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Thread: best antenna

  1. #1211
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    Quote Originally Posted by abcd567 View Post
    Saw the pictures. Looks great. Waiting for completion & trial run. please post the photos of balun when you add it,
    I am also looking forward to seing this, and hearing how it performs in the real world, I just ran some more tests on the analyser this lunchtime, I think we have sorted out one of the problems we had before, the cable to the analyser was too short and the resonant frequency of the cable was mucking up the results, now with a longer cable (5m) we are seeing a lovely dip of 8-9db with a -3db bandwith of around 40Mhz, however the elements are slightly long so it is resonating at 1040Mhz, I will shorten them tomorrow, but I am aiming for a center frequency of 1080-1085Mhz then matching the impedence with the baluns to give some uptilt to the lobes, looking at the photo of the commercial one it appears as though they are also doing that, however it is not possible to get an exact measurement from the pictures.
    Also my copy of the current ARRL antenna book just arrived from Amazon today, many more headaches to follow as I try to understand the maths !
    Ben.
    FR24 F-EGLF1, Blitzortung station 878, OGN Aldersht2, PilotAware PWAldersht, PlanePlotter M7.

  2. #1212
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    Maybe someone from 'Antennas' would comment on this ... http://forum.flightradar24.com/threa...-to-the-ground

  3. #1213
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    Haven't heard for quiet some time from "Mississauga (Toronto)" & "Farnborough" guys about progress of their ongoing CoCo projects.
    Last edited by abcd567; 2014-06-06 at 22:25.

  4. #1214
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    its on going, were just busy with the actual work weir actually paid to do. It's a pain but it messes with the fun side of stuff.
    T-EGLF8

  5. #1215
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    Quote Originally Posted by SpaxmoidJAm View Post
    its on going, were just busy with the actual work weir actually paid to do. It's a pain but it messes with the fun side of stuff.
    Thanks. Was just curious.

  6. #1216
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    A FAILED EXPERIMENT - ADDING SLEEVE BALUN TO COCO
    I have just now finished 8 hour trial runs of my old CoCo (3.5 element, 11cm element length) with & without Sleeve. The screenshots of VRS are given below. To me it looks that adding sleeve has improved near-range slightly, while removing Sleeve has improved far-range slightly, but the differences are marginal.

    Note: The range rings are 50 kms apart. The outermost blue range ring is 450 kms from receiver.

    Screenshot 1 of 2 : No Sleeve Balun
    coco 11cm 3.5elem NO balun-R.png


    Screenshot 2 of 2 : With Sleeve Balun
    coco 11cm 3.5elem with sleeve balun-R.png
    Last edited by abcd567; 2014-06-15 at 19:20.

  7. #1217
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    Sleeve Balun Costruction Details
    ..... And here are the construction details of the Sleeve....
    The length of Sleeve (i.e. cut length of Pepsi tin) is 6.9 cm (λ/4 in air VF=1)

    picture 1 of 5
    DSC03167.jpg

    picture 2 of 5
    DSC03168.jpg

    picture 3 of 5
    DSC03170.jpg

    picture 4 of 5
    DSC03171.jpg

    picture 5 of 5 - Fully Assembled
    DSC03172.jpg
    Last edited by abcd567; 2014-06-15 at 19:30.

  8. #1218
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    Any opinions as to why adding/removing Sleeve Balun to my CoCo did not make any significant difference?

  9. #1219
    First officer 1090 MHz's Avatar
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    I think your can is just way too big in diameter. From what I've seen the sleeve baluns are typically twice the size of the cable... so a 1/4 inch hardline will have a 1/2 inch sleeve that's a 1/4 wave in length.

    http://www.antenna-theory.com/definitions/bazooka.php

    I'm actually working on my new antenna and it's sleeve balun is the last thing I need to do tonight. I have everything ready including N connectors for the 1/4 inch helix.

  10. #1220
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    Quote Originally Posted by 1090 MHz View Post
    I think your can is just way too big in diameter. From what I've seen the sleeve baluns are typically twice the size of the cable... so a 1/4 inch hardline will have a 1/2 inch sleeve that's a 1/4 wave in length.

    http://www.antenna-theory.com/definitions/bazooka.php

    I'm actually working on my new antenna and it's sleeve balun is the last thing I need to do tonight. I have everything ready including N connectors for the 1/4 inch helix.
    Thanks for your advise about too large dia of sleeve. Actually I did not mind big dia sleeve due to the following quote from ARRL Antenna Book:
    "The diameter of the coaxial detuning sleeve should be fairly large compared with the diameter of the cable it surrounds. A diameter of two inches or so is satisfactory with half-inch cable."

    The above quote discourages small diameters, but does not put an upper limit on dia of sleeve.

    As far as I know, the smaller dia is discouraged because of outer jacket of coax. if a sleeve is tight fitting to the cable, the entire space between sleeve & cable shield is filled with cable jacket. This will require that the length of sleeve is calculated using Velocity Factor of cable Jacket. Also, jacket material being much more lossy than the core insulating material, antenna efficiency will go down. For this reason it is preferred to have a large dia sleeve, so that almost entire insulation between sleeve & braid is air.

    I used Pepsi can as it is very handy. It is made of soft aluminum, and hence easy to cut and drill hole in center. Since my coaxial braid is non-solderable type, using Pepsi can with F-Male to F-Male adapter was the easy solution.

    Anyway, I will make another sleeve with a smaller dia can. I don't want to use cans made of iron sheets as it is a magnetic material. I cannot use aluminum tube either as I cannot solder an aluminum disk to the the aluminum tube. My only option is to find an aluminum can of smaller diameter. Till then the project is on hold....
    Last edited by abcd567; 2014-06-08 at 10:07.

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