File Name: comparison between am fm and pm in tabular form .zip
How do the different modulation schemes compare in terms of performance and applications? Thus, we need to have a general idea of which modulation scheme is appropriate for a particular application. Amplitude modulation is straightforward in terms of implementation and analysis.
- Difference between AM and FM
- Difference between AM and FM
- Comparing and Contrasting Amplitude, Frequency, and Phase Modulation
AM and FM are two methods of transmitting information through radio signals. In both the methods, the carrier wave is modified in order to transmit data, information or sound. Let us see how AM differs from FM. AM is a method of broadcasting radio signals.
Difference between AM and FM
How do the different modulation schemes compare in terms of performance and applications? Thus, we need to have a general idea of which modulation scheme is appropriate for a particular application. Amplitude modulation is straightforward in terms of implementation and analysis. Also, AM waveforms are fairly easy to demodulate. Overall, then, AM can be viewed as a simple, low-cost modulation scheme. As usual, though, simplicity and low cost are accompanied by performance compromises—we never expect the easier, cheaper solution to be the best one.
However, the applications of analog amplitude modulation are currently quite limited, because AM has two significant disadvantages. Noise is a perpetual difficulty in wireless communication systems. In a certain sense, the quality of an RF design can be summarized by the signal-to-noise ratio of the demodulated signal: less noise in the received signal means higher quality output for analog systems or fewer bit errors for digital systems.
Noise is always present, and we always have to recognize it as a fundamental threat to the overall performance of the system. Noise—random electrical noise, interference, electrical and mechanical transients—operates on the magnitude of a signal.
In other words, noise can create amplitude modulation. This is a problem, since the random amplitude modulation resulting from noise cannot be distinguished from the intentional amplitude modulation performed by the transmitter.
Noise is a problem for any RF signal, but AM systems are particularly susceptible. One of the primary challenges in the design of RF power amplifiers is linearity.
More specifically, it is difficult to achieve both high efficiency and high linearity. A linear amplifier applies a certain fixed gain to the input signal; in graphical terms, the transfer function of a linear amplifier is simply a straight line, with the slope corresponding to the gain. Real-life amplifiers always have some degree of nonlinearity, meaning that the gain applied to the input signal is affected by the characteristics of the input signal.
The result of nonlinear amplification is distortion, i. We can also say that nonlinear amplification is a form of amplitude modulation. If the gain of an amplifier varies according to the frequency of the input signal, or according to external factors such as temperature or power-supply conditions, the transmitted signal is experiencing unintended and undesirable amplitude modulation. This is a problem in AM systems because the spurious amplitude modulation interferes with the intentional amplitude modulation.
Any modulation scheme that incorporates amplitude variations is more susceptible to the effects of nonlinearity. This includes both ordinary analog amplitude modulation and the widely used digital schemes known collectively as quadrature amplitude modulation QAM. Frequency and phase modulation encode information in the temporal characteristics of the transmitted signal, and consequently they are robust against amplitude noise and amplifier nonlinearity.
The frequency of a signal cannot be changed by noise or distortion. Additional frequency content may be added, but the original frequency will still be present. Noise does, of course, have negative effects on FM and PM systems, but the noise is not directly corrupting the signal characteristics that were used to encode the baseband data. As mentioned above, power-amplifier design involves a trade-off between efficiency and linearity.
Angle modulation is compatible with low-linearity amplifiers, and these low-linearity amplifiers are more efficient in terms of power consumption. Thus, angle modulation is a good choice for low-power RF systems.
The frequency-domain effects of amplitude modulation are more straightforward than those of frequency and phase modulation. However, the difficulty of predicting the spectral characteristics of FM and PM is more relevant to the theoretical portion of the design. If we focus on practical considerations, angle modulation could be considered advantageous because it can translate a given baseband bandwidth to a somewhat smaller compared to AM transmission bandwidth.
Frequency modulation and phase modulation are closely related; nevertheless, there are situations in which one is a better choice than the other. The differences between the two are more pronounced with digital modulation. As we saw in the page on phase modulation , when the baseband signal is a sinusoid, a PM waveform is simply a shifted version of a corresponding FM waveform. PM pros and cons related to spectral characteristics or noise susceptibility.
However, analog FM is much more common than analog PM, and the reason is that FM modulation and demodulation circuitry is more straightforward. For example, frequency modulation can be accomplished with something as simple as an oscillator built around an inductor and a voltage-controlled capacitor i.
