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Why Antennas Have Ground Plane?

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  • EA1DDO
    replied
    I agree that.

    Cheers

    Leave a comment:


  • Stealth
    replied
    Originally posted by EA1DDO View Post
    I said that because talking about ground someone could be confused with ground reflections, or ground gain, or any other ground effect.
    Those affects, as you know, are happening to any terrestrial antenna.
    There is more likelihood that people will be confused by your ideas than are helped. This is a forum for aircraft tracking enthusiasts that in most cases have limited radio theory knowledge.

    Leave a comment:


  • EA1DDO
    replied
    I said that because talking about ground someone could be confused with ground reflections, or ground gain, or any other ground effect.
    Those affects, as you know, are happening to any terrestrial antenna.

    Leave a comment:


  • Stealth
    replied
    Nothing wrong about the use of the term ground plane and I don't know why you suggest that it is in some way an old term, radials are merely the means by which that effect is obtained. 'Radials' by itself has no meaning.

    Leave a comment:


  • EA1DDO
    replied
    Basically, "Ground plane" is an old denomination. I think radials is more appropriated.
    As abcd567 said, radials are part of the antenna, half side of the antenna.
    In the 1/4 vertical model, radials are affecting to impedance and to the lobules.
    In a 1/4 vertical, 50 OHm are achieved with radials around 45.

    Cheers
    Maximo

    Leave a comment:


  • abcd567
    replied
    Originally posted by Flieger28 View Post
    as the 2m SMA Cable has 50 Ohm, i guess it would be clever if i choose the Coax, from which i build the antenna, with the same 50 Ohm?
    1. You can use the 50 ohm cable to make this antenna if you want.

    2. This antenna has 4 horizontal radials. It is meant to demostrate the importance of a ground plane. Same construction with 8 slanting radials gives much better performance. It is given here:

      Quick Spider
    Last edited by abcd567; 2018-02-24, 17:09.

    Leave a comment:


  • Stealth
    replied
    Originally posted by Flieger28 View Post
    Found this thread and this Antenna looks reasonably simple to build. But i have a few questions. I have a orange Flightaware Dongle which has an SMA Connector.
    X snip....

    as the 2m SMA Cable has 50 Ohm, i guess it would be clever if i choose the Coax, from which i build the antenna, with the same 50 Ohm?
    If you have suitable 50 ohm cable (with solid centre wire) then just use that and fit a SMA plug for your dongle.

    Leave a comment:


  • Flieger28
    replied
    Found this thread and this Antenna looks reasonably simple to build. But i have a few questions. I have a orange Flightaware Dongle which has an SMA Connector.
    So i guess i need this things to start

    F-Connector
    F-Stecker.jpg

    F to SMA
    F-SMA.JPG

    SMA-SMA to the Stick
    sma.jpg

    as the 2m SMA Cable has 50 Ohm, i guess it would be clever if i choose the Coax, from which i build the antenna, with the same 50 Ohm?

    Leave a comment:


  • abcd567
    replied
    Not ALL antennas need ground plane. Examples are J pole and CoCo.

    As far as commercial antennas as concerened, if groundplane is needed, then it is built and supplied with antenna. If no ground plane is built/supplied with antenna, it does not need ground plane.

    A large number of people use Flightaware antenna, and have installed it on a metallic pipe support, on tower/mast, and on non-metallic pipe support. To my knowledge, no one mentioned any affect of type of support on the antenna.performance.

    Leave a comment:


  • RockRidge
    replied
    Does the mounting of the antenna act like a ground plane / dipole?
    If I understand it correctly, the coax shield is connected to most mounting hardware.
    Disregarding lighting protection for this discussion, if you had a nonmetallic mounting pole as opposed to a metal pole, would it change the results?
    If you are connected to a wide tower like a windmill vs a pole would it change?
    How anyone added a ground plane to the FlightAware 1090MHz ADS-B 26 inch Antenna http://a.co/dPCBhai
    I have so much to learn!

    See also https://forum.flightradar24.com/thre...-Ground-Planes

    Leave a comment:


  • abcd567
    replied
    A monopole antenna is half of a dipole antenna placed over a ground plane.



    If the ground plane is perfectly conducting, the monopole antenna shown in Fig (a) will be equivalent to a half wave dipole shown in Fig (b) taking image into account.







    A monopole sitting above a metallic ground plane acts as a dipole above the metallic plane due to reflections.
    The monopole antenna has the same radiation pattern over perfect ground as a dipole in free space with twice the voltage.

    Last edited by abcd567; 2016-09-20, 18:18.

    Leave a comment:


  • G8VXY
    replied
    Not all antennas have ground plane, take the basic dipole.


    the received signal, think of it not so much as voltage but more currant, and best first describe the Dipole as half of it being a 1/4 wave and the other half being 1/4 wave 180 degrees out of phase so one is the opposite polarity to the other so currant flows from one half or the antenna to the other, ground plane work similar to the out of phase but they are not matched.

    Leave a comment:


  • abcd567
    replied
    @jcinbb
    Tin can antenna (Cantenna) performance is almost same as performance of slanting radial antenna (Spider).

    Leave a comment:


  • jcinnb
    replied
    I cannot thank you enough for the knowledge that you have shared. I have been into this for a couple of weeks, and, well, I just can't express my thanks adequately.

    I am making your tin can antenna. How do you think the graph of that one would compare?

    Leave a comment:


  • abcd567
    started a topic Why Antennas Have Ground Plane?

    Why Antennas Have Ground Plane?

    A Simple Experiment to Demonstrate How Ground Plane Radials Affect the Performance of An Antenna

    A 1/4 Wavelength Monopole Whip was tested under following conditions:
    (1) Only Whip, no ground plane radials.
    (2) Whip with horizontal ground plane radials.
    (3) Whip with 45 degrees slanting ground plane radials.

    The attached performance graphs show the importance & affect of ground plane radials.

    Image 1 of 5
    Device Under Test: 1/4 Wavelength Monopole, without & with radials





    Image 2 of 5
    Three Test Setups





    Images 3, 4, & 5 of 5
    Performance Graphs









    EDIT:
    The construction details of the Antenna Under Test are added below.


    All the 4 radials were inserted between the outer PVC jacket and the braid of the coax. The zip ties were used to secure the radials in position, as these have a tendency to move and change 90 degree angle with each other.

    After completion, I checked the continuity between the body of F-connector at other end of coax, and each of 4 radials by a multitester. All 4 were found electrically continuous, as the multitester beeped on each radial.

    The radials were inserted in the same way as a center wires of a Coco are inserted between the PVC jacket and braid of adjacent elements.

    Here is a larger size photo of the monopole with radials inserted and zip-tied.

    Last edited by abcd567; 2016-09-20, 17:09.
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