By:Engr.Yasir Ali

Engr.Ashfaq Ali

Engr. Aamir Khan

(QUEST, Nawabshah)

MODULATIONNEEDS OF MODULATIONDEFINITION OF AM DEFINITION OF FMPM AND FM ARE RELATEDDEFINITION OF PHASE MODULATIONADVANTAGES AND DISADVANTAGES OF PM DEFINATION OF PHASE WIDTH MODULATION ADVANTAGES AND DISADVANTAGES OF PWM

The process of altering the characteristics of the amplitude, frequency, or phase angle of the high-frequency signal in accordance with the instantaneous value of the modulating wave is called modulation.

Need for Modulation • The antenna needed for transmitting signals should have

size at least λ/4.The information signal is of low frequency (and therefore the wavelength is high). If we need to transmit such a signal directly, the size of the antenna will be very large and impossible to build. Hence direct transmission is not practical.

• If we transmit the information signals directly, the signals from different transmitters will get mixed up and the information will be lost.

• When a wave has a large frequency, the energy associated with it will also be large.

Amplitude Modulation (AM):

1Changes the amplitude of the carrier signal according to the amplitude of the message signal.2All information is carried in the amplitude of the carrier.3AM systems usually occupy less bandwidth then FM systems.4AM carrier signal has time-varying envelope.

Frequency Modulation (FM)

In telecommunications and processing of the signal, frequency modulation (FM) conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with the modulation amplitude, which varies the amplitude of the carrier, while its frequency remains constant.

Frequency modulation tends to be used in the transmission of music.

Frequency versus Amplitude Modulation

AM FM

Phase modulation (PM) is a form of modulation that represents information as variations in the instantaneous phase of a carrier wave. Modification in phase according to low frequency will give phase modulation.

PM is not widely used for radio transmissions. This is because it tends to require more complex receiving hardware and there can be ambiguity problems in determining whether, for example, the signal has changed phase by +180° or -180°

What are the advantages and disadvantages of phase modulation?

Advantage – 1. Phase modulation & demodulation is easy compared to

Frequency modulation. 2. Phase modulator is used in determining velocity of moving

target by extracting Doppler information.

3. Doppler information needs stable carrier which is possible in phase modulation but not in frequency modulation.

Disadvantage – 1. Phase ambiguity comes if we exceed its modulation

index pi radian(180 degree).2. we need frequency multiplier to increase phase

modulation index.

PM and FM modulation are related

PM PM is the time integral of FM. The PM carrier phase

deviation is proportional to the amplitude of the modulating signal, constant with respect to the frequency of the modulating signal.

The PM carrier frequency deviation is proportional to the frequency of the modulating signal.

FM FM is the time derivative of

PM. The FM carrier frequency

deviation is proportional to the amplitude of the modulating signal and is constant with respect to the frequency of the modulating signal.

The FM carrier phase deviation is proportional to its frequency deviation and inversely proportional to the

modulating frequency

Pulse width modulation (PWM), also known as pulse duration modulation (PDM), is a digital modulation technique.

PWM is a commonly used technique for controlling power of electrical devices, made practical by modern electronic power switches.

PWM also works well with digital controls, which, because of their on/off nature, can easily set the needed duty cycle

Pulse width modulation:

Advantages & disadvantage of pulse width modulation?

Advantageso Cheap to make. o Little heat whilst workingo Low power consumption. o Can utilize very high frequencies (50-100 KHz is not uncommon.) o Very energy-efficient when used to convert voltages or to dim light bulbs.o High power handling capabilityo Efficiency up to 90%

Disadvantages• Complexity of circuit• Radio Frequency Interference• Voltage spikes• Electromagnetic noise

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• QUESTION?