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Analog signal Transmission
Now a days digital signal transmission is using by many number
of communication systems, it is basic mechanism to study the analog signal
transmission for a good communication student.


Analog signal Transmission is the method of transmitting
analog signal from source to destination in a communication system. The
analog signal is in continues time in nature. Some properties like signal
amplitude, frequency, phase will change continuously in time.
The analog signal represents continuously varying
variables such as temperature, humidity etc.,


Digital signal is one which is having a value at discrete interval
of time. Most computers can understand only digital signals are they are
programmed for on/off understanding so we want to convert analog signal to
digital signal if you are using any computer in between your communication.


The below figure gives the representation of analog and digital
signal.
Analog Signal

The analog signal transmission made possible by the use of ohms law
which gives as V = IR. From this we can collect the varying voltage across
any component which is in the form of analog signal.
While analog signal transmission the most degrading effect is adding
of noise. The noise is one which corrupts the message signal. If we use wires
and cable for analog signal transmission then we can easily decrease the
noise.

The most Used Analog Signal Transmission Mediums

The most used analog signal transmission mediums are:

1. Co-axil cables
2. Twisted pair cables
3. Fiber optic cables
You can send analog signal via water or via ground also.

Advantages of Analog Signal Transmission

analog signal transmission is used in short distance communications
where there is no requirement for time multiplexing and cost is not a
criteria.
2 . For short distance communications we can go for analog signal
transmission in which we can obtain high signal-to-noise ratio.
3 . In analog signal transmission we can use Amplitude Modulation,
Frequency Modulation and Phase modulation techniques.
For long distance communication it is better to go for digital signal
transmission where we can effectively use time division and frequency
division multiplexing.

Introduction to radio signal FM:

Radio signals are popular communication channels because of the large range and variety of techniques.Radio frequency spectrum varies from 30Hz to 300GHz further divided into various sub bands.FM signals come under Very High Frequency band (VHF) ranging from 3 to 30MHz.Frequency modulation is a type of analog modulation in which the frequency of the high frequency carrier is varied with respect to input message signal.Using modulation techniques we can transmit the signal over long distance keeping the information safe and secure.

FM modulation scheme

Generattion and Demodulation of Frequency Modulated (fm) Waves:

Generation: There are basically two techniques of generating frequency modulated waves,viz.,indirect method and direct method.In the former ,a narrow band FM wave is first generated by phase modulating the carrier by integral of message signal.The resulting narrow band phase modulating carrier by the integral of message signal.The resulting narrow band FM wave is then frequency multiplied to give the desired frequency deviation.On the other hand in direct method the carrier frequency is directly varied in accordance with the message signal by means of a voltage controlled oscillator.We can generate the FM signals using digital ICs by providing the proper input signals.

Demodulation: A frequency selective network is used to convert instantaneous frequency variations into amplitude variation.The envelop of the output is the original modulating signal.Frequency demodulation can also be done using a Phase-Locked-Loop(PLL).

Advantages and Applications of Fm Signals:

  • The amplitude of FM wave remains constant. This makes FM more immune to noise due to variations in amplitude of FM waveform which can be eliminated in FM receivers by amplitude limiters.

  • In FM systems the power of transmitted signal depends on the amplitude of the unmodulated carrier signal and hence is constant.

  • FM signals are used to transmit audio signals in analog tv signal transmission.

  • FM signals are used at intermediate frequencies by all analog VCR systems, including VHS, to record black and white luminance also the chrominance portions of the video signal.

  • FM signals are used to synthesize sound at audio frequencies . This technique is popularly known as FM synthesis and applied in  personal computer sound cards.

Introduction to Sound System Amplifier:

An amplifier is an electronic device, which is used to increase the strength of electrical signals in a sound reproduction system.

The amplifier's main function is to receive small sound signal from a sound system and increase it to produce louder sound. Hence the more powerful the Amplifier, the higher the quality of sound produced. A less powerful Amplifier will have a thin and weak sound.

Role of Amplifier in a Sound System

The power is supplied to the speakers by the amplifier.

Among the components of the sound system the amplifier comes just before the speaker. The sound signal travels through the sound system in the following manner:

  • Microphone

  • Sound mixer

  • Compressor

  • Parametric/graphic equalizer

  • Amplifier

  • Speaker(s)

The signal travels to the amplifier only after the sound is mixed and equalized to power the main speakers.

Use of Amplifiers in Sound System

Speakers with low power require a single amplifier, though some sound systems may need to have dual amplifiers or tri-amplifiers. In the case of two amplifiers sound systems, one is for low frequency sounds and the other for high frequency sounds. In the case of three amplifiers systems, one is for low, second for mid range, and the third for high sounds.

The Main System and the Monitor System require Separate amplifiers.

Image on sound amplifier system

Image on sound amplifier system

Four times the power is needed for an amplifier, if the sound is to be twice as loud. 400 watt amplifier = 2 times as loud as 100 watt amplifier.Speakers with amplifiers need to be strategically placed, at a comfortable distance from the audience.

Conclusion to Sound System Involving Amplifier

Low background noise is an important factor for an amplifier.The power consumption of the speakers and amplifier should be same so as not to damage the speakers.Speakers with amplifiers are used in public places like the auditoriums, churches, theaters, movies, stadiums, public rallies and even in private functions. The amplified sounds on such occasions dramatically enhance the effect of the moment.

Introduction:

Communication system is used to conveying a message from one person to other. By means of an information is the attach which holds people jointly. A communication system is known as grouping of processors and hardware used to bring about the transfer of message through communication. This system having some elements for transfer the signal from source to destination.

Communication Systems:

         A communication system is known as grouping of processors and hardware used to bring about the transfer of message through communication. This process of a system allows us to take total unit.

         An energy is need tostart the system. The control mechanism regulates the process. That is, it manipulates the message input into whatever form is necessary. The result of this method is the appearance of message in a form which will permit us for communication to take place.

Elements of Communication Systems

Let us see about elements of communication systems,

Transmitter:

  • It is used for modulation and coding the original signal.
  • In communication system elements, it is used to converting an electrical signal into a form which is comfort for transmission on the physical channel or transmission medium.

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 Channel:

  • In communication system elements, the communications channel is known as a communication medium.
  • It is used to send the signal from the transmitter to the receiver.

The Receiver: 

  • In communication system elements, It is used for demodulation such as decoding the signal from channel.
  • The receiver is used to recover the message signal enclosed in the received signal.

Noise:  

  • In communication system elements, noise is produced at transmitter due to two process

     1. Natural resources 2. Manmade

  • By nature, such as radiation from sun By manmade, noise made from like vehicles.
  • This noise can be reduced by using filter.

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