The differences between PM and FM become quite significant when we enter the realm of digital modulation. The first consideration is bit error rate. Obviously the bit error rate of any system will depend on various factors, but if we mathematically compare a binary PSK system to an equivalent binary FSK system, we find that binary FSK needs significantly more transmit energy to achieve the same bit error rate.
This is an advantage of digital phase modulation. Don't have an AAC account? Create one now. Forgot your password? Click here. Latest Projects Education. Amplitude Modulation Amplitude modulation is straightforward in terms of implementation and analysis. In addition to AM radio broadcasting, analog amplitude modulation is used in civil aviation. Amplitude Noise Noise is a perpetual difficulty in wireless communication systems.
Amplifier Linearity One of the primary challenges in the design of RF power amplifiers is linearity. A straight line represents the response of a perfectly linear amplifier: the output voltage is always the input voltage multiplied by a fixed gain. Angle Modulation Frequency and phase modulation encode information in the temporal characteristics of the transmitted signal, and consequently they are robust against amplitude noise and amplifier nonlinearity.
Bandwidth The frequency-domain effects of amplitude modulation are more straightforward than those of frequency and phase modulation. Frequency vs. Phase Frequency modulation and phase modulation are closely related; nevertheless, there are situations in which one is a better choice than the other. Analog Frequency and Phase Modulation As we saw in the page on phase modulation , when the baseband signal is a sinusoid, a PM waveform is simply a shifted version of a corresponding FM waveform.
But ordinary digital PM also has two significant disadvantages. FSK, in contrast, does not require coherent detection. Ordinary PSK schemes, especially QPSK, involve abrupt phase changes that result in high-slope signal variations, and high-slope sections of the waveform decrease in amplitude when the signal is processed by a low-pass filter.
These amplitude variations combined with nonlinear amplification lead to a problem called spectral regrowth.
To mitigate spectral regrowth we can either use a more linear and thus less efficient power amplifier or implement a specialized version of PSK. Here you can see amplitude variations caused by low-pass filtering a PSK signal. Summary Amplitude modulation is simple, but it is susceptible to noise and requires a high-linearity power amplifier. Frequency modulation is less susceptible to amplitude noise and can be used with higher-efficiency, lower-linearity amplifiers.
Digital phase modulation offers better theoretical performance in terms of bit error rate than digital frequency modulation, but digital FM is advantageous in low-power systems because it does not require a high-linearity amplifier.
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Difference between AM and FM
Prerequisite — Modulation. Frequency Modulation : Frequency Modulation is a modulation in which the frequency of the carrier wave changes according to the instantaneous amplitude of the modulating signal keeping phase and amplitude constant. The frequency of the carrier wave is modified in order to send the data or information. It cannot transmit over long distances, have a smaller range. Its modulation index is always greater than one. In Frequency Modulation amplitude and phase remain the same.
Both transmit the information in the form of electromagnetic waves. AM works by modulating varying the amplitude of the signal or carrier transmitted according to the information being sent, while the frequency remains constant. This differs from FM technology in which information sound is encoded by varying the frequency of the wave and the amplitude is kept constant. AM method of audio transmission was first successfully carried out in the mid s to produce quality radio over telephone lines and the original method used for audio radio transmissions. FM radio was developed in the United states mainly by Edwin Armstrong in the s. AM radio ranges from to kilohertz, whereas FM radio ranges in a higher spectrum from 88 to megahertz. The advantages of AM radio are that it is relatively easy to detect with simple equipment, even if the signal is not very strong.
AM, PM and FM modulation Amplitude modulation, AM, is one of the most straightforward ways of A radio frequency signal consists of an oscillating carrier in the form of a sine wave is be said to have a phase difference between them.
Comparing and Contrasting Amplitude, Frequency, and Phase Modulation
The term carrier is applied to the voltage whose characteristic is varied and the term modulating voltage signal is used for the voltage in accordance with which the variation is made. The modulation is the process of up shifting the message frequency to a range more useful for transmission. The carrier signal is a sine wave at the carrier frequency. Below equation shows that the sine wave has three characteristics that can be altered. So three forms of modulations are possible.
A sudden, large reduction in the amplitude of the input AM wave means that capacitor pressing the carrier and leaving only the sum and difference frequencies at the output.
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