Ec2306 mini project report-matlab
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  • 1. AM RECEIVERVini Narayanankutty (11509106086), Subhrata Sarangi (11509106074), Sangita S Nair (11509106056) Department of Electronics communication & engineering SRIRAM ENGINEERING COLLEGE, PERUMALPATTU PROJECT REPORT EC2306 Digital Signal Processing Lab Guided By K. Gayathri Lecturer, ECE Date: 28/09/2011
  • 2. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056) ABSTRACT Our Term Project is to study and implement an AM RECEIVER based onSuper heterodyne principle virtually used in all modern radio and television receivers.Theapproach mainly involves the use of heterodyning or frequency mixing. The signal from theantenna is filtered sufficiently at least to reject the image frequency (see below) and possiblyamplified. A local oscillator in the receiver produces a sine wave which mixes with thatsignal, shifting it to a specific intermediate frequency (IF), usually a lower frequency. The IFsignals is itself filtered and amplified and possibly processed in additional ways. Thedemodulator uses the IF signals rather than the original radio frequency to recreate a copy ofthe original modulation (such as audio). The project is coded in MATLAB.EC2306 Digital Signal Processing Lab Page 2
  • 3. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056) ACKNOWLEDGEMENTOur indebted thanks to our respected Dean Prof V.Thyagarajan, to do this project work.We express our sincere thanks to our Head of the department, Mr.V.Salaiselvam M.E.(PhD) who has helped us to take this invaluable project. We express our sincere thanks toour guide Ms K.GAYATHRI, Lecturer ECE for the untiring continued technicalguidance during the fabrication and preparation of the Project. This is a major motivationforce for us to complete our project work.EC2306 Digital Signal Processing Lab Page 3
  • 4. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),Sangita Nair(11509106056) anankutty(11509106086),SubhrataSarangi(11509106074),SangitaS SRIRAM ENGINEERING COLLEGE Perumalpattu, Thiruvallur Taluk - 602024 (Approved by AICTE, Affiliated to Anna University Chennai and Accredited by NBA) REGISTER NO: 11509106086, 11509106074, 11509106056 MINI PROJECT REPORT 2011 – 2012Name of lab: EC2306 DIGITAL SIGNAL PROCESSINGDepartment: Electronics & Communication Engineering Certified that this is a bonafide record of work done by VINI NARAYANANKUTTY,SUBHRATA SARANGI, SANGITA S NAIR Of 3RD YEAR 5TH SEMESTER Class,having completed the Mini Project with his team members on the topic “AM RECEIVER”. “AMIn the DIGITAL SIGNAL PROCESSING LAB during the year 2011 – 2012.Submitted for the Demonstration held on: 28/09/2011 or 28Signature of Head of dept: Signature of lab-in-charge: lab charge:EC2306 Digital Signal Processing Lab Page 4
  • 5. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056) TABLE OF CONTENTS 1. Introduction 1.1 What is Modulation 1.2 What is Amplitude Modulation and Demodulation 1.3 Techniques for AM Receiver 2. Super heterodyne Receivers 2.1 Circuit for Super heterodyne Receiver 2.2 Local Oscillator Stage 2.3 Mixer Stage 2.4 Coupling Capacitor 2.5 Intermediate Frequency Transformer/Filter (IFT) 2.6 Detector Stage 2.7 Audio Amplifier Stage 3. Implementation 3.1 Design Description 4. Matlab Coding 4.1 Coding 4.2 Output 5. Conclusion 5.1Advantage of AM Receiver 5.2Application of AM Receiver 6. ReferencesEC2306 Digital Signal Processing Lab Page 5
  • 6. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056) INTRODUCTION A radio communication system is composed of several communications subsystems that give exterior communications capabilities. A radio communication system comprises a transmitting conductor in which electrical oscillations or currents are produced and which is arranged to cause such currents or oscillations to be propagated through the free space medium from one point to another remote there from and a receiving conductor at such distant point adapted to be excited by the oscillations or currents propagated from the transmitter. One desirable feature of radio transmission is that it should be carried without wires (i.e.,) radiated into space. At audio frequencies, radiation is not practicable because the efficiency of radiation is poor. However, efficient radiation of electrical energy is possible at high frequencies (>20 kHz). For this reason, modulation is always done in communication systems.EC2306 Digital Signal Processing Lab Page 6
  • 7. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056) 1.1 ModulationModulation is a technique for transferring information or message of lowerfrequency by riding it on the higher frequency carrier. In other words, the processby which some characteristic of a higher frequency wave is varied in accordancewith the amplitude of a lower frequency wave. This solves the major problem ofantenna size and signal distortion (or noise) in communication system. There aretwo types of modulation: 1. AM 2. FM 1.2 Amplitude modulation and demodulationThe basic idea of AM is that “vary the amplitude of carrier wave in proportion tothe message signal. For this purpose message is multiplied with a sinusoidal offrequency ωο. The highest frequency of the modulating data is normally less than10 percent of the carrier frequency. The instantaneous amplitude (overall signalpower) varies depending on the instantaneous amplitude of the modulating data.Figure below shows an AM signal. Figure 1: (a) Carrier signal. (b) Message (c) AM signalEC2306 Digital Signal Processing Lab Page 7
