, WITH Impedance Matching, NO Amplifier




            IMAGE 3 of 3 - Impedance Matching Arrangement

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            • Any photo showing the connection for the ceramic capacitor?

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              • u must have a lot of antennas.....a lot.....got enough spare time to do all tests...dok gitu....

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                • Originally posted by kucengemok View Post
                  Any photo showing the connection for the ceramic capacitor?
                  Here is the photo:
                  Ceramic Capacitor in TV Splitter Housing.PNG

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                  • May give that a go! Should be a few dollars for the ceramic capacitor (may have one in some old equipment somewhere) and the two way splitter shouldn't be any more than AU$10. If I can get a 5% improvement, I'd be happy and any more is a bonus.
                    F-YSWG1 and T-YSWG2

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                    • @YSWG: For your information.

                      2-WAY CABLE TV SPLITTER 5-900MH Digital Analogue Satellite Coaxial Out Connector

                      AU $1.49
                      Free postage
                      From Hong Kong





                      150 Pieces 50V 1PF Ceramic Disc Capacitors Replacement Brown

                      AU $4.23
                      Free postage
                      From Hong Kong




                      1000pcs 50 Values 50V Ceramic Capacitor Assorted kit Assortment Set 1pf-100nf

                      AU $6.41
                      Free postage
                      From Hong Kong

                      Comment


                      • Originally posted by YSWG View Post
                        May give that a go! Should be a few dollars for the ceramic capacitor (may have one in some old equipment somewhere) and the two way splitter shouldn't be any more than AU$10. If I can get a 5% improvement, I'd be happy and any more is a bonus.
                        You will need to prepare several pieces of coax 0.75, 0.8, 0.85, & 0.9 times half wavelength (half wavelength = VF of coax X 138 mm).
                        Start trial by mid range values i.e. Coax piece 0.85 x 1/2 wavelength, and capacitor 2 pF. Then try different pieces. Once you find the piece which gives best performance, start trying different values of capacitor like 1 pF, 1.5 pF, 2pF, 2.5pF.

                        Note: Length of coax piece includes length of F-connector.
                        Last edited by abcd567; 2015-08-25, 19:29.

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                        • Picked up [locally] the two way spitter for AU$13 and the ceramic capacitors in a pack of two for 38 cents. Will need to rebuilt an antenna and fix the cable between the dongle ant antenna.
                          F-YSWG1 and T-YSWG2

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                          • Originally posted by YSWG View Post
                            Picked up [locally] the two way spitter for AU$13 and the ceramic capacitors in a pack of two for 38 cents. Will need to rebuilt an antenna and fix the cable between the dongle ant antenna.
                            It seems you purchased a very good quality splitter, that is why you paid almost 9 times the price of a cheap quality one.

                            Since only the housing of splitter will be used, and the internal electronics will be removed and thrown in garbage, there is no use purchasing a very good quality splitter at 9 times the cost of a cheap one.


                            Is this you YSWG?
                            http://forum.planefinder.net/threads...e-11#post-5932

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                            • Hi all,

                              Can you tell me the parts list said in this project? Or any link to describe this more detailed.
                              https://github.com/Reid-n0rc/ADS-B_L...r/Filter%2BLNA
                              IMG_20150729_081738584.jpg

                              Thanks in advance,
                              Zahidul Hasan.

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                              • Been unable to make the antenna but used the current six element CoCo with 1m of coax before the 2.7pF ceramic capacitor. Noticed an increase in messages by 5-7% but decreased by 40% thanks to rainwater getting into the two-way splitter.

                                dump1090-rpi-rate-6h.png
                                The sharp rise at about 16:30 on the 31st was when I added it
                                dump1090-rpi-rate-24h.pngdump1090-rpi-rate-1h.png
                                Today's decrease is noticeable
                                Last edited by YSWG; 2015-09-03, 09:43.
                                F-YSWG1 and T-YSWG2

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