Table of Contents
ANALOG AND DIGITAL CIRCUITS
Analog vs. Digital
There are two types of electronic circuits:
(i) Analog circuits and
(ii) Digital circuits.
Analog Electronic Circuit:
Analog means continuous. Therefore, in an analog Circuit the voltage (or current) varies continuously with time. Such a voltage (or current) is called an analog signal. The sinusoidal variation +5V of voltage signal between-5 V and + 5 V is an example of analog signal.
Digital Electronic Circuit:
Digital signal means the signal divided into digits. For convenience, the signal is divided into several parts and the parts -5V are named in the form of digits 1, 2, 3,.
Nowadays, digital circuits are being popular because of their use in computers, fax machines, electronic counting systems, telephone switching and control of traffic signals.
The simplest digital signal contains only two levels: zero or a +5V constant voltage. These are symbolised in the form of digits 0 and 1. A signal having only two levels of voltage (or current) is called a digital signal.(b) shows a typical digital voltage signal, having voltage at any time either 0 or +5 V. In digital circuits the binary number system is used, according to which the two levels of the signal are denoted by two digits: 0 and 1 only. The logic gates are examples of (b) the digital circuits.
ELEMENTS OF A COMMUNICATION SYSTEM
Communication means sending a message (information) from one place and receiving it at the other place, through some means (e.g, by cables, by electromagnetic waves).
A communication system basically contains three elements.
(i) Transmitter:
The transmitter converts the message (or information) signal into a suitable signal which may be passed on to a suitable medium called the transmission channel. The signal processing for transmission usually involves modulation and coding.
(ii) Transmission Channel:
It is the medium that carries the message in the form of a suitable signal from one place to another. It may be a pair of wires, a coaxial cable, a radio wave or a laser beam. Every channel involves loss of energy during transmission. That is why, the signal power goes on decreasing with increasing
(iii) Receiver:
Receiver converts the suitable signal prepared by the transmitter into actual message (or information). Receiver distance. operations include amplification of signal to compensate for the transmission loss, demodulation and decoding to reverse the signal processing performed by the transmitter. The three components of a transmission system are sketched below.
There are three possibilities:
(i) the speaker and listener are close
(ii) the speaker and listener are at a distance of few kilometres
(iii) the speaker and listener are at quite a large distance.
(i) When speaker and listener are close:
When two persons talk to each other, the speaker is the transmitte Conveying the information, the intervening medium air is the transmission channel and the listener is the receiver. This is the simplest form of communication system. In this system, the information is carried in air through sound waves. These sound waves produced by the speaker are the signals. If the distance between the speaker and the listener is small, the signals can be received by the listener through air directly.
(ii) When speaker and listener are at a distance of a few kilometres:
If the distance between the speaker and listener is large and covers several kilometres, then the sound waves produced by speaker are attenuated and it is ever reaches the listener (or receiver). In such cases, the sound waves are converted into electrical signals (by a microphone). These signals can travel through wires over long distances and reach the receiver end where they are converted back into sound waves using a loudspeaker. It must be kept in mind that a microphone converts sound signals into electrical signals, while a loudspeaker converts electrical signals back into sound signals.
(iii) If the distance between the speaker and listener is quite large:
If the distance between the speaker and listener is quite large, then wires as a transmission channel cannot serve the purpose. In such cases, the sound signals are converted into electrical signals, their power is increased by power amplifiers and amplified signals are allowed to radiate through space with the aid of an antenna. This would constitute a usual transmitter.
At the receiving end, the antenna picks up the electrical signal, which is fed to the amplifier and finally to the speaker which converts electrical signals into sound signals (or output message). This would be a constant usual receiver.
Basic Modes of Communication
These are two basic modes of communication
(i) Point to Point communication
(ii) Broadcast communication
In point to point communication mode, the communication takes place over a link between a signs Other transmitter and receiver. The example of such a mode of transmission is Telephone.
In broadcast communication, there are a large number of receivers corresponding to a single transmite the examples of broadcast mode of communication are Radio and Television.
DEFINITION OF TERMS USED IN ELECTRONIC COMMUNICATION SYSTEM
(I) signal:
the information converted into electrical or optical form, whichever is suitable for transit
called a signal. The signal may be Analog or Digital.
(ii) Transducer:
A transducer is a device which converts one form of energy into.another of communication system, it is usually desired to convert a message (or information) signs of out of bressuire, displacement, temperature, etc.) into corresponding variations in the electrical signal at transmitter and then electrical signal into the information signal at the output of receiver
(iii) Noise:
The unwanted signal that tends to disturb the transmission and reception or the communication system, is called noise. In other words, any disturbance in the signal is called noise.
(iv) Attenuation:
The loss of strength of a signal while propagating through a medium is called attention.
(V) Amplification:
The process of increasing the strength of a signal by using an electronic circuit 5 the anpuucaton. Amplification is necessary to compensate for attenuation of signal in a Communication channel.
(vi) Range:
It is the largest distance between transmitting and receiving ends upto which the signal gas has sufficient strength.
(vii) Bandwidth:
Bandwidth is the frequency range of waves occupied by the signal. The band width is different for audio and video signals.
(viii) Repeater:
A repeater is a combination of a receiver and a transmitter. Repeaters are used to increase the range or communication of signals. A repeater picks up the signal from the transmitter, amplifies and transmits it to the receiver, sometimes with a change in carrier frequency.