ADVANCED COMMUNICATION LAB MANUAL
CANARA ENGINEERING COLLEGE Benjanapadavu, Mangalore-574219 Subject Code: 10ECL67 ADVANCED COMMUNICATION LAB MANUAL DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING Advanced Communication Laboratory The Advanced Communication Laboratory covers design and verification of the concepts of modern digital communication systems that operates from MHz-GHz range. The lab include experiments on applications of Digital coding and modulation techniques, Fiber Optic Communication, and Characteristics of microwave waveguide components. This lab is equipped with Oscilloscopes, Function Generators, Modules for Digital Modulation and Demodulation techniques and Power Supply units. To enhance precise measurement and observe waveform with better clarity Digital Storage Oscilloscopes are used. The Microwave test benches are used to conduct experiments in GHz frequency range. Various digital coding and modulation kits are used apart from discrete components to demonstrate the basic concepts involved in digital communication. An OFT kit is used to demonstrate communication and multiplexing through Light waves. i Objectives Introduction to design and verification of the concepts of modern digital communication systems that operates from MHz-GHz range Simplified practical illustrations of various Digital Modulation and Demodulation techniques Exposure to the challenges and characteristics of communication over an OFC channel Introduction to basic antenna types and their radiation patterns Introduction to the fundaments of microwave communication and challenges ii Outcomes Understand the microwave signal measurement using VSWR and frequency meter Understand the design, application and practical implementation of various Digital Modulation techniques. Understand the challenges in practical implementation of Microwave Communication Systems Understand the characteristics of various antennae and its coverage area Understand the characteristics and various losses associated with OFC channel Understand the various elements involved in the Physical Layer of the modern communication systems. iii Courses Related to Laboratory 1. 10EC61: Digital Communication 2. 10EC64: Antennas and Propagation 3. 10EC54: Microwaves and Radar 4. 10EC72: Optical Fiber Communication Lab Equipment Oscilloscopes o CROs- Two Channel o DSOs- Two Channel and Four Channel Signal Generators Dual Regulated Variable Power Supplies TDM Trainer Kit Digital Communication Trainer Kits: ASK, FSK, PSK, DPSK, and QPSK Kits VSWR Meter Microwave signal generators Simple Dipole and Folded Dipole Antenna trainer kit Printed Dipole, Microstrip Patch antenna and Yagi antenna (printed) trainer kit Microstrip Directional Coupler, Ring Resonator and Power Divider OFC Trainer kits Microwave Test Bench (using Klystron) PCM CODEC kit Component Tester Breadboards and Soldering Boards Digital Multimeters Analog and Digital ammeters and voltmeters iv LIST OF EXPERIMENTS Sl. No. Page No. Name of the Experiment 1 Time Division Multiplexing and Demultiplexing of two band limited signals 1 2 Amplitude Shift Keying Modulation and Demodulation 3 3 Frequency shift keying Modulation and Demodulation 8 4 Phase Shift Keying Modulation and Demodulation 12 5 Differential Phase Shift Keying Modulation and Demodulation 15 6 Quadrature Phase Shift Keying Modulation and Demodulation 18 7 Measurement of frequency and power in a microwave test bench using Klystrone 21 8 Study of Propagation loss, Bending loss and Measurement of Numerical Aperture in OFC 25 9 Determination of coupling and isolation characteristics of a microstrip directional coupler 30 10 (a) Measurement of resonance characteristics of a microstrip ring resonator and determination of dielectric constant of the substrate. (b) Measurement of power division characteristics of a microstrip 3 dB power divider. 32 11 Study Of Dipole Antenna Radiation Pattern ( Simple Dipole and Folded Dipole antenna) 35 12 To find the Gain and Directivity of Yagi-Uda Antenna, Dipole antenna and Patch antenna 40 13 Analog and Digital communication link using optical fiber 45 14 PCM generation and detection using a CODEC Chip 49 Bibliography 53 VIVA QUESTIONS 54 v Advanced Communication Lab Manual-10ECL67 Expt No-1. TIME DMSION MULTIPLEXING (TDM) AIM: To design and demonstrate the working of TDM and recovery of two band limited signals of PAM signals. Components Required: Transistors-SL-lOO, SK-lOO, Resistors- 1 kΩ, 1.5 kΩ, OpAmp µA 741. THEORY: TDM is a technique used for transmitting several message signals over a communication channel by dividing the time frame into slots, one slot for each message signal. This is a digital technique in which the circuit is highly modular in nature and provides reliable and efficient operation. There is no cross talk in TDM due to circuit nonlinearities since the pulses are completely isolated. But it also has its disadvantages, which include timing jitter and synchronization is required. In pulse-amplitude modulation, the amplitude of a periodic train of pulses is varied in proportion to a message signal. TDM provides an effective method for sharing a communication channel. CIRCUIT DIAGRAM: Dept. of E&C, Canara Engineering College, Mangalore. Page 1 Advanced Communication Lab Manual-10ECL67 Expected Waveforms: Procedure 1. Rig up the circuit as shown in the circuit-diagram for multiplexer. 