  • 8. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056)Demodulation is the reverse of modulation that is a process for retrieving aninformation signal that has been modulated onto a carrier. 1.3 AM ReceiverFor extracting the message signal back from the carrier wave we demodulate theRF signal. For AM demodulation we have different methods:1.3.1 Tuned RF Receivers1.3.2 Regenerative ReceiversEC2306 Digital Signal Processing Lab Page 8
  • 9. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056)1.3.3 Super-Regenerative Receivers1.3.4 Super-heterodyne ReceiversWe here concentrate on design of Super heterodyne ReceiverEC2306 Digital Signal Processing Lab Page 9
  • 10. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056) 2. SUPER HETERODYNE RECEIVERSThe concept of heterodyning an incoming signal to convert it to a lower frequencywas developed by Armstrong and others in 1918.Armstrongs original design,shown in Figure, was intended to allow low frequency radiotelephone receivers tobe adapted for use at newer HF frequencies being used in Europe. Figure 3: Original Super heterodyne design 2.1 Advantages of Super heterodyne Receiver 1 . The low-frequency receiver (typically a high quality tuned-RF design) could be adjusted once, and thereafter all tuning could be done by varying the heterodyne oscillator. 2 . Amplification could be provided primarily at a lower frequency where high gains were easier to achieve. Amplification was split between two frequencies, so that the risk of unwanted regenerative feedback could be reduced. 3 . Narrow, high-order filtering was more easily achieved in the low frequency receiver than at the actual incoming RF frequency being received.Eventually, the separate tuned-RF receiver was replaced by the dedicated IFsection of the modern super heterodyne design, in which pre-tuned fixed-frequencyfilters, are employed. The result became the well-known architecture used todaywith high quality channel-select filtering and no adjustments aside from volumeand tuning controls.EC2306 Digital Signal Processing Lab Page 10
  • 11. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056)Two demodulation techniques are used with super heterodyne receivers,Synchronous and Asynchronous.We will stick to only with Asynchronous Super heterodyne model. Below in thefigure is shown a more general block diagram of super heterodynereceiver.EC2306 Digital Signal Processing Lab Page 11
  • 12. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056) 2.2 Circuit for Super heterodyne ReceiverAlthough super heterodyne radio receivers look not very complicated but forpracticable purposes there must be additional circuitry involved in the design. Oneof them is Automatic Gain Control (AGC).The AGC circuit keeps the receiver inits linear operating range by measuring the overall strength of the signal andautomatically adjusting the gain of the receiver to maintain a constant level ofoutput. When the signal is strong, the gain is reduced, and when weak, the gain isincreased, or allowed to reach its normal maximum..For simplicity of circuit, we will present a circuit without AGC. The completecircuit given below appears to be complicated, that is why we have decided toexplain it systematically.EC2306 Digital Signal Processing Lab Page 12
  • 13. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056) 2.3 Components Local Oscillator Stage Mixer Stage Coupling Capacitor Intermediate Frequency Transformer/Filter (IFT) Detector Stage Audio Amplifier Stage 2.3.1 Local Oscillator StageIn most of AM receivers, local oscillator (LO) is designed withthe help of a special component, known as oscillator coil. Theircore is movable between the coils. The main purpose of havinga moveable core is to tune the oscillator at desire band. Thetop side of LO is colored white in order to distinguish it fromintermediate frequency transformers. They come in metalhousing and there are five pins plus two pins of metal housing.The pin configuration of LO is shown in figure 7. Figure 7: Three different views of LOEC2306 Digital Signal Processing Lab Page 13
  • 14. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056) 2.3.2 Mixer StageMultiplying the RF signal from the antenna with the frequency of LO is anessential part of demodulation. IC NE612 is used here, because it takes very littlepower from input signal, the quality of mixing is very good and output signal isvery much close to the intermediate frequency (IF), it has its own voltage regulatoras for mixer circuit the supply voltage should be very constant. And the biggestadvantage is that its use is very simple, attach antenna to pin 1 or 2, ground pin no.3 and 6 volt to pin no.8. Then connect LO between pin 6 and 7, and get IFfrequency out from pin 4 and 5.Figure 9: Block Diagram and pin configuration of NE612 2.3.3 Coupling CapacitorAs we know that in super heterodyne design our RF stage and LO should oscillatein such a way that their difference is always 455 kHz (IF frequency). In order toget simultaneously tuning of both circuits, we use coupling capacitor. They are justpair of two capacitors connected parallel to each other. One is for main tuning andother is for fine-tuning. In the case of FM, there are four capacitors. There blockdiagram and pin configuration is shown bellow.EC2306 Digital Signal Processing Lab Page 14
