How does antenna transmit a signal?

Replies

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  ankitchrungu

  the antenna is connected to a transmitter which is designed to output a voltage as a function of time. this voltage is an e.m.f. that forces free charge in the conductive element of the transmitting antenna to slosh back and forth along the element. in the receiving antenna, there is free charge in the conductive element that are affected (because like-signed charges repel and unlike-signed charges attrack) by the movement of charge that is happening in the transmitting antenna. because of the usual large distance between the transmitting antenna and the receiving antenna, that movement of charge in the receiving antenna is minute, much smaller than the quantity of charge and movement in the transmitting antenna. but that is what receivers and RF amplifiers are for; making that small movement of charge control a much larger movement of charge (that eventually finds its way to your radio loudspeakers).
  
  so you have the motion of charge at one location affecting the movement of charge at another location. since the reaction of charge in the receiving antenna is not an instantaneous reaction (from the POV of an observer that is equal distant between the two antennae), what is it that is in between the two antennae that, after a finite period of time, forces the charge in the receiving antenna to move?
• 

  just2rock

  antenna transmit signal over Radio frequency spectrum.Closing to certain guidlines you have to set while manipulating them.Voltage transmit happens to be over the specific coil readius of the antenna,suppose Yagi Uda antenna ,the insulated copper coil has specific voltage transmission rate .If you start manipulating same will be noticeable.
• 

  silenthorde

  Hi,
  
  an antenna is simply a piece of conductor as you said. As we know that when current flows through a conductor, a magnetic filed is produced. This magnetic field is what we utilize in our antennas. So at the transmitter electromagnetic filed is produced by passing current through the conductor.
  
  At the receiver the antenna works in just the reverse manner. The time varying electromagnetic field induces a voltage across the antenna according to Faraday's law of induction.
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  elavarasan

  for example consider a dipole (two wire seperated by a small distance let it be wire(1) and wire(2)) and if u apply sinusoid voltage to it (ie phase to wire(1) and ground to wire(2)).At one fourth of the time period the voltage will be maximum so that one wire will be at maximum voltage or potential and so that the electric field lines will emerge from that wire(1) to the other wire(2) that is in lower potential.and at three fourth of wavelenght of the input sine voltage the voltage value is negative so the wire(2) will be more positive than wire(1) so that electric field lines will flow from wire(2)to wire (1) .
  ->now if u can visualize from the starting of the sine signal to its full period the electric field will also forms a circular loop (ie half of the loop is formed during wire(1) in +ve potential and next half of the loop is formed during wire(2) in +ve potential
  and as this electric field disturbance forms the closed loop it can propagate in free space without any medium
  this is the mechanism of antenna
• 

  elavarasan

  The electric field lines will emerge from the wire as bubble smoke from a experienced smoker or u might have seen the smoking sequence in any program in cartoon network
  
  and this is the mechanism only for dipole antenna and it is basic of radiation