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Voltage the wave form is a sin or a triangle in a dipole antenna

  1. Aug 25, 2004 #1

    If my input voltage the wave form is a sin or a triangle in a dipole antenna, what is the difference between these two wave forms?


  2. jcsd
  3. Aug 25, 2004 #2
    ? ? Huh ? ?
  4. Aug 26, 2004 #3
    What is the problem? Is my problem make sense?

  5. Aug 26, 2004 #4


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    Mica, I think there is a language barrier.

    Can you explain your problem in a little more detail, please?
  6. Aug 26, 2004 #5
    I have a dipole antenna, my problem is the input source ( ex : a batterie) which energize the antenna, I think. And this input source I can generated a triangle wave form, I'm right? Like a generator which can generated sin, square, triangle wave forms etc. So, my question is if I put one of these kind of wave forms, what is the different on the output of the antenna (gain, radiation pattern, output energie, etc.)? Well, in my understanding I think the wave form of the input source in a sin wave form, I'm right?

    Thanks for the response,

  7. Aug 26, 2004 #6
    Still not following this. You talk about energizing the antenna with a battery. Doesn't make sense. Maybe you are just energizing your sine/triangle generator with battery. I don't know.

    Then you are questioning what the gain, radiation and such will be. That I understand.

    Then you mention you think the waveform on the input source is a sine wave. Well I imagine it would be whatever you drive the antenna with. Which is your choice.

    Now do you see why I said 'huh'? Please elaborate. I think if I understand the question I can help you.
  8. Aug 27, 2004 #7
    O.K. I explain what I understand in antenna. First, an antenna is a open circuit, right? So, to drive an antenna, you need an input source (voltage)which gives the antenna to radiated. Roughly speaking, the whole system is composed a generator and an antenna, right? The output of the generator can be a triangle,square, sin wave form ( like an impluse) ? So, this output is the input to the antenna right? If the output of the generator has a sin, triangle or square wave form then what are the consequences to the antenna? Is this make sense?

    Hope this explaination can clarify my problem, thanks again,

  9. Aug 28, 2004 #8
    An antenna is NOT an open circuit. The job of the antenna is to absorb power from the source and radiate it into space. Think about this: If the antenna is to absorb power it has to have an input impedance. Power cannot be transferred into an open circuit. It can be proven with ohms law.

    An antenna will have a fixed impedance at the frequency it is designed for. At other frequencies it will behave differently. At the design frequency the antenna should appear resistive. It is a resonant circuit. As you move in one direction it will appear inductive and the other direction appear capacitive. You will find it may also be resonant at certain harmonics of the design frequency but it may not have the same impedance.

    Common impedances for antennas can vary. 50 and 70 ohms is common. 300 ohms has been used. You will notice on some antennas that the feedline would appear to have a direct short placed across the feedline. This is an advantage since it is impossible for a static charge from wind to build up between the conductors of the feedline. However, at the design frequency of the antenna the impedance will NOT be zero.

    When harmonics are fed into the antenna the radiation pattern can change as well. You can find books written about this as well as every other thing I have stated here.

    Now onto your question about different waveforms going into the antenna.

    A square wave contains the fundamental frequency and all of the ODD harmonics out to (theororetically) infinity. So what you would have is an antenna radiating harmonics in different directions. Some more efficiently than others.

    A triangle wave contains the fundamental and ALL harmonics out to (theororetically) infinity. So the antenna would behave similarly to the square wave example except that would be radiating even more signals.
  10. Aug 28, 2004 #9


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    Think about it. A triangle or square wave can be made by adding up sine wave. For square wave, I think, all the odd harmonics and for a triangle wave all the even harmonics.

    For the antenna to radiate (output) all the input energy, the wavelength must match the length of the dipole. When you use a triangle input, the harmonics will decrease the output by reflecting back to the source causing deconstructive interference.


  11. Aug 28, 2004 #10
    dlgoff you mention that the harmonics will be reflected back to the source and cause deconstructive interference. This is true but the fundamental will still radiate the same power. I'm not sure if you implied this or not. Some harmonics will radiate better than others.
  12. Aug 30, 2004 #11


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    Mica - I'm not sure I understand your question. I think what you want to do is to use your triangular, sine, square, wave... to modulate ( frequency, phase, amplitude, modulation) a much higher frequency carrier wave.
  13. Aug 30, 2004 #12
    Thanks for all the information. Now, it clarify a little better for me. Thanks for this open forum, it helps me a lot and I can find answer that I don't need to run around and end up with nothing. I need a good book for starter in understanding Antenna. I need a book which has a lot for examples, any suggestions? I have a book in Antenna Theory and Design but this is not I'm looking for. I want is something like case study, from the input to the output of the antenna. Does exist a book like this?

    Thanks again the precious information,
  14. Aug 30, 2004 #13
    Research antenna books concerning amateur radio.
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