Train

1 January 2017

In analog technology, compare and contrast the advantages and disadvantages of amplitude modulation, frequency modulation, phase modulation, and Quadrature Amplitude Modulation There are several advantages of amplitude modulation, and some of these reasons have meant that it is still in widespread use today. It is simple to implement, it can be demodulated using a circuit consisting of very few components, and AM receivers are very cheap as no specialized components are needed (“Electronics and Radio Today”, n. d. ). Disadvantages: Amplitude modulation is a very basic form of modulation, and although its simplicity is one of its major advantages, other more sophisticated systems provide a number of advantages.

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Accordingly it is worth looking at some of the disadvantages of amplitude modulation. It is not efficient in terms of its power usage, it is not efficient in terms of its use of bandwidth, requiring a bandwidth equal to twice that of the highest audio frequency, and it is prone to high levels of noise because most noise is amplitude based and obviously AM detectors are sensitive to it (“Electronics and Radio Today”, n. d. ). Frequency Modulation Frequency nodulation (FM) sends information over a carrier wave by varying its instantaneous frequency.

In analog applications, the difference between the instantaneous and the base frequency of the carrier is directly proportional to the instantaneous value of the input-signal amplitude. FM is commonly used for broadcasting music and speech, two way radio systems, magnetic tape recording systems, and some video transmission systems. FM signals can be generated using either direct or indirect frequency modulation. Direct FM modulation can be achieved by directly feeding the message into the input of a voltage controlled oscillator (VCO).

For indirect FM modulation, the message signal is integrated to generate a phase-modulated signal. This is used to modulate a crystal-controlled oscillator, and the result is passed through a frequency multiplier to give an FM signal (“Electronics and Radio Today”, n. d. 1). FM is used for a number of reasons and there are several advantages of frequency modulation. In view of this it is widely used in a number of areas to which it is ideally suited. Some of the advantages of frequency modulation are noted below: Resilience to noise: One particular advantage of frequency modulation is its resilience to signal level variations.

The modulation is carried only as variations in frequency. This means that any signal level variations will not affect the audio output, provided that the signal does not fall to a level where the receiver cannot cope. As a result this makes FM ideal for mobile radio communication applications including more general two-way radio communication or portable applications where signal levels are likely to vary considerably. The other advantage of FM is its resilience to noise and interference. It is for this reason that FM is used for high quality broadcast transmissions.

Easy to apply modulation at a low power stage of the transmitter: Another advantage of frequency modulation is associated with the transmitters. It is possible to apply the modulation to a low power stage of the transmitter, and it is not necessary to use a linear form of amplification to increase the power level of the signal to its final value. It is possible to use efficient RF amplifiers with frequency modulated signals: It is possible to use non-linear RF amplifiers to amplify FM signals in a transmitter and these are more efficient than the linear ones required for signals with any amplitude variations (e. . AM).

This means that for a given power output, less battery power is required and this makes the use of FM more viable for portable two-way radio applications (“Electronics and Radio Today”, n. d. 1). Phase Modulation Phase modulation (PM) is a form of 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 (“Radio-Electronics. com”, n. d. ). Advantage: The main advantage of PM like FM is increased immunity to noise. Disadvantage: The main disadvantage to PM is that it requires more complex receiving hardware (M. S. Richer, 2006). Quadrature Amplitude Modulation Quadrature amplitude modulation (QAM) is both an analog and a digital modulation scheme. It conveys two analog message signals, or two digital bit streams, by changing (modulating) the amplitudes of two carrier waves.

The two carrier waves, usually sinusoids, are out of phase with each other by 90° and are thus called quadrature carriers or quadrature components. Analog QAM is used in National Television System Committee (NTSC) and Phase Alternating Line (PAL) television systems (“Radio-Electronics. com”, n. d. ). Advantages: With QAM sharp cutoff band pass filters are not required. This makes it an attractive alternative to single sideband-suppressed carrier (SSB-SC). Disadvantages: Compared to SSB, QAM is more exacting in terms of the carrier

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