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Free Online Preparation for Engineering with Minglebox Engineering Prep. Cover basic concepts of under “Section” for Engineering Entrance Exam Preparation with Study material, solved examples and tests prepared by IIT/NIT toppers.

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Communication systems

Electronic communication refers to the faithful transfer of informationor message (available in the form of electrical voltage and current)from one point to another point.

Transmitter, transmission channel and receiver are three basic unitsof a communication system.

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Transducer: Any device that converts one form ofenergy into another can be termed as a transducer. Signal: Information converted in electrical form and suitable for transmission is called a signal. Signals can be either analog or digital.

Noise: Noise refers to the unwanted signals that tend to disturb the transmission and processing of message signals in a communication system.
Transmitter: A transmitter processes the incoming message signal so as to make it suitable for transmis sion through a channel and subsequent reception.
Receiver: A receiver extracts the desired message signals from the received signals at the channel output. Attenuation: The loss of strength of a signal while propagating through a medium is known as attenua tion. Amplification: It is the process of increasing the amplitude (and consequently the strength) of a signal using an electronic circuit called the amplifier.

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Range: It is the largest distance between a source and a destination up to which the signal is received with sufficient strength.
Bandwidth: Bandwidth refers to the frequency range over which an equipment operates or the portion of the spectrum occupied by the signal.
Modulator: At the transmitter, information contained in the low frequency message signal is superimposed on a high frequency wave, which acts as a carrier of the information. This process is known as modulation. As will be explained later, there are several types of modulation, abbreviated as AM, FM and PM. Demodulation: The process of retrieval of information from the carrier wave at the receiver is termed demodulation. This is the reverse process of modulation.

Repeater: A repeater is a combination of a receiver and a transmitter. A repeater, picks up the signal from the transmitter, amplifies and retransmits it to the receiver sometimes with a change in carrier frequency.

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Two important forms of communication system are: Analog and Digital. The information to be transmitted is generally in continuous waveform for the former while for the latter it has only discrete or quantised levels.

Every message signal occupies a range of frequencies. The bandwidth of a message signal refers to the band of frequencies, which are necessary for satisfactory transmission of the infor mation contained in the signal. Similarly, any practical communication system permits transmission of a range of frequencies only, which is referred to as the bandwidth of the system.

Low frequencies cannot be transmitted to long distances. Therefore, they are superimposed on a high frequency carrier signal by a process known as modulation.

In modulation, some characteristic of the carrier signal like amplitude, frequency or phase varies in accordance with the modulating or message signal. Correspondingly , they are called Amplitude Modulated (AM), Frequency Modulated (FM) or Phase Modulated (PM) waves.

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