...properties of various modulation techniques. The modulation techniques described here have a long history in radio applications. The information to be transmitted is normally an analog so called baseband signal. By that we understand a signal with the main part of its spectrum around zero. Especially, that means that the main part of the spectrum is below some frequency W , called the bandwidth of the signal. We also consider methods to demodulate the modulated signals, i.e. to regain the original signal from the modulated one. Noise added by the channel will necessarily affect the demodulated signal. We separate the analysis of those demodulation methods into one part where we assume an ideal channel that does not add any noise, and another part where we assume that the channel adds white Gaussian noise. 5.1 Amplitude Modulation Amplitude modulation, normally abbreviated AM, was the first modulation technique. The first radio broadcasts were done using this technique. The reason for that is that AM signals can be detected very easily. Essentially, all you need is a nonlinearity. Actually, almost any nonlinearity will suffice to detect AM signals. There have even been reports of people hearing some nearby radio station from their stainless steel kitchen sink. And some 67 68 Chapter 5. Traditional Analog Modulation Techniques (including the author) have experienced that with a guitar amplifier. The crystal receiver is a demodulator for AM that can be manufactured at...
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...V Time V Fig.1.4 Amplitude-modulatedwave of modulation depth greater than 100% v The maximum value of the modulation factor is limited to 1 since this gives a minimum value to the envelope of Ve(1-I) or zero. If a greater value of modulation factor is used, the envelope will no longer be sinusoidal (Fig. 1.4) and the waveform will contain a number of extra, unwanted frequency components. Power Contained in an Amplitude-modulated Wave The expression for the instantaneous voltage of an amplitudemodulated wave, equation (1.2), can be rewritten in terms of the modulation factor m: (1.7) (1.8) The power developed by an amplitude-modulated wave is the sum of the powers developed by the carrier frequency, upper sidefrequency and lower sidefrequency components. The carrier power is (V)2I R .J~ 2.J2 R V2 or 2~ watts and the power developed by each of the two sidefrequencies is mVe)2 1 m2V~ - or --watts ( -8R so that the TOTAL POWER is AMPLITUDE MODULATION 7 As previously mentioned, the maximum modulation factor used in practice is m = 1, and for this condition PI is one and a half times the carrier power. For maximum modulation conditions, therefore, only one-third of the total power is contained in the sidefrequencies. Since it is the sidefrequencies that carry the intelligence, amplitude modulation is not a very efficient system when ~~!C"!(t on a power basis. EXAMPLE 1.4 The power dissipated by an amplitude-modulated wave is 100 W when...
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...FC demodulation can be performed using a receiving USRP. 3b) Using GNURadio Companion and a transmitting USRP, AM DSB FC modulation can be performed on a message signal with frequency 1 kHz and amplitude of one unit. The following code in Fig. 6 has been used to perform such a modulation with a transmitting USRP. Fig. 6 GNURadio Companion code to perform AM DSB FC modulation on a cosinusoidal message signal using a transmitting USRP. The modulated signal from the transmitting USRP is then received by a second USRP, which demodulates the signal, to obtain a signal whose waveform is comparable to that of the original message signal. Fig. 7 shows the code used on a receiving USRP to...
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...8/25/2013 Analog Communication MODULATION 1 8/25/2013 Introduction Topics to be covered • Need for Modulation • What is Modulation? • Types of Modulation • Amplitude Modulation (AM) • Angle Modulation • Frequency Modulation (FM) • Phase Modulation (PM) 2 8/25/2013 Baseband vs Passband Transmission • Baseband Signal:- Information bearing Signal or Message Signal. • The term Baseband refers to the band of frequencies representing the original signal obtained from the source (or Base). – Voice (0-4kHz) – TV (0-6 MHz) • A signal may be sent in its baseband format when a dedicated wired channel is available. • Otherwise, it must be converted to passband. Need for Modulation • Size of the antenna • For efficient radiation, the size of the antenna should be λ/10 or more (preferably around λ/4 ), where λ is the wavelength of the signal to be radiated. • Easy to Multiplex • Several message signals can be transmitted on a given channel, by assigning to each message signal an appropriate slot in the channel. • Channel Selectivity • Each station can be assigned a suitable carrier so that the corresponding program material can be received by tuning to the station desired. 3 8/25/2013 Need for Modulation • Improved Signal to Noise Ratio • Will be dealt in future lectures • Less Fading of transmitted signal • As the energy of a signal is proportional to its frequency, fading by the atmospheric particle is less What is Modulation...
