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Thread: Antenna (receiver,transmitter) questions... please help?

  1. #1 Antenna (receiver,transmitter) questions... please help? 
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    Hey forum!

    Can you please help me understand conceptually,

    O- How antenna receives and transmits a signal (and what causes one or the other effect (diffrence in use))
    O- (what defines a receiver / transmitter)
    O- How are vibrations tied into this..?
    O- How does the antenna shape affect the signal you can receive, transmit
    O- How is it that a company can sell or buy a frequency
    O- How are the frequencies used , is it a man made thing a range he can transmit in or is it an pre-existant earth phenomena that man is utilising.
    O- How does the transition between an image being taken then formed and sent out as a signal to be received happens?
    O- and what is the diffrences between wifi,radio,tv signals,


    (I apolagize if this sounds dull. i would like to just build a circuitry involving an antenna, but am confused over the theory behind it.
    i belive i would have much more higher ability to construct an efficient antenna if i knew the concepts behind how this whole thing works and how its utilized )

    Id appreciate your help guys!


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  3. #2  
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    Quote Originally Posted by Muto-kun View Post
    Hey forum!

    Can you please help me understand conceptually,

    O- How antenna receives and transmits a signal (and what causes one or the other effect (diffrence in use))
    Transmit: Current thrashes charge in the antenna. "You shake an electron, light comes out."
    Receive: Passing EM wave exerts forces on charges in antenna, making them move. That's the received current.

    (what defines a receiver / transmitter)
    You should be able to figure this out.

    How are vibrations tied into this..?
    See answer to first question.

    How does the antenna shape affect the signal you can receive, transmit
    How does a lens or mirror shape affect what you see/send?

    How is it that a company can sell or buy a frequency
    Not "a frequency," but "an interval of frequencies." And whether they can do it depends on the laws that prevail in a given locale.

    How are the frequencies used , is it a man made thing a range he can transmit in or is it an pre-existant earth phenomena that man is utilising.
    You can use either, but humans, by an overwhelming majority, use signals generated by humans.

    How does the transition between an image being taken then formed and sent out as a signal to be received happens?
    I don't know what you are asking. Are you asking how one transmits a picture? If so, all information can be represented by voltages (which, in turn, can represent bits). So the source of the information doesn't matter.
    and what is the diffrences between wifi,radio,tv signals,
    They differ in frequency and types of modulation used to impress the information onto the transmitted carrier wave.


    (I apolagize if this sounds dull. i would like to just build a circuitry involving an antenna, but am confused over the theory behind it.
    i belive i would have much more higher ability to construct an efficient antenna if i knew the concepts behind how this whole thing works and how its utilized )
    Id appreciate your help guys!
    Antenna theory is quite complex. If you're just building a project, you'd probably do well simply to consult one of any number of hobbyist publications on the subject. A good source is the ARRL. They have published many handbooks on the subject.


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  4. #3  
    Forum Cosmic Wizard
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    Some quick notes:

    Antennas provide an interface between free space and an electrical conductor/transmission line. They induce electric and magnetic fields in free space which then propagate outwards. (These same fields induce voltages and currents in receive antennas, allowing them to receive signals.)

    Transmitters transmit, receivers receive signals.

    Antenna shapes - basically you can transmit via H-fields (loop antennas) and E-fields (plate antennas.) Some do both (most antennas do this actually.) The dipole is a common differential antenna geometry, and the 1/4 wave monopole is a common single ended (+ground) geometry.

    The FCC manages who can use what frequency. They frequently have auctions to sell spectrum to the highest bidder.

    EM propagation is a natural phenomena that man is using to send information.

    Video images are first turned into a stream of information. This was formerly done by scanning the surface of a TV tube with an electron beam and turning the brightness into an RF signal. That signal was transmitted and reconstructed at the receiver.

    Wifi is a digital signal, modulated onto the 2.4GHz spectrum. It uses a form of modulation called complementary code keying. Radio and TV depend on the service. AM radio is the simplest. In that system, you choose a frequency, then send that frequency modulated by the audio. For example, take AM 880. This means you take an 880 khz sine wave and modulate it with the envelope of the audio. Then you transmit that 880 khz signal. At the receive side, you receive it, look at the envelope and turn that back into audio.
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  5. #4  
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    thank you, that helped a lot
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  6. #5  
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    could there be other geometric figures, that could transmit/receive signals..?
    and so if the received signal vibrates the receiver, then is there a purpose like making the antenna horizontal or vertical to receive the signal more fully..because it covers more of the receiving part?
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  7. #6  
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    Quote Originally Posted by Muto-kun View Post
    could there be other geometric figures, that could transmit/receive signals..?
    Of course. Antenna design is a huge field of study.
    and so if the received signal vibrates the receiver, then is there a purpose like making the antenna horizontal or vertical to receive the signal more fully..because it covers more of the receiving part?
    Some very general rules of thumb:
    -If your dipole antenna is equal to half your wavelength it will tend to be more efficient.
    -Far field EM waves have polarizations. If the antenna matches your polarization it will receive more efficiently. For example, you can have two antennas, one horizontal and one vertical, and transmit/receive two different polarizations.
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