INTRODUCTION

The process of changing some characteristic (e.g. amplitude, frequency, or phase) of

carrier wave in accordance with the intensity of a signal is known as Modulation. Is the process of varying one or more properties of a high frequency periodic waveform, called the carrier signal, with respect to a modulating signal. This is done in a similar fashion as a musician may modulate a tone (a periodic waveform) from a musical instrument by varying its volume, timing and pitch. The three key parameters of a periodic waveform are its amplitude ("volume"), its phase ("timing") and its frequency ("pitch"), all of which can be modified in accordance with a low frequency signal to obtain the modulated signal. Typically a high-frequency sinusoid waveform is used as carrier signal, but a square wave pulse train may also occur.

Modulation is a process of mixing a signal with a sinusoid to produce a new signal. This new signal, conceivably, will have certain benefits of an un-modulated signal, especially during transmission. If we look at a general function for a sinusoid:

f(t) = Asin(ωt + φ)

we can see that this sinusoid has 3 parameters that can be altered, to affect the shape of the graph. The first term, A, is called the magnitude, or amplitude of the sinusoid. The next term, ω is known as the frequency, and the last term, φ is known as the phase angle. All 3 parameters can be altered to transmit data.

The sinusoidal signal that is used in the modulation is known as the carrier signal, or simply "the carrier". The signal that is being modulated is known as the "data signal". It is important to notice that a simple sinusoidal carrier contains no information of it's own.

In other words we can say that modulation is used because the some data signals are not always suitable for direct transmission, but the modulated signal may be more suitable

Carrier wave-This carrier wave is usually of much higher frequency than the input signal, An electromagnetic wave that can be modulated, as in frequency, amplitude, or phase, to transmit speech, music, images, or other.

Carrier signal Modulating signal Modulated signal

Non-sinusoidal modulation- A sine wave at one frequency can separated from a sine wave at another frequency (or a cosine wave at the same frequency) because the two signals are "orthogonal. There are other sets of signals, such that every signal in the set is orthogonal to every other signal in the set. A simple orthogonal set is time multiplexed division (TDM) -- only one transmitter is active at any one time. Other more complicated sets of orthogonal waveforms -- Walsh codes and various pseudonoise codes such as Gold codes and maximum length sequences -- are also used in some communication systems. The process of combining these waveforms with data signals is sometimes called "modulation", because it is so very similar to the way modulation combines sine waves are with data signals.

BLOACK DIAGRAM OF MODULATED WAVE RADIO BROADCASTING TRANSMISSION : -

Transmitting Aerial Radio Wave

The general principle of radio broadcasting, transmission and reception. As a matter of convenience , the entire arrangement can be divided into three parts viz. Transmission transmitter of radio wave and radio receiver.

1.) Transmitter- A transmitter is an electronic device which, usually with the aid of an antenna propagates an electromagnetic signal such as radio, television, or other telecommunications.

Audio Amplifier

Oscillator Modulator Radio Receiver

MicrophoneReceiving Aerial

2.) Microphone- A microphone (colloquially called a mic or mike; both pronounced is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1876, Emile Berliner invented the first microphone used as a telephone voice transmitter. Microphones are used in many applications such as telephones, tape recorders, karaoke systems, hearing aids, motion picture production, live and recorded audio engineering, FRS radios, megaphones, in radio and television broadcasting and in computers for recording voice, speech recognition, VoIP, and for non-acoustic purposes such as ultrasonic checking or knock sensors.

3.) Audio amplifier-An audio amplifier is an electronic amplifier that amplifies low-power audio signals (signals composed primarily of frequencies between 20 - 20 000 Hz, the human range of hearing) to a level suitable for driving loudspeakers and is the final stage in a typical audio playback chain

4.) Electronic oscillator-An electronic oscillator is an electronic circuit that produces a repetitive electronic signal, often a sine wave or a square wave. They are widely used in innumerable electronic devices. Common examples of signals generated by oscillators include signals broadcast by radio and television transmitters, clock signals that regulate computers and quartz clocks, and the sounds produced by electronic beepers and video games. A low-frequency oscillator (LFO) is an electronic oscillator that generates an AC waveform at a frequency below ≈20 Hz. This term is typically used in the field of audio synthesizers, to distinguish it from an audio frequency oscillator.

5.) MODULATOR- The transmitter stage that supplies the modulating signal to modulated amplifier stage or triggers, A device used to modulate an electromagnetic wave. Addition of information (or the signal) to an electronic or optical signal carrier.

