AM and FM Transmitters - Electrical Engineering - Lecture Slides, Slides for Electrical Engineering. Alagappa University
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dheemant31 December 2013

AM and FM Transmitters - Electrical Engineering - Lecture Slides, Slides for Electrical Engineering. Alagappa University

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This lecture series is from Electrical Engineering courses. A collection of lectures on all the important topics in EE. These slides covers points such as: Am and Fm Transistors, Block Diagram, Transmitter, Basic Blocks ...
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Microsoft PowerPoint - AM and FM Transmitters - Electrical Engineering - Lecture Slides [Compatibility Mode]

LECTURE ON AM/FM TRANSMITTER

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Block diagram of communication system

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Information or Message

Transducer Transmitter Communication Channel or

Medium Information

in Electrical form

• It takes the information to be communicated in electrical form and convert it into an electronic signal compatible with the communication medium .

TRANSMITTER

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TRANSMITTER

 In this block diagram of communication system, the upper section is called the transmitting section.

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TRANSMITTER

 The main parts of transmitter are explained as follows :

 Microphone : It converts sounds into electrical signals in wires. It is the opposite of a loudspeaker.

 Modulator : The audio signal is modulated into the radio frequency carrier in this modulator stage.

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TRANSMITTER

 Frequency generator : The frequency generation stage will decide the frequency on which the transmitter will operate.

 RF power amplifier : The power amplification of the radio signal is carried out in the final stage. It makes the signal stronger so that it can be transmitted through the channel over long distances.

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TRANSMITTER

 An antenna is a transducer which converts electrical signals into electromagnetic waves.

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BASIC BLOCKS OF TRANSMITTER

 Modulator

 RF oscillator

 Power amplifier

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BASIC FUNCTIONS OF TRANSMITTER

 Modulation  Carrier generation  Amplification (Power)

 It is an electronic unit which accepts the information signal to be transmitted and converts it into an RF signal capable of being transmitted over long distances .

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BASIC FUNCTIONS OF TRANSMITTER

Every transmitter has three basic functions as follows:

 The transmitter must generate a signal of correct frequency at a desired point in the spectrum.

 Secondly it must provide some form of modulation to modulate the carrier.

 Third it must provide sufficient power amplification in order to carry the modulated signal to a long distance.

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CLASSIFICATION OF RADIO TRANSMITTERS

1. According to the type of modulation used.

2. According to service involved.

3. According to the frequency range involved.

4. According to the power used.

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CLASSIFICATION BASED ON TRANSMITTED FREQUENCY

 Low frequency (LF) transmitters (30 KHZ- 300KHZ)

 Medium frequency (MF) transmitters ( 300 KHZ- 3 MHZ)

 High frequency (HF) transmitters (3 MHZ- 30MHZ)

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CLASSIFICATION BASED ON TRANSMITTED FREQUENCY

 Very high frequency (VHF) transmitters (30MHZ-300 MHZ)

 Ultra high frequency (UHF) transmitters (300 MHZ- 3GHZ)

 Microwave transmitters (>3GHZ)

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CLASSIFICATION BASED ON TYPE OF SERVICE INVOLVED

 Radio broadcast transmitters.

 Radio telephony transmitters.

 Radio telegraph transmitters.

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CLASSIFICATION BASED ON TYPE OF SERVICE INVOLVED

 Television transmitters.

 Radar transmitters.

 Navigational transmitters.

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CLASSIFICATION BASED ON TYPES OF MODULATION

 CW Transmitters

 AM Transmitters

 FM Transmitters

 SSB Transmitters

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CONTINIOUS WAVE (CW) TRANSMITTERS

 The CW Transmitter is the simplest type of transmitter.

 It is a simple crystal oscillator circuit.

 This oscillator generates a carrier signal of the desired frequency.

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CONTINIOUS WAVE (CW) TRANSMITTERS

 Information to be transmitted is expressed in a special form of code using dots and dashes to represent letters of the alphabet and numbers.

 The information transmitted in this way is called as continuous wave (CW) transmission.

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CONTINIOUS WAVE (CW) TRANSMITTERS

 The key is a simple hand operated switch connected in emitter of the transistor.

 By closing the key we can turn on the crystal oscillator on and by opening the key the oscillator is turned off.

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CONTINIOUS WAVE (CW) TRANSMITTERS

 When the key is closed, the oscillator produces a sinusoidal signal at a frequency equal to the crystal frequency, whereas with the key open, the output of oscillator is zero.

 The key is opened and closed in order to produce zero output and dots or dashes.

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CONTINIOUS WAVE (CW) TRANSMITTERS

 Dots correspond to the short duration output whereas a dash corresponds to a long duration output.

 The required messages can be transmitted using different combinations of dots and dashes for different alphabets and letters.

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ADVANTAGES OF CW TRANSMITTER

 Simple to construct

 Compact and portable

 Can be operated on batteries

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DISADVANTAGES

 A skilled operator is required to convert the message to be sent into a coded form of dots and dashes.

 Long distance communication is not possible.

 Voice or picture can not be sent.

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AM TRANSMITTER

 Amplitude modulation technique is used in AM transmitters, here the amplitude of carrier is varied in proportion with the amplitude of the modulating signal, keeping its frequency and phase constant.

 Used in radio & TV broadcasting.

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AM TRANSMITTER

 In AM Transmitter, AM signal is transmitted by a transmitter. The information is contained in its amplitude variation.

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