Modulation in general sense is the mixing of two signals. In the communication system modulation is the process of varying some characteristics of carrier wave (Amplitude, phase or frequency) with respect to the modulating wave (message signal). In other words modulation process is viewed as the frequency transformation of message signal from low frequency to high frequency band. The impression can be performed by varying the amplitude, frequency or phase of the carrier signal in accordance with the rate of change of the low frequency signal. The low frequency signal, usually the information bearing signal is called modulating signal.
Need of Modulation or Benefit of Modulation :
Modulation is needed due to following reasons
Practical Antenna length
Mixing up of different voice signals
Unpredictable variation in volume and pitch of voice signal
Practical Antenna Length : The voice frequencies in the band of 20HZ to 20KHZ, For the efficient transmission and reception of radio frequency signals. The antenna length ‘l’ required in terms of wavelength ‘^’ used in transmission is expressed as ‘^’ = c/f.
Where c = velocity of light in free space
F = frequency of wave used in transmission
L = length
L = ^/2,which is very high for the frequency range of 20 HZ to 20KHZ and length of antenna is impractical to construct.
We know that in case of free space is used as a transmitting medium (i.e. channel), messages are transmitted and received with the help of antennas. For efficient radiation and reception the transmitting and receiving antennas must have lengths comparable to a quarter-wavelength of the frequency used. Obviously, it will be totally impracticable to construct and install an antenna of such a height. However, this height of the antenna may be reduced by modulation technique and yet effective radiation and reception is achieved. In modulation process, low frequency of audio signal at radio stations are translated to higher frequency spectrum i.e., radio frequency range. These higher radio frequencies with the small wavelength act as carrier for the audio frequencies (i.e. modulation signal).Thus, the height of the antenna required is much reduced and becomes practical.
Mixing up of different voice signals : All the voice signals (Audible sound wave) is concentrated with in range of 20 Hz to 20KHZ, so that all signals from the different sources would be hopelessly and inseparateably mixed up if they are transmitted without modulation. The modulation helps to separate then in radio frequency spectrum.
Unpredictable variation in volume and pitch of voice signal : The unmodulated carrier wave doesnot transmit any message or intelligence because they have constant amplitude frequency and phase. The voice signal has unpredictable variation in volume and pitch (amplitude and phase) which is impossible to represent these two variables by a set of three constant parameters (amplitude frequency and phase). Thus the message contains in voice is transmitted by varying any one parameter (amplitude frequency and phase) of carrier. According to the variation in the message signal.
Types of Modulation
Modulation is basically of two types:
i. Continuous Wave Modulation : When the carrier wave is continuous in nature, the modulation process is known as continuous wave (CW) modulation or analog modulation. Examples of continuous wave modulation are Amplitude Modulation and Angle Modulation. When the amplitude of the carrier is varied in accordance with the message signal, it is known as amplitude modulation (AM). Also, when the carrier is varied according to the instantaneous value of the modulating signal, it is called angle modulation. Angle modulation may be further subdivided into Frequency Modulation (FM) and Phase Modulation (PM), in which the instantaneous frequency and phase of the carrier, respectively, are varied in accordance with the message signal.
ii. Pulse Modulation : When the carrier wave is a pulse-type waveform, the modulation process is known as pulse modulation. In pulse modulation, the carrier consists of a periodic sequence of rectangular pulses. Pulse modulation can be of an analog or digital type.
In analog pulse modulation, the amplitude, duration or position of a pulse is varied in accordance with sample values of the message signal. The analog pulse modulation may be of following three types: a. Pulse-amplitude modulation (PAM). b. Pulse-duration modulation (PDM).
c. Pulse-position modulation (PPM).
On the other hand, the digital form of pulse modulation is known as Pulse-code modulation (PCM).
Need of Modulation or Benefit of Modulation :
Modulation is needed due to following reasons
Practical Antenna length
Mixing up of different voice signals
Unpredictable variation in volume and pitch of voice signal
Practical Antenna Length : The voice frequencies in the band of 20HZ to 20KHZ, For the efficient transmission and reception of radio frequency signals. The antenna length ‘l’ required in terms of wavelength ‘^’ used in transmission is expressed as ‘^’ = c/f.
Where c = velocity of light in free space
F = frequency of wave used in transmission
L = length
L = ^/2,which is very high for the frequency range of 20 HZ to 20KHZ and length of antenna is impractical to construct.
We know that in case of free space is used as a transmitting medium (i.e. channel), messages are transmitted and received with the help of antennas. For efficient radiation and reception the transmitting and receiving antennas must have lengths comparable to a quarter-wavelength of the frequency used. Obviously, it will be totally impracticable to construct and install an antenna of such a height. However, this height of the antenna may be reduced by modulation technique and yet effective radiation and reception is achieved. In modulation process, low frequency of audio signal at radio stations are translated to higher frequency spectrum i.e., radio frequency range. These higher radio frequencies with the small wavelength act as carrier for the audio frequencies (i.e. modulation signal).Thus, the height of the antenna required is much reduced and becomes practical.
Mixing up of different voice signals : All the voice signals (Audible sound wave) is concentrated with in range of 20 Hz to 20KHZ, so that all signals from the different sources would be hopelessly and inseparateably mixed up if they are transmitted without modulation. The modulation helps to separate then in radio frequency spectrum.
Unpredictable variation in volume and pitch of voice signal : The unmodulated carrier wave doesnot transmit any message or intelligence because they have constant amplitude frequency and phase. The voice signal has unpredictable variation in volume and pitch (amplitude and phase) which is impossible to represent these two variables by a set of three constant parameters (amplitude frequency and phase). Thus the message contains in voice is transmitted by varying any one parameter (amplitude frequency and phase) of carrier. According to the variation in the message signal.
Types of Modulation
Modulation is basically of two types:
i. Continuous Wave Modulation : When the carrier wave is continuous in nature, the modulation process is known as continuous wave (CW) modulation or analog modulation. Examples of continuous wave modulation are Amplitude Modulation and Angle Modulation. When the amplitude of the carrier is varied in accordance with the message signal, it is known as amplitude modulation (AM). Also, when the carrier is varied according to the instantaneous value of the modulating signal, it is called angle modulation. Angle modulation may be further subdivided into Frequency Modulation (FM) and Phase Modulation (PM), in which the instantaneous frequency and phase of the carrier, respectively, are varied in accordance with the message signal.
ii. Pulse Modulation : When the carrier wave is a pulse-type waveform, the modulation process is known as pulse modulation. In pulse modulation, the carrier consists of a periodic sequence of rectangular pulses. Pulse modulation can be of an analog or digital type.
In analog pulse modulation, the amplitude, duration or position of a pulse is varied in accordance with sample values of the message signal. The analog pulse modulation may be of following three types: a. Pulse-amplitude modulation (PAM). b. Pulse-duration modulation (PDM).
c. Pulse-position modulation (PPM).
On the other hand, the digital form of pulse modulation is known as Pulse-code modulation (PCM).
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ReplyDeleteGood information. I recently bought a 4G Signal booster for improving my 4G signal strength.
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