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...CEEN 3250 Communication Systems Dr. Jang LAB REPORT EXPERIMENT #11: Amplitude Modulation (AM) using an Operational Transconductance Amplifier Rance Fredericksen LAB Partners Whouji Lo Ryan Leudders Date: April 3, 2007 University of Nebraska – Lincoln Peter Kiewit Institute OBJECTIVE 1. To become familiar with the 3080E operational transconductance amplifier (OTA) and how its variable gain feature makes it ideam for use as an AM modulator. 2. To observe typical AM waveforms that exhibit undermodulation, overmodulation, and 100% modulation. 3. To understand how a peak detector functions to extract the original intelligence from an AM waveform. PRELAB None. PROCEDURE First, we built the circuit shown here: Figure 11.1. AM Circuit Schematic. In order for the non-inverting input of the Operational Amplifier to be exactly ZERO VOLTS, the variable resistor (shown on the left-hand side of Figure 11.1) was set to 5.6k/4.4k. The switch shown on the bottom left corner of the diagram was set initially to position 1 (ground). Once this circuit was constructed, we applied a 60mVp-p sine wave at the input. At the output (Vo), we observed a sinusoid, and we again adjusted the variable resistor to obtain a ZERO VOLT DC OFFSET. We then moved the switch to POSITION 2. Once in position 2, we took measurements of amplifier gain while adjusting the variable resistor (on the right-hand side of Figure 11.1) between its extremes...
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...is to learn the principles of amplitude modulation and to observe the outcome when the two signals are mixed. Basically in this experiment we were trying to explore and study about amplitude modulation. Amplitude modulation is used in electronic communication and is commonly used for transmitting information or messages by a radio carrier wave. I find this experiment very useful to us because it will further enhance our learning and will acquaint us more on what we are able to discuss in our lecture class about amplitude modulation. The experiment is very short yet we were able to learn more and were able to see an actual waveform generated which supports the lessons that we have learned from our lecture classes. I might say that so far this is the only experiment that we were able to finish it with complacency. During the first part of our experiment we were trying to get the expected waveform of a modulated signal using the ECE21 board #1 and ECE21 board #4.We tried to adjust the frequencies of the signal generator and its amplitude which is 3 Vpp to get the expected waveform. Once the waveform is obtain, we then compute the percent modulation of the circuit using the Vmax and the Vmin of the waveform obtained and displayed in our oscilloscope. We tried to decrease the amplitude of the panel generator to zero and was able to notice that it will result to a small amplitude and a non-modulated signal. We also tried to increase the amplitude of the signal until we can obtain...
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...1 |(a) |A music signal with frequency components from 50 Hz to 21000 Hz is Frequency modulated. If the maximum allowed frequency deviation is 50 kHz i) What is the modulation index? ii) What is the signal bandwidth using Carson’s rule? | | |[10 Marks] | |2 |(a) |Draw the block diagram for a Superheterodyne Receiver | |[10 Marks] | |3 |(a) |Explain the operation of the Superheterodyne Receiver | |[10 Marks] | |4 |(a) |The five basic characteristics that determine the quality of a receiver are Selectivity, Sensitivity, Signal to noise ratio, | | | |Stability and Fidelity. Explain what is meant by any three of these. | |[10 Marks] | |5 |(a) |A 200 MHz carrier is frequency modulated by a 10 V peak-to-peak...
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...Introduction In this lab session we are going to study the SSBSC modulation and demodulation. The SSBSC is a shortage for Single Sideband Suppressed Carrier. It transmits only a one sideband, so that it cannot transmit both of the sum and the difference of frequencies. One advantage of the SSBSC is that it requires only half the bandwidth of the DSBC and AM. Equipment * Emona Telecom-Trainer 101 * Dual Channel 20MHz oscilloscope * Two Emona Telecom-Trainer 101 oscilloscope leads * Assorted Emona Telecom-Trainer 101 Patch Leads Procedure Part a: Generating an SSBSC signal using a simple message We start by doing the connection by the following steps: * First, we make sure that the Trigger Source control is set to the CH 1 position. * Then we set the scope mode control to the DUAL position. * We insert the black plugs of the Oscilloscope into a ground, and we followed the schematic shown in Figure 1 to implement the connection shown in figure 2. Figure [ 1 ] Figure [ 2 ] First implementation * Later we adjust the scope's Time base control to view two or more cycles of the two message signals. * We set the phase shifter module's Phase Change control to the 180° position, and we set the Phase Adjust to the middle of its travel. * We followed the schematic shown in Figure 3 to do the implementation shown in Figure 4. Figure [ 3 ] Figure [ 4 ] * We used the scope to check that the lower Multiplier module's...
