In this experiment, you will examine the characteristics of amplitude modulation am. Connect channel 1 probe of the oscilloscope to the output of the modulator at pin 7. Digitalsoftware iq modulation digital iq modulation avoids a few of the problems associated with analog iq modulators. It is often called as am and is commonly used in transmitting a piece of information through a radio carrier wave.
Vector modulation and frequency conversion fundamentals. Overmodulation overmodulation is a condition that occurs when an excessive intelligence signal overdrives an am modulator making %m 100% because e i e c modulated carrier amplitude reach value greater than double of unmodulated value it produces a distortion known as sideband splatter, which results on transmission at frequencies outside. Frequency modulation and phase modulation are the two complementary principal methods of angle modulation. The modulating signal contains the intended message or information sometimes consisting of audio data, as in am radio. In this method of modulation the amplitude of the carrier wave is maintained. That could be the amplitude, phase, or frequency, which result in amplitude modulation am, phase modulation pm, or frequency modulation fm. Use the spectrum analyzer to compare this modulator to the one in part 2. Amplitude modulation am frequency modulation fm phase modulation pm click on the links given above to know more. Essentially an amplitude modulated wave consists of a radio frequency carrier a sine wave at one frequency, typically in the radio frequency portion of the spectrum. Amplitude modulation am is a modulation technique where the. A carrier wave is purely made up of constant frequency, slightly similar to a sine wave.
The third term must, therefore, be a wave with frequency equal to the carrier frequency minus the modulator frequency. Once a signal has been modulated, information is retrieved through a demodulation process. When the rf carrier wave is amplitude modulated, sidebands or sideband fre. Amplitude and frequency modulation hp memory project. First, at low frequencies the noise of the lmr spectrometer increases due to vibrations of the spectrometer. Amplitude modulation is a process by which the wave signal is transmitted by modulating the amplitude of the signal. Therefore, both fm and pm are often referred to as angle modulation. Failure to accurately recover this intelligence will result in distortion and degradation of the demodulated signal and intelligence will be lost.
Transmit two pam signals using carriers of the same frequency but in phase and quadrature demodulation. Figure 1b shows the carrier and sideband components of the amplitude modulated wave of figure 1a as they would appear in the. The concepts of amplitude modulation, modulation and demodulation, along with their. In modulation, one characteristic of a signal generally a sinusoidal wave known as the carrier is changed based on the information signal that we wish to transmit modulating signal. It is strongly suggested that you examine your text book for other methods. Amplitude modulation am and frequency modulation fm. Phase modulation pm is a different form of frequency modulation and the carrier is similar in appearance to a frequencymodulated carrier. Some parameter of the carrier amplitude, frequency, phase is varied in accordance with the baseband signal xt t. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation. Explain briefly in your report how amplitude modulation is accomplished by this circuit.
The left and right channels each limited to 15khz are multiplexed into a single baseband signal using amplitude modulation using frequency modulation to shift the baseband. Second, the modulation amplitude decreases inversely with the square root of f at a fixed power of the generator for. In other words, amplitude modulation allows the original carrier waveform through the vca, and also creates two new signals called the sum and the difference signals. Practical circuitry is more likely to use a modulator, rather than the more idealised multiplier. For example, the signal in a cell phone is a voice signal with a bandwidth of about 4 khz. Remember, for analysis purposes keep the modulation index and frequency the same as part 2, step 3. As a 250 mvpp amplitude of audio signal is applied to the carrier signal, the percentage modulation is set to 50% by adjusting the vr1. The carrier frequency, fc, should be larger than the highest spectral component. No inband carrier feedthrough no inband images generally less signal power due to the insertion loss of the mixer frequency response is still not flat 39. This principle is at the heart of amplitude modulation.
In this video, i have explained amplitude modulation by following outlines. The typical frequency of the transmitted and received signal is. The original method of electronically encoding sound information on radio waves is called amplitude modulation, or am. Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example. Quadrature amplitude modulation qam pam signals occupy. Am modulators base, collector, grid and plate modulators. Turn the power supply on and capture the am signal and its spectrum by executing timefreq. Chichinin, in encyclopedia of spectroscopy and spectrometry, 1999. Amplitude modulation definition, types, solved examples. Notice that the sine wave will move up and down as the dc is varied, its mean value equalling the dc value. Am is a relatively simple way to add audio information to a carrier wave so that sounds can be transmitted. Modulation frequency an overview sciencedirect topics. When n0 no modulation, when n1 100% modulation, when n1. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information.
The frequency of a radiofrequency channel can be explained best as the frequency of a carrier wave. So can have amplitude modulation am frequency modulation fm phase modulation pm frequency and phase combined are known as angle modulation 8. Using amplitude modulation to shift the baseband signal fm radio 88mhz108 mhz. Qam transmitter implementation qam is widely used method for transmitting digital. The pulse may take any real voltage value that is proportional to the value of the original waveform. Types of modulation sine wave carrier described by 3 parameters. It does not carry much information that we can relate to data or speech. The modulation depth am or frequency deviation fm is controlled by the signal level on the rearpanel modulation in connector. In order that a radio signal can carry audio or other information for broadcasting or for two way radio communication, it must be modulated or changed in some. Amplitude modulation is mostly used in the form of electronic communication. Farshad lahouti january 20, 2003 winter 2003 uw, ece 318 lecture notes 2 information source signal modulator propagation channel signal demodulator information destination analog communication system analog signals may be transmitted directly via carrier modulat ion over. Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation.
Serial to parallel map to constellation point impulse modulator impulse modulator pulse shaping filter pulse. Modulationtypesamplitude,frequency,phase modulation. For a perfect modulation, the value of modulation index should be 1, which implies the percentage of modulation should be 100%. In this modulator the amplitude of a carrier is varied in accordance with instantaneous value of message signal. The distortion may be in amplitude, frequency, or phase, depending on. Am modulator is one which is used for superimposing a low frequency signal on a high frequency carrier signal.
The external modulation input has 3 db bandwidth of 100 khz. The original waveform amplitude is quantized with a resulting loss of information. These videos explain you what is modulation, different kinds of modulations like amplitude modulation am and frequency modulation fm,qpsk,qam,phase modulation etc. Angle modulation changes the phase of a signal as well as its amplitude, where amplitude modulation leaves the phase unchanged. The components of each carrier are called inphase and quadrature. The modulation frequency f is determined as a compromise between two factors. Each radio station is assigned 200 khz, to transmit a stereo audio.
The typical frequency of the transmitted and received signal is several hundreds. Both modulated carriers are summed to result in a signal with amplitude and phase modulation. Phase modulation is another type of angle modulation very similar to frequency modulation. It was developed in the first few decades of the twentieth century. Amplitude modulation and frequency modulation youtube. The paper presents an introduction to a novel application of the. Amplitude modulation, frequency changers, power conversion.
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