I heard that an antenna converts a RF electrical signal into a EM wave?

Question

first of all i dint understand the nature of RF signal ie how it can be generated?how it looks like?i also heard that it has some frequency?

how is it possible?

Answer 1

RF stands for Radio Frequency. It is NOT an ElectroMagnetic wave.

(http://www.tonex.com/Courses/511/)

They range from 3 Hz to 300 GHz (http://en.wikipedia.org/wiki/Radio_frequ...

Answer 2

Needless to say, EMR - electromagnetic radiation, or the transmisson of electomatic energy (also know as RF) through air and space is a complex subject that requires more than a few sentences to explain.

When current flows through any wire conductor, an electric and magnetic field is created around the wire.  Transformers work on the principle of an alternating magnetic field around one wire (or many turns of wire) inducing current and voltage into another wire in close proximity.  In essence a transformer is transfering, through space, voltage and current from one wire to another wire.  But the wires in a transformer must be in very close proximity to each other to effeciently transfer energy from one wire to the other.  Power transformers operate at a very low frequency of around 60 Hz. (the signal changes polarity 60 times per second)

Antennas also transfer electrical energy from one wire, or conductor to another.  But antennas "radiate" their electrical energy through air and space.  Antennas can only effeciently radiate electromatic energy into air and space when operating at higer frequencies.  At high frequencies, EMR easily escapes the wires and readily travels through space.  Wires start becoming good EMR radiators beginning around 100 KHz (kilo Hertz or thousands of alternating cycles) and on up into many GHz (giga Hertz, or billions of alternating polarity cycles per second) and beyond.

For most effective radiation of EMR, transmitting antennas must be "tuned", or "resonant" to the frequency of primary interest.  At resonance an antenna radiates the maximum amount of electrical energy into space.

As well, to effeciently receive EMR, the receiving antenna must resonate to the same frequency as the transmitting antenna.  In this case, a receiving antenna (just like a secondary winding of a transformer) will absorb radiation from the signals in the air, convert these signals back into electrical signals and carry these signals from the antenna to the receiving device.  The receiver then detects, decodes, and processes the signal for further use.

Answer 3

Yes, Adam, that is correct: an antenna generates EM based on RF.

The RF is electric "pulses" in circuits. When the pulses travel along the antenna, they generate EM waves.

How and why: think about a radio station.  They play music, and their equipment has circuits that generate electricc pulses that "carry" the music. Those pulses eventually reach the antenna, where they cause EM waves.  Those waves reach the antenna in your car radio.  The car radio has circuits that translate the EM waves into electrical pulses, that drive the speakers, so you hear the music.

HTH