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...n Analog Technology, Compare and Contrast the Advantages and Disadvantages of Amplitude Modulation, Frequency Modulation, Phase Modulation, and Quadrature Amplitude Modulation Advantages and disadvantages of the following analog modulation techniques: In analog technology, compare and contrast the advantages and disadvantages of amplitude modulation, frequency modulation, phase modulation, and Quadrature Amplitude Modulation Amplitude Modulation When dealing with communication modulation is the process of altering one or more of the three primary parameters of a message signal. Modulation of message signals allow for the signal to be imbedded into a carrier signal that can be physically transmitted. The three primary parameters are amplitude, frequency, and phase. When dealing with analog modulation techniques each one that is used will have advantages and disadvantages. The amplitude modulation (AM) technique is based on the transformation of the highs and lows of a signal wave or its strength. This technique has the advantages of being able to travel long distances by bouncing off of structures as well as the atmosphere. The main disadvantage of this modulation technique is that is highly susceptible to signal interference from other electronic devices and waves creating and unclear signal, these interferences are what is known has noise. Frequency modulation (FM) is that of what its names says it is the altering of the frequency of a baseband signal. Altering...
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...Noise may be defined as any unwanted form of energy tending to interfere with the proper and easy reception and reproduction of signals. It may be subdivided according to type, source, effect, relation to the speaker, depending on circumstances. 1. External Noise. * Atmospheric Noise – consist of spurious radio components distributed a wide range of frequencies. Majority of these radio signals come from the natural sources of disturbance generally called static. * Extraterrestrial Noise * Solar Noise * Cosmic Noise * Industrial Noise – the intensity of noise made by humans easily outstrips that created by any other source, internal or external to the receiver. 2. Internal Noise * Thermal agitation noise – it is due to the rapid and random motion of molecules, atoms and electrons of which any such resistor is made up. Vn = 4kTδƒ R Example a. An amplifier operating the frequency rate from 18 to 20 MHz has a 10-kΩ input resistor. What is the rms noise voltage at the input to this amplifier if the ambient temperature is 27° C? Vn = 4kTδƒ R =4 x 1.38 x 3 x 2 x 10-11 = 1.82 x 10-5 = 18.2 μV * Shot noise – it is caused by random variations in the arrival of electrons at the output electrode of an amplifying device and thus as a randomly varying noise current superimposed on the output. 1.6 x 10-19 C in =2eip δf * Transmit Time Noise – if the time taken an electron to travel from the emitter to...
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...friends told me that amplitude modulation (AM) was extinct. I was under the impression that SSB was the only mode of HF phone permitted. Later I learned that AM isn't actually illegal and there are a few diehards using AM on the 75 and 10 meter phone bands. I've also heard AM stations on 15 and 160 meters. In short, you might find a use for it. Besides, it's an interesting challenge to AM-modulate a transistorized transmitter. Homebuilt AM Back in the vacuum tube days many of us built our own transmitters and AM modulators. My first AM transmitter was a Heathkit DX-20. That was a 50 watt, CW, kit-built, vacuum tube transmitter to which I added a homebuilt AM modulator. Unlike SSB, AM could be added onto an existing CW transmitter. Rather than generate a low power AM signal and then amplify it with a linear amplifier, in the old days the usual method was to AM-modulate the final amplifier of the CW transmitter. On an oscilloscope, the hallmark of AM is that, when you are not speaking, the RF carrier wave runs continuously at an average power. That is, in AM the highest peak power and zero power only occur at the very highest voice peaks. Although I could see these transient peaks 2. Chapter 16, Harris on the scope, when I tried to catch one with a storage scope, they are statistically rare and I couldn't catch a zero power level. The waveform below was typical of what I saw. In contrast to AM, the RF output amplitude in SSB is always...
