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Thread: best antenna

  1. #1221
    Captain abcd567's Avatar
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    @1090 Mhz

    Please visit http://www.w8ji.com/sleeve_baluns.htm

    The conclusion is at bottom of above page. I am copying below these paragraphs.

    From the above, we observe the following characteristics in a sleeve balun:
    1.) The highest possible choke sleeve impedance (largest ratio of balun sleeve diameter to outside of transmission line) is desired. We won’t have a good balun if the choking Zo (ratio of sleeve inner diameter to coaxial shield outer diameter) is small.

    2.) The balun requires the lowest possible loss over the length of the sleeve. It forms a transmission line from the inside of the sleeve to the outside of the coax. The coax jacket is a dielectric, so we need to keep a lot of air inside of the choking sleeve or the coax jacket will increase loss and reduce impedance, both being very undesirable.

    3.) The velocity factor of the sleeve, based on the dielectric between the sleeve and the shield of the coaxial cable we are trying to balance or choke, is very important to length of the sleeve.

    The following construction guidelines apply:
    The cable should have a good low-loss jacket or a very large air or low loss dielectric gap between the shield and the sleeve. Since energy is normally confined to the inside of a coaxial cable manufacturers are not concerned about jacket losses. They use outer materials with long life, not low RF loss. It is advisable to use a filler material with a high volume of air to maximize sleeve impedance and minimize sleeve losses.

    It is also advisable to use the largest practical diameter sleeve with the smallest diameter coaxial cable inside to maximize choking impedance.

    The sleeve length has to account for velocity factor of the sleeve, since the sleeve forms a coaxial transmission line with the outer conductor of the coaxial cable it is intended to choke or decouple.

  2. #1222
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    Quote Originally Posted by abcd567 View Post
    @1090 Mhz

    Please visit http://www.w8ji.com/sleeve_baluns.htm

    The conclusion is at bottom of above page. I am copying below these paragraphs.

    From the above, we observe the following characteristics in a sleeve balun:
    1.) The highest possible choke sleeve impedance (largest ratio of balun sleeve diameter to outside of transmission line) is desired. We won’t have a good balun if the choking Zo (ratio of sleeve inner diameter to coaxial shield outer diameter) is small.
    .
    I would agree, this is the type of advice I have been seeing in books etc, also it is important to keep the sleeve as concentric as possible to avoid uneven current flow.
    If you take the diameter to the extreme then you end up with something resembling the alternative design that has either 4 quarter wave stubs at right angles to the co-ax or a quarter wave disk, electrically these serve the same purpose, just visualise folding the stubs or disk up into a cylinder.
    Just out of interest I wonder what the result would be of a sleeve with a radius of 1/4 wave and hight the same, then you would have both the sleeve and effectively the quarter wave stubs.
    Ben.
    FR24 F-EGLF1, Blitzortung station 878, OGN Aldersht2, PilotAware PWAldersht, PlanePlotter M7.

  3. #1223
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    Quote Originally Posted by F-EGLF1 View Post
    ......Just out of interest I wonder what the result would be of a sleeve with a radius of 1/4 wave and hight the same, then you would have both the sleeve and effectively the quarter wave stubs.
    Ben.
    Have you seen my sleeve's photos in my post # 1230? The Pepsi can I used as sleeve was cut to a length of 69 mm & has dia of 65 mm, so radius is very close to 1/8 λ. We need a can of double the dia of Pepsi can to get a radius of 69 mm i.e. 1/4 λ.

  4. #1224
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    Another Experiment: A 1/2 λ sleeve dipole
    After Failed experiment of Sleeved CoCo, I decided to utilize the Pepsi sleeve for another experiment: A 1/2 λ sleeve dipole. The Pepsi can is the down 1/4 λ limb of the dipole, and upper limb is a whip made out of core of coaxial cable 69 mm long (with insulation) + 20 mm bare conductor for insertion into the connector.

    The Pepsi can serves dual purpose:
    (1) Lower limb of the dipole &
    (2) Decoupling Sleeve


    Please see below:
    (1) Three hrs trial run VRS coverage screenshot.
    (2) 4 photos, showing construction details.

    Image 1 of 6 : VRS Coverage
    The range rings are 50 kms apart, the outermost blue ring is 450 kms from the receiver.




