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B LED in dipole antenna

  1. Mar 13, 2017 #1
    Hi.

    In this video around 6:45, this guy builds a simple dipole antenna with an LED and capacitor in parallel in the center. The LED flickers when close to a transmitting cellphone.

    Since the LED only lets current pass in one direction, shouldn't this quickly lead to a charge imbalance between the parts of the antenna and thus create an opposing field so the LED should stop working after a while?
     
  2. jcsd
  3. Mar 13, 2017 #2

    Baluncore

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    Current will also flow in the reverse direction once the reverse breakdown voltage is reached. Usually about 6V. The LED will be destroyed by reverse current if too much current flows.
     
  4. Mar 17, 2017 #3
    This is not a LED.

    upload_2017-3-17_7-5-20.png
     
  5. Mar 17, 2017 #4
    Yes, but he only uses this lamp in the first experiment. In the second part of the video he clearly uses an LED. The label can be seen at 7:08.
     
  6. Mar 17, 2017 #5

    davenn

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    Gold Member

    yes agreed
    I have issues with that it is supposed to be a capacitor in parallel with the LED, ceramic Capacitors DONT have black band on one end of them
    BUT there are plenty of diodes that are blue bodied and have black bands on one end ... a capacitor in there just doesn't make sense

    it's a pity that the video isn't in English so that the narration could be understood !!

    This would be a more logical setup
    the LED conducts 1/2 the cycle, the diode conducts the other 1/2 cycle so there is no build-up of charge at one end

    and that situation I have often used as a RF detector ... works very well

    upload_2017-3-18_11-3-18.png

    cheers
    Dave
     
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