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Thread: signal cancels in perpendicular transmitting antennas

  1. #1 signal cancels in perpendicular transmitting antennas 
    N+
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    hi all
    pls can anybody confirm this knowledge that i remember from school
    and help me with little explanation pls ty:

    "signal cancels in perpendicular transmitting antennas"

    the case that i remember was this or something similar
    ty


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  3. #2  
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    I am no expert in antennas so please accept what I write with appropriate caution.

    I see no reason why signals from perpendicular antennas should cancel each other out. The signals would not be polarized in the same direction so interference is unlikely. Also, if the signals did cancel out in all directions, one would feel compelled to ask what has happened to the power transmitted by each antenna? Generally. destructive interference is accompanied by constructive interference somewhere else.


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  4. #3 Re: signal cancels in perpendicular transmitting antennas 
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    Quote Originally Posted by N+
    hi all
    pls can anybody confirm this knowledge that i remember from school
    and help me with little explanation pls ty:

    "signal cancels in perpendicular transmitting antennas"

    the case that i remember was this or something similar
    ty
    I saw the next fellows post and now I believe I understand the question.

    To some extent you will get a blocking of the signal, if they are simultaneous transmissions. The reason is that electrons flow from an abundance to a shortage of electrons.

    The antenna is actually made short of electrons by the power line feeding it. In turn an ARC (Anode Rectified Cathode) ray is created on the surface of the antenna. This area is abundant with electrons. It is the exact same principle used in a mercury rectifier.
    The mercury is short of electrons in the pool, yet above the mercury at the surface is created an abundance of electrons. That flows through wire and back to the pool of mercury.

    The point is that when you aim two antennas at each other. The signal that would have passed the other antenna. Is blocked, as if an insulator was placed between the antenna and the rest of the world.

    Now there are situations and exceptions. If you create an area between the antennas that is high enough in voltage. That area could transmit around and through the world.

    My answer would be yes in most casual transmissions. There could be an area blocked by the signal that would have been transmitted to.

    No in higher powered or special situations.


    Sincerely,


    William McCormick
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  5. #4  
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    Is this in the far-field or near field? Is it an ideal antenna, or does the wire have a radius? These things are needed to answer your question.
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  6. #5 Perpendicular transmitting antennea 
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    In the case of two perpendicular transmitting antennae, assuming they are transmitting the same frequency, there can be areas of cancellation.

    If antenna 1 and antenna 2 are placed 1/2 wavelength apart and transmit in phase with one another, then they will cancel in the exact centre of the two antennae.

    This is not to say that all that energy being transmitted just goes away!
    It just means that the radiation pattern is distorted from the normal circular shape.
    Viewed from above (with radio sensitive goggles of course the emission pattern would resemble a figure eight, with two extended lobes of radiation away from the centre of the two antennae.

    This technique is actually used in real transmission towers to shape the transmission so that the most power is directed to the desired region, and little is wasted on regions the broadcaster is not interested in.
    In real applications, the arrangement of multiple antennae elements can be numerous and quite complex, with the phase of the signal delivered to each element also tightly controlled.

    The ultimate expression of this principle is the "steerable radar antenna" where very many transmitting element in a precise array are fed signals with phases specifically designed to "steer" the power lobe(s) exactly where the operator desires over many degrees of the compass.

    There is some very impressive kit out there, indeed, I just wish I really did have some radio sensitive goggles.
    --
    There is that which is known.That which is known to be Unknown. The unknown that is unknown to be unknown... and that which is thought to be known, but is actually unknown.
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