    Image 2 of 6 : Construction Details 1



    Image 3 of 6 : Construction Details 2



    Image 4 of 6 : Construction Details 3


    Image 5 of 6 : Fully Assembled


    Image 6 of 6: Sketch of Pepsi Can Dimensions


    Edited on Sept 01, 2015 to restore broken link to image 2 of 6
    Last edited by abcd567; 2015-09-01 at 19:50.

  5. #1225
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    .
    Test Setup for 1/2 λ Sleeve Dipole

    Picture 1 of 2



    Picture 2 of 2

  6. #1226
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    Have you ever seen what is inside a rubber ducky antenna? A Sleeve Dipole

    http://martybugs.net/wireless/rubberducky.cgi


  7. #1227
    First officer 1090 MHz's Avatar
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    As you know I'm modding a high gain WiFi omni antenna. It incorporated an internal 1/2 inch sleeve balun and 1/4 inch brass elements. Here are 2 WiFi antennas.. the bottom one is the one that is getting modded to become a high gain 8.5 element 1090MHz antenna. http://ads-b.ca/wifi/img_9602.htm

    Take also into consideration the possibility that the aluminum pipe that is part of the antennas mount might also act as a sleeve balun too: http://ads-b.ca/antenna-build/img_9610.htm

    The new antenna coco is made from 1/4 inch LDF1-50 hard line which is very close to the 1/4 brass tubing the WiFi antenna used. http://ads-b.ca/LDF1-50/coco/
    The 1/2 inch brass sleeve balun was extended using copper water pipe. The brass and copper soldered together very nicely. It's a tight fit in the fiberglass tubing.

    The new antenna will also be wired with LDF1-50 from antenna, down the tower, to the radio. I'm thinking of also installing a ferrite choke on the LDF1-50 just below the N connector. This will be inside the aluminum mounting pipe where it's kept dry.

  8. #1228
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    Quote Originally Posted by 1090 MHz View Post
    As you know I'm modding a high gain WiFi omni antenna. It incorporated an internal 1/2 inch sleeve balun and 1/4 inch brass elements. Here are 2 WiFi antennas.. the bottom one is the one that is getting modded to become a high gain 8.5 element 1090MHz antenna. http://ads-b.ca/wifi/img_9602.htm

    Take also into consideration the possibility that the aluminum pipe that is part of the antennas mount might also act as a sleeve balun too: http://ads-b.ca/antenna-build/img_9610.htm

    The new antenna coco is made from 1/4 inch LDF1-50 hard line which is very close to the 1/4 brass tubing the WiFi antenna used. http://ads-b.ca/LDF1-50/coco/
    The 1/2 inch brass sleeve balun was extended using copper water pipe. The brass and copper soldered together very nicely. It's a tight fit in the fiberglass tubing.

    The new antenna will also be wired with LDF1-50 from antenna, down the tower, to the radio. I'm thinking of also installing a ferrite choke on the LDF1-50 just below the N connector. This will be inside the aluminum mounting pipe where it's kept dry.
    Thanks for the update. The new LDF1-50 antenna looks sturdier than the old brass tube one. Adding ferrite choke is a good idea.

  9. #1229
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    Quote Originally Posted by abcd567 View Post
    Thanks for the update. The new LDF1-50 antenna looks sturdier than the old brass tube one. Adding ferrite choke is a good idea.
    According to the ARRL handbook ferrite chokes are only of any use at frequencies below 144MHz (Section 15.1.4) this is due to the ferrite material responding differently at higher frequencies.
    Ben.
    Last edited by F-EGLF1; 2014-06-09 at 05:24. Reason: Added page ref
    FR24 F-EGLF1, Blitzortung station 878, OGN Aldersht2, PilotAware PWAldersht, PlanePlotter M7.

  10. #1230
    First officer 1090 MHz's Avatar
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    Ferrite chokes are actually good for frequencies up to around 1000 MHz. It all depends of what type of material the ferrite bead is made from.

    Ferrite beads are used for RF decoupling and parasitic suppression. When placed over a coaxial cable they prevent RF from flowing on the outside of the shield but do not affect the signal inside the cable.

    For RFI use,
    Mix 31 is effective from 1-500 Mhz,
    Mix 43 works from 20-250 Mhz,
    Mix 61 is for 200-1000 Mhz
    Mix 77 favors .5-20 MHz.

    http://palomar-engineers.com/ferrite.../ferrite-beads

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