6.) Transmission of radio waves-Radio is the transmission of signals by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space. Information is carried by systematically changing (modulating) some property of the radiated waves, such as amplitude, frequency, phase, or pulse width. When radio waves pass an electrical conductor, the oscillating fields induce an alternating current in the conductor. This can be detected and transformed into sound or other signals that carry information.

7.) Radio receiver- A radio receiver is an electronic circuit that receives its input from an antenna, uses electronic filters to separate a wanted radio signal from all other signals picked up by this antenna, amplifies it to a level suitable for further processing, and finally converts

through demodulation and decoding the signal into a form usable for the consumer, such as sound, pictures, digital data, measurement values, navigational positions, etc.[

NEED FOR MODULATION

Practical Antenna Length (L)

When free space is the communication channel, antennas radiate and receiver the signal . Theory shows that the antennas operate effective only when their dimensions are of the order of the magnitude of wavelength of the signal being transmitted.

The audio frequencies range from 20 Hz to 20 kHz. Suppose a frequency of 20 kHz is to be radiated directly into space. For this,

This is too long antenna to be constructed practically. So, it is impracticable to radiate audio signal directly into space.

Let us now calculate the length of the antenna if a carrier wave of say, 1000kHz is used to carry the signal. An antenna of 300m length can be easily constructed.

Wireless Communication

One desirable feature of radio transmission is that it should be carried without wires (i.e.,) radiated into space. At audio frequencies, radiation is not practicable because the efficiency of radiation is poor. However, efficient radiation of electrical energy is possible at high frequencies (>20kHz). For this reason, modulation is always done in communication systems.

Operating Range

The energy of a wave depends upon its frequency. The greater the frequency of the wave, the greater is the energy possessed by it. As the audio signal frequencies are small, these cannot be transmitted over large distances if radiated directly into space. The only practical solution is to modulate a high frequency carrier wave with audio signal and permit the transmission to occur at this high frequency (carrier frequency).

TYPES OF MODULATIONThere are 3 different types of modulation:

1.) AMPLITUDE MODULATON- When the amplitude of high frequency carrier wave is changed in accordance with the intensity of the signal , it is called amplitude modulation.

Fig. - Modulation depth

Advantages-

The advantage of using a linear RF amplifier is that the smaller early stages can be modulated, which only requires a small audio amplifier to drive the modulator.

Disadvantages-

The great disadvantage of this system is that the amplifier chain is less efficient, because it has to be linear to preserve the modulation. Hence Class C amplifiers cannot be employed. Direct coupling from the audio amplifier is also possible.

2.) FREQUENCY MODULATION-When the frequency of the carrier wave is changed in accordance with the intensity of the signal, it is called frequency modulation. The process of FM can be made more illustrative if we consider numerical values.

Fig.- frequency modulation

Advantages-

1) It give noiseless reception.2) it give high-fidelity reception3) The operating range is quite large.4) The efficiency of transmission is very large.

Application-

Broadcasting, Magnetic Tape Storage, Sound, Radio, Miscellaneous.

3.) PHASE MODULATION- modulation that represents information as variations in the instantaneous phase of a carrier wave. Unlike its more popular counterpart, frequency modulation (FM), PM is not very widely used for radio transmissions. This is because it tends to require more complex receiving hardware and there can be ambiguity problems in determining.

Fig.- Phase modulation

DEMODULATION- Demodulation is the act of extracting the original information-bearing signal from a modulated carrier wave. A demodulator is an electronic circuit (or computer program in a software defined radio) that is used to recover the information content from the modulated carrier wave. These terms are traditionally used in connection with radio receivers, but many other systems use many kinds of demodulators. Another common one is in a modem, which is a contraction of the terms modulator/demodulator.

Fig.- AM DEMODULATION

INDEX

INTRODUCTION NON SINUSOIDAL MODULATION BLOACK DIAGRAM OF MODULATED WAVE RADIO

BROADCASTING TRANSMISSION NEED FOR MODULATION TYPES OF MODULATION

1. AMPLITUDE MODULATON2. FREQUENCY MODULATION3. PHASE MODULATION

REFERENC E

ACKNOWLEDGEMENT

We would like to express our sincere to ……………….(lecturer of EC department) oriental institute of technology & science Jabalpur (MP).

From the very core of our heart .we express our respected and Mr. Manish ranjan for his constant, generous help guidance and timely valuable suggestion during the enter course of work. It has really been a very good experience to work with his and his taught us new mythologies for systematic. His guidance, constant cooperation and friendly behavior inspired us a lot.

AMIT KUMAR SAHU