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...frequency is measured in hertz. Each hertz is equal to one cycle of an event in seconds. For a frequency to be considered an audio frequency it has to be between 15 Hz and 20000 Hz. A radio frequency will range from 20 kHz to 1 terahertz. A medium for radio frequency will be air and metal. Air will not conduct electricity so the displacement won’t happen. When it comes to infinity value, air will become resistant and only some current flow will go through. Metal is an electricity conductor. This means that the flow will be based on the resistance of metals and the components with in the metal. What is analogue modulation? Is the information which is applied to the carrier signal. This is usually with radio signals. The amplitude modulation will change any frequency of the signal. Frequency Modulation is the frequency of the Carrier can wave at the input signal with the level use multiple methods When comparing the modulation we can show that both use the same method. The only difference is that digit. While this process is going on the digital modulation can use multiple times. Digital will also apply filters to interfering data. The disadvantage is it will give communication References http://wiki.answers.com/Q/Write_two_separate_analogies_one_to_describe_each_of_the_following_principles_of_radio_wave_transmission_Frequency_What_if_your_analogy_must_explain_voltage_current_and_resistance_Analog_vs_digita...
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...Unit 2 Assignment 1 Blank Answer Sheet Name: Date: Electronics ET2530 Chapter 2 (pp. 111-113) 2. A 1500 kHz carrier and a 2 kHz intelligence signal are combined in a non-linear device. List all the frequency components produced. - 1498, 1500, and 1520KHz 3.If a carrier is amplitude modulated what causes the sideband frequencies? - The non-linear mixing of the carrier and intelligence frequencies. 4.What determines the bandwidth of emission for an AM transmission? - It is twice the frequency of the highest audio frequency transmitted. The upper sideband is fc +FM where fc is the carrier frequency and FM is the modulation (audio) frequency .The lower sideband is fc – FM. The total bandwidth is 2*FM 5.Explain the difference between a sideband and a side frequency. - A sideband carries the modulation or "information". in old fashioned AM and FM transmission schemes, a carrier is broadcast in addition to the sideband(s). Only the sideband is needed to communicate. A spurious frequency that happens when a carrier is transmitted has no added "information" and just adds to the transmission bandwidth. Sometimes these occur by intermixing within the transmitter. a common example is CB splatter from overdrive of RF amps. 9.Draw a diagram (or indicate which text book Figure # shows this) of a carrier wave envelope when modulated by 50% by a sinusoidal wave. Indicate on the diagram the dimension from which the percentage of modulation is determined. ...
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...Peter Vallejo Intro to Telecommunications September 30, 2015 Chapter 2 Amplitude Modulation: Transmission 1. A 1500-kHz carrier and 2-kHz intelligence signal are combined in a nonlinear device. List all the frequency components produced. 1498, 1500 and 1520kHz 2. If a 1500-kHz radio wave is modulated by a 2-kHz sine-wave tone, what frequencies are contained in the modulated wave (the actual AM signal)? 3. If a carrier is amplitude-modulated, what causes the sideband frequencies? The non-linear mixing of the carrier and intelligence frequencies. 4. What determines the bandwidth of emission for an AM transmission? It is twice the frequency of the highest audio frequency transmitted. The upper sideband is fc +FM where fc is the carrier frequency and FM is the modulation (audio) frequency. The lower sideband is fc-FM. The total band 10. What are some of the possible results of overmodulation? 19. Why is a high percentage of modulation desirable? 20. During 100 percent modulation, what percentage of the average output power is in the sidebands? (33.3%) 23. Describe two possible ways that a transistor can be used to generate an AM signal. 24. What is low-level modulation? 25. What is high-level modulation? 27. Why must some radio-frequency amplifiers be neutralized? 29. Define parasitic oscillation. Higher frequency self-oscillations in RF amplifiers. 30. How does self-oscillation occur? 32. What is the principal advantage of a class C amplifier? 35....
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...Advantages and disadvantages of the following analog modulation techniques: In analog technology, compare and contrast the advantages and disadvantages of amplitude modulation, frequency modulation, phase modulation, and Quadrature Amplitude Modulation Amplitude Modulation When dealing with communication modulation is the process of altering one or more of the three primary parameters of a message signal. Modulation of message signals allow for the signal to be imbedded into a carrier signal that can be physically transmitted. The three primary parameters are amplitude, frequency, and phase. When dealing with analog modulation techniques each one that is used will have advantages and disadvantages. The amplitude modulation (AM) technique is based on the transformation of the highs and lows of a signal wave or its strength. This technique has the advantages of being able to travel long distances by bouncing off of structures as well as the atmosphere. The main disadvantage of this modulation technique is that is highly susceptible to signal interference from other electronic devices and waves creating and unclear signal, these interferences are what is known has noise. Frequency modulation (FM) is that of what its names says it is the altering of the frequency of a baseband signal. Altering the number of times each second that the current changes direction; comes with the advantage of being less susceptible to noise unlike that of AM. Also unlike AM, FM is not...
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