The modulation process is required in a communication system to achieve the following basic needs
- Ease of radiation,
- Adjustment of bandwidth,
- Reduction in height of antenna,
- Avoids mixing of signals,
- Increases the range of communication,
- Multiplexing,
- Efficient transmission, and
- Improved quality of reception.
(i) Easy of Radiation
As the information signals are translated to higher frequencies, it becomes relatively easier to design amplifier circuits as well as antenna systems at these increased (wide) frequencies.
(ii) Adjustment of Bandwidth
Bandwidth of a modulated signal may be made smaller or larger than the original signal.
Signal to Noise Ratio (SNR) at the receiver, which is a function of the signal bandwidth can thus be improved by proper control of bandwidth at the modulating stage.
(iii) Reduction in Height of Antenna
When free space is used as a communication medium, messages are transmitted and received with the help of antennas.
In broadcast systems, the maximum audio frequency transmitted from a radio station is 5 \mathrm{kHz} . The size of antenna needed for an effective radiation would be of the order of the half of wavelength of the signal to be radiated. If the signals are transmitted without modulation, then the antenna height is defined as,
For efficient radiation, at 5 \mathrm{kHz} audio signal requires an antenna of length 30km.The antenna of this height is practically impossible to install.
With the help of modulation this low frequency signal can be translated to the higher frequency range and subsequently radiated efficiently from the reduced size antenna.
Now, consider a modulated signal \mathrm{f}=10 \mathrm{MHz} , the minimum antenna height is given by
\begin{aligned} \text { Minimum antenna height } & =\frac{\lambda}{2}=\frac{c}{2 f} \\ & =\frac{3 \times 10^8}{2 \times 10 \times 10^3} \\ & =15 \text { meter } \end{aligned}The antenna height can be practically achieved.
(iv) Avoids Mixing of Signals
Each modulating signal is modulated with different frequency of carrier signal, and then they will occupy different slots in the frequency domain of the channel bandwidth. Thus modulation avoids mixing of signals.
(v) Increases the Range of Communication
The modulation process increases the frequency of the signal to be transmitted. Hence, increases the range of communication. The attenuation reduces with increase in frequency of the transmitted signals, and thus travels for long distance.
(vi) Multiplexing
The process of multiplex (combine) a number of message signals for simultaneous transmission over a single common channel is known as multiplexing.
If the different message signals transmitted without modulation, over a single channel will interfere with one another. The modulation allows the multiplexing technique such that the interference gets avoided.
Due to multiplexing, the number of channels required will be less. This reduces the cost of installation and maintenance of more channels.
For example, so many TV channels can use the same frequency range, without getting mixed with each other or different frequency signals can be transmitted at the same time. This multiplexing scheme is utilized in long distance telephony, data telemetry etc.
(vii) Efficient Transmission
Here, the frequency of a low-pass signal is translate to a higher band so that the spectrum of the transmitted band pass signal matches the band pass characteristics of the channel for efficient transmission.
(viii) Improved Quality of Reception
To improve noise and interference immunity in transmission over a noisy channel by expanding the bandwidth of the transmitted signal due to modulation process and the effect of noise can be reduced to a great extent. This improves quality of reception of modulated signal.
| Read More Topics |
| Basic types of communication systems |
| Introduction to operational amplifiers |
| Maximum power transfer theorem |
