MODULATION

Modulation is a process of superimposing Audio Frequency(A.F) over Radio Frequency(R.F) or carrier wave in the transmitter.

The need for modulation is

1. To avoid construction of impractical length of antenna which would even then would not be sufficient enough for communications over long range.

2. A.F. band is 20 Hz to 20KHz which is a bandwidth of 19.88 KHz and hence very few channels can be accommodated.

3. Very high power would be required to transmit such low frequencies for them to travel over long distances.

   
   

The advantages are:

1. R.F. has higher frequencies which require shorter antenna

2. R.F. spectrum has very large bandwidth which can accommodate a large number of channels

3. Transmission power would be very less due to high frequencies.

The 2 types of Modulation in Analogue Radio communications are

1. Amplitude Modulation

2. Angle Modulation

   • Frequency Modulation

   • Phase Modulation : Phase of carrier wave is modulated after fixed intervals. (Used in GPS)

The other type of Modulations are:

• Pulse Modulation – In this type of Modulation, the R.F. carrier pulses are modulated (not sinusodial) depending upon the amplitude of the modulating wave.

• Pulse Amplitude Modulation

  • Pulse Width Modulation

  • Pulse Position Modulation

  • Pulse Code Modulation