2. Feed the input message signals ml and m2 of 2 volts P-P at 200 Hz. 3. Feed the high frequency carrier signal of 2V (P-P) at 2 kHz. 4. Observe the multiplexed output. 5. Rig up the circuit for demultiplexer. 6. Observe the demultiplexed output in the CRO. RESULTS: CONCLUSION: Dept. of E&C, Canara Engineering College, Mangalore. Page 2 Advanced Communication Lab Manual-10ECL67 Expt No-2. AMPLITUDE SHIFT KEYING MODULATION AND DEMODULATION AIM: To design and verify the operation of ASK generator and demodulator. Components Required Transistor SLlOO,Resistors-4.7 kΩ, 20 kΩ (pot), 10 kΩ (pot), OpAmp ].1A741, DiodeBy127. THEORY: CIRCUIT DIAGRAM: Dept. of E&C, Canara Engineering College, Mangalore. Page 3 Advanced Communication Lab Manual-10ECL67 EXPERIMENTAL PROCEDURE: Procedure 1. Rig-up the modulator circuit as show in the figure. 2. Set the message signal of amplitude 10 V(P-P) and frequency 500 Hz. 3. Set the carrier signal of amplitude 2 V(P-P) and frequency 2 kHz. 4. Observe the ASK waveform at the collector of transistor. 5. Now connect the demodulation circuit. 6. Observe the demodulated output on the CRO. Procedure for ASK Kit ASK MODULATOR: A 4052 multiplexer is used as an ASK modulator. This is 2 to 1 multiplexer. For one input carrier is applied directly and for the second input the carrier is given by resistive attenuator of 2:1 ratio Data signal is given to select line of 2:1 mux. ASK DEMODULATOR: A detector and a low pass filter with a cutoff frequency of 3.4 kHz is used to demodulate the ASK signal. The output of lowpass filter is given to an opamp comparator. The output of comparator is original data transmitted. POWER SUPPLIES: Built in ±12V & ±5V at 350mA.Fixed DC power supplies are provided. CARRIER SIGNAL GENERATOR: An 8038 IC Based sine wave generator is provided as a carrier generator of frequency 7 kHz to 100 kHz variable. Dept. of E&C, Canara Engineering College, Mangalore. Page 4 Advanced Communication Lab Manual-10ECL67 BIT CLOCK GENERATOR: The Bit clock generator is designed using timer 555 which is operated in astable mode. The frequency of clock is chosen from 150Hz to 13 kHz. 8 BIT WORD GENERATOR: The 8 bit parallel to serial shift IC 74165 is used to generate the required word pattern. A set of DIP switches are used to set 1 and 0 pattern. The last stage output Q& is coupled to the first stage input Do in the shift register. The 8 bit data set by the switches and loaded with the register parallel is now shifted EXPERIMENTAL PROCEDURE: 1. Connect the AC Adaptor to the mains and the other side to the experimental trainer. 2. Observe the Bit Clock frequency on the Oscilloscope. Adjust the frequency to 10 KHz and connect it to Pin No. 2 of 74165 IC. 3. Set the SPDP switches pattern to the desired code (say 0000 1111). 4. Parallel load by changing the switch to opposite side to shift side for a short duration and get back to shift position. 5. Observe the 8 Bit word pattern at the output of the 8 Bit word generator. This is the actual modulating signal. 6. Adjust the carrier frequency of 100 KHz and 5 Volt p-p, give this input to the ASK modulator inputs using a patch chord. 7. Connect the 8 Bit word generators output to the data input terminal of the ASK Modulator. 8. Observe the data input on one channel on a CRO and ASK output on the second channel. 9. To get demodulated signal, connect the ASK modulator output to demodulator input. 10. Adjust the two knobs simultaneously to get the original digital message at the demodulator output on a CRO. Dept. of E&C, Canara Engineering College, Mangalore. Page 5 Advanced Communication Lab Manual-10ECL67 CIRCUIT DIAGRAM: TABULAR COLUMN: amplitude & Modulating Modulated Demodulated frequency of signal signal signal amplitude & data sent amplitude & amplitude & frequency frequency frequency 1. 2. 3 Dept. of E&C, Canara Engineering College, Mangalore. Page 6 Advanced Communication Lab Manual-10ECL67 EXPECTED WAVEFORMS: RESULTS: CONCLUSION: Dept. of E&C, Canara Engineering College, Mangalore. Page 7 Advanced Communication Lab Manual-10ECL67 Expt No-3. FREQUENCY SHIFT KEYING MODULATION & DEMODULATION AIM: To design and verify the operation of FSK generator and detector. Components Required: Transistor-SLlOO, SKIOO, Resistors, Capacitors. THEORY: FSK is one of the digital modulation technique. Here frequency of the carrier is switched between two values. A sinusoidal of amplitude' A' and frequency fc1 is used to represent a binary '1' and frequency fc2 is used to represent binary '0'. FSK modulated waveform can be