Need of Modulation

Size of Antenna

Signals are transmitted via EM waves. EM waves are transmitted by using an antenna. What will be the size of antenna?

Antena height must be multiple of λ/4 .

Where λ = c/f. λ is inversely proportional to frequency.

λ = c/f = 300000000/3000 = 100000 =100Km

Antena height = λ/4 = 100000/4 = 25000= 25Km

Radiated Power

P = 1/ λ2

λ = c/f

P = 1/ (c/f)2
P = f 2 / c 2

  • To minimize the interference from other signals.(commercial FM stations transmits voice without any interference).
  • High frequency carrier travel a greater distance.Low frequency signal carries low energy.
  • Multiplexing is possible.Multiple signals can use same medium.

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