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Communication and Modulation

January 28th, 2011 admin


Telecommunication is the transmission of signals over a distance for the purpose of communication. In modern times, this process typically involves the sending of electromagnetic waves by electronic transmitters, but in earlier years it may have involved the use of smoke signals, drums or semaphore.

In a broadcast system, a central high-powered broadcast tower transmits a high-frequency electromagnetic wave to numerous low-powered receivers. The high-frequency wave sent by the tower is modulated with a signal containing visual or audio information. The antenna of the receiver is then tuned so as to pick up the high-frequency wave and a demodulator is used to retrieve the signal containing the visual or audio information. The information signal can be either analog (signal is varied continuously with respect to the information) or digital (information is encoded as a set of discrete signal values).

Basic elements: Each telecommunication system consists of three basic elements:

a transmitter that takes information and converts it to a transmit signal

a transmission medium over which the signal is transmitted

a receiver receives the transmit signal and converts it back into usable information

In this project only one way communication is taken into account. So this communication system falls under the category of Simplex.

Communication is simply the process of conveying message at a distance or communication is the basic process of exchanging information.

Information source produces required message which has to be transmitted.

Input transducer is a device which converts one form of energy to another form of energy. It converts information source output to a electrical signal.

What is Modulation:-

Modulation may be defined as a process by which some characteristics of a signal known as carrier is varied according to the instantaneous value of another signal known as modulating or base band signal. The signals containing intelligence or information to be transmitted are called the modulating signals. The carrier frequency is much greater than the base band signal frequency.

In the context of using antennas to radiate the transmitter output, modulation is used since we know that for efficient radiation

antenna height (l) = (wave length) / 4= velocity of light/(4*frequency).

That’s why modulation is done when audio frequency is transmitted using a radio frequency carrier in the MHz range, so antenna height is reduced.

Transmitter is used to modulate a carrier signal to produce a transmit signal.

Communication channel is the medium (e.g. optical fiber, free space etc.) through which the transmit signal travels from transmitter to receiver. Noise is unwanted signals which tend to interfere with the required signal.

Receiver reproduces the message signal in electrical form from noisy & distorted received signal.

Destination is the final stage which is used to convert an electrical message signal into its original form.

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