Explain why high frequency carrier waves are needed for effective transmission of signals?

@ IMPRACTICAL LENGHT OF ANTENNA :

  For the effective transmission of an EM wave the lenght of the antenna should be comparable with the wavelenght of the wave. The minimum lenght required for the antenna is l = wavelenhght/4. For a small frequency signal we need to use a very high antenna which is impractical.

@ LOW OPERATING RANGE :

  For low frequency signals the energy of radiation is low. [Power radiated is proportional to (l/wavelenght)raised to 2 ] So it is attenuated with in short distance.

@ OVERLAPPING OF DIFFERENT CHANNELS:

  If low frequency signals are transmitted simultaneously from diff transmitting stations there will be overlapping and intererence between signals. All will mixed up & there will be no way to distinguish them.

  FOR THESE REASONS FOR LONG DISTANCE AND EFFECTIVE TRANSMISSION MODULATION[high frequency carrier wave ] IS NECESSARY.