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Electromagnetic signals questions

  1. Jan 4, 2006 #1
    Hi i am wondering in an electromagnetic signal how times bigger the electonic signal is bigger from the magnetic one...... I have also read that becuase the electric signal is bigger the most reveivers ignores the magnetic field and only searchs for the electric signal...

    Do u know any receiver that uses the magnetic component of an electromagnetic signal?
    Really how can we denote an electromagnetic signal?
  2. jcsd
  3. Jan 4, 2006 #2
    You aren't even close. The receiver doesn't 'look' for a certain part of the signal as you imply. The antenna creates an electric current which is the same as any other electric current. Of course the signal strength is very low. The receivers job is to filter out the frequency wanted and amplify it and convert it to audio which we can hear. The antenna will not work if either part of the electromagnetic signal is missing. In fact, you can't really have one without the other.
  4. Jan 5, 2006 #3
    Thx a lot but my book mentions that receivers use the electri part of the signal and not the magnetic one because the electric one is c times bigger E=c*B
  5. Jan 5, 2006 #4


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    Staff: Mentor

    But then a loop antenna would be 3*10^8 times less efficient than a dipole, and my simple AM broadcast radio receiver wouldn't work very well.....

    As supernova says, antennas couple to EM waves, where both the electric and magnetic fields are present in a travelling or stationary electromagnetic wave. If you want to talk about near-field capacitive or inductive pickups, then yes, you don't need an EM wave. But antenna equations are based on Maxwell's equations for electromagnetic waves, not for near-field coupling of one or the other field.
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