  • 15. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056) 2.3.4 Intermediate Frequency Transformer/Filter (IFT)Intermediate frequency filter is made with the help of transformer similar to the LOstage, so it is called IFT. They too came in metal housing as LO. The onlydifference is that they also have a capacitor built in them. The capacitor can beseen in the following figure.Figure 10: Details and pin description of IF FilterAs you can see it in figure, the IFT is, in fact, a parallel oscillatory circuit with aleg on its coil. The coil body has a ferrite core (symbolically shown with singleupward straight dashed line) that can be moved (with screwdriver), which allowsfor the setting of the resonance frequency of the circuit, in our case 455 kHz. Thesame body contains another coil, with fewer quirks in it. Together with the biggerone it comprises the HF transformer that takes the signal from the oscillatorycircuit into the next stage of the receiver. Both the coil and the capacitor C areplaced in the square-shaped metal housing that measure 10x10x11 mm. From thebottom side of the housing you can see 5 pins emerging from the plastic stopper,that link the IFT to the PCB, being connected inside the IFT. Besides them, thereare also two noses located on the bottom side, which are to be soldered andconnected with the device ground. Japanese IFTs have the capacitor C placed inthe cavity of the plastic stopper, as shown in figure. The part of the core that can bemoved with the screwdriver can be seen through the eye on the top side of thehousing, figure 10-d. This part is colored in order to distinguish the IFTs betweenthemselves, since there are usually at least 3 of them in an AM receiver. The colorsare white, yellow and black (the coil of the local oscillator is also being placed insuch housing, but is being painted in red, to distinguish it from the IFT).EC2306 Digital Signal Processing Lab Page 15
  • 16. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056) 2.3.5 Detector StageThe detector stage is implemented with the easiest method that is with envelopdetection. No description is necessary, only the circuit is given below. Please notethat this method is known asynchronous detection. 2.3.6 Audio Amplifier StageIn order to get good and loud voice from the speaker it is essential to have an audiofrequency (AF) amplifier or simply audio amplifier. For this purpose well-knownaudio amplifier IC LM386 is used. It is low priced and good quality IC. We can get20 to 200times amplification from it. Pin 5 gives the output, which in turn isconnected with the loudspeaker. The speaker should be round about 10 rated to1W. If speaker is not available just omit the LM386 and place a headphone justafter the detector. Figure 11: Audio AmplifierEC2306 Digital Signal Processing Lab Page 16
  • 17. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056) 3. IMPLEMENTATIONSuper heterodyne Receivers can be implemented in different ways namely 1. Modern Single Conversion Implementations 2. Multiple Conversion Implementations 3. Up Conversion Implementations 4. Designs with Ultra-Low IFs 5. Designs with Image Rejection Mixers 6. Designs with Selective Demodulators 3.1 Design DescriptionWe go with simple super heterodyne receiver with image rejection mixers. Wehere simulate the operation of the heterodyne section and demodulating section ofa AM receiver. An array is created that represents the superposition of threeseparate RF carriers, each modulated at a different audio frequency. This is thekind of signal that could be expected at the output of the LNA. This signal ismultiplied by a local oscillator, passed though an IF filter, and demodulated using asimple envelope detector (half-wave rectifier and single pole LPF). Some plots arecreated at the end to show the signal at various locations in the receiver.EC2306 Digital Signal Processing Lab Page 17
  • 18. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056) 4. MATLAB CODINGThis m-file simulates the operation of the heterodyne section and demodulatingsection of a garden variety AM receiver. An array is created that represents thesuperposition of three separate RF carriers, each modulated at a different audiofrequency. This is the kind of signal that could be expected at the output of theLNA. This signal is multiplied by a local oscillator, passed though an IF filter, anddemodulated using simple envelope detector (half-wave rectifier and single poleLPF). Some plots are created at the end to show the signal at various locations inthe receiver.REQUIREMENT: The Signal Processing Toolbox and Control System Toolboxare needed to run this file because of the function calls to butter (), tf(),and c2d(). Itis possible that this file could be modified to avoid using those three functions bydetermining the filter coefficients differently in MATLAB or calculating themusing another program, lookup table, etc. and entering them manually. 4.1 Coding% StartClear all;Close all; % Clear memory and close figures, files, etc.% RF sectionFc = [700 750 800]*1e3; % Carrier frequencies (Hz)Ac = [1.00 1.25 1.50]; % Carrier amplitudesFm = [1 2 3]*1e3; % Modulation frequencies (Hz)Dm = [0.25 0.25 0.25]; % Modulation depthsEC2306 Digital Signal Processing Lab Page 18
  • 19. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056)Fs = 20*max(Fc); % Sample rate, 20 times the highest RF (Hz)Ts = 1/Fs; % Sample period (s)L = 10/min(Fm); % Duration of signal, 10 times the period of % the lowest modulation frequencyt = Ts*(0:ceil(L/Ts)-1); % Array of sample times (s)Sc = diag(Ac)*cos(2*pi*Fc*t); % Carrier signals. A three row array with % each row representing a single RF % carrier.Sm = 1 + diag(Dm)*cos(2*pi*Fm*t); % Modulating signals. A three row array % with each row representing the % modulation for a single carrier.Stx = sum(Sm.*Sc, 1); % RF signal. The superposition of three separately % modulated carriers. This is the type of signal % that could be expected at the output of the LNA % (or input to the mixer).% Mixer sectionFLO = 300e3; % Local oscillator frequency (Hz)ALO = 1; % Local oscillator amplitudeSLO = ALO*cos(2*pi*FLO*t); % Local oscillator signalSmix = Stx.*SLO; % Signal at the output of the mixer% IF filter sectionWe have generated a continuous time transfer function for a Butterworth band passfilter and then converted that to its discrete Equivalent.EC2306 Digital Signal Processing Lab Page 19
  • 20. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056)[NUM,DEN] = butter (5, [2*pi*430e3 2*pi*470e3],’s’); %Filter coefficients for a 10th order Butterworth band pass centered at 450 MHzHd = c2d(tf(NUM, DEN), Ts); % Discrete equivalent derived from previous continuous time filter coefficientsSfilt = filter(Hd.num{1}, Hd.den{1}, Smix); % Signal at the output of the IF filter% Envelope detector sectionSrect = Sfilt; Srect(Srect<0) = 0; % Half-wave rectified IF signaltau = 0.1e-3; % Filter time constant (s)a = Ts/tau;Srect_low = filter (a, [1 a-1], Srect); % Low pass filtering to recover the modulating signal% Plotting section% the plots display numerical data from somewhere in middle of the arrays so thatthe transient responses from the filters have had a chance to ring out. Each figurecontains three plots: the RF signal, the IF filter output, and the demodulated audiosignal. The first figure plots a longer segment of time so the demodulated audiosignal can be distinguished. The second figure plots a much shorter segment oftime to show the detail in the RF signal.figure;min_index = ceil(length(t)/2);max_index = min_index + ceil(2/min(Fm)/Ts);subplot(3,1,1);plot(t(min_index:max_index), Stx((min_index:max_index)));EC2306 Digital Signal Processing Lab Page 20
  • 21. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056)xlim([t(min_index) t(max_index)]); xlabel(Time (s));subplot(3,1,2);plot(t(min_index:max_index), Sfilt((min_index:max_index)));xlim([t(min_index) t(max_index)]); xlabel(Time (s));subplot(3,1,3);plot(t(min_index:max_index), Srect_low((min_index:max_index)));xlim([t(min_index) t(max_index)]); xlabel(Time (s));figure;min_index = ceil(length(t)/2);max_index = min_index + ceil(150/min(Fc)/Ts);subplot(3,1,1);plot(t(min_index:max_index), Stx((min_index:max_index)));xlim([t(min_index) t(max_index)]); xlabel(Time (s));subplot(3,1,2);plot(t(min_index:max_index), Sfilt((min_index:max_index)));xlim([t(min_index) t(max_index)]); xlabel(Time (s));subplot(3,1,3);plot(t(min_index:max_index), Srect_low((min_index:max_index)));xlim([t(min_index) t(max_index)]); xlabel(Time (s));EC2306 Digital Signal Processing Lab Page 21
  • 22. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056) 4.2 OutputEC2306 Digital Signal Processing Lab Page 22
  • 23. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056)EC2306 Digital Signal Processing Lab Page 23
  • 24. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056) 5. CONCLUSION 5.1 Advantages of AM Receiver Easy to produce in a transmitter Simple in design. AM is simple to tune on ordinary receivers, and that is why it is used for almost all shortwave broadcasting. 5.2 Application of AM Receiver Short wave Broadcasting A geographic information management system (GIS) is applied to perform the automated mapping and facility management (AM/FM) of power distribution systems for contingency load transfer. Contingency load transfer for distribution system operation can be enhanced significantly with the application of AM/FM systems to determine the switches to be operated and the corresponding spatial locations of the switches.EC2306 Digital Signal Processing Lab Page 24
  • 25. AM ReceiverViniNarayanankutty(11509106086),SubhrataSarangi(11509106074),SangitaS Nair(11509106056) 6. REFERENCES 1. Wikipedia-Radio receiver 2. Numerical computing with MATLAB by Cleve B. Molar. 3. MATLAB demystified By David McMahonEC2306 Digital Signal Processing Lab Page 25