COMMUNICATION SYSTEMS
The process of sending an information from one point to another is called communication.
The system of devices which are used for this process are collectively called communication systems.
Communication Systems:
- Analog Communication System
- Digital Communication System
1. Analog Communication Systems:
The communication system which makes use of analog signal is called analog communication system.
Some terms related to analog communication systems:
- Telegraphy: It is used for sending electric signal in the form of code
- Telephony: It can send voice signals from one place to another by means of wire
2. Digital Communication Systems:
The communication system which makes use of digital signal is called digital communication system.
Some terms related to digital communication systems:
- Fax: It is used for facsimile transmission and receiving texts and paragraphs
- Electronic Mail (E-mail): The messages sent via a computer network are called E-mail.
- Global Positioning System (GPS): It is a navigation system based on the network of earth-orbiting satellites
Elements of Communication Systems:
There are three parts of communication systems:
- Transmitter: It transmits information signal
- Communication channel: The medium through which information propagates from transmitter to receiver is called communication channel
- Receiver: It receives and decodes the signal
Modulation:
The process of superimposing the audio signal over a high frequency carrier wave is called modulation
Need of Modulation:
- Energy carried by low frequency audio wave is very small
- For efficient radiation and reception of signal
- The frequency range of audio signal is so small
Types of modulation:
- Amplitude modulation (AM): In this type of modulation, the amplitude of high frequency carrier wave is varied with instantaneous amplitude of modulating signal
- Frequency modulation (FM): In this type of modulation, the frequency of high frequency carrier wave is varied with instantaneous frequency of modulating signal
- Pulse modulation: In this type of modulation, the continuous waveform are sampled at regular intervals; Information is transmitted only at sampling time
Demodulation:
The process of separating of audio signal from modulated signal is called demodulation
Antenna: An antenna converts electrical energy in electromagnetic wave at transmitting end and picks up transmitted signal at receiving end to convert electromagnetic wave into electrical signal
Modem: The device which can both, modulate and demodulate the signal is called modem
Radio Wave: The radio wave is an electromagnetic wave of frequency range from 3 kHz to 300 GHz
Propagation of Radio Wave:
- Ground wave propagation: It is suitable for low and medium frequency up to 2 MHz. It is used for local broadcasting
- Sky-Wave Propagation: It is suitable for radio wave of frequency from 2 MHz to 30 MHz. It is used for long distance radio communication.
- Line of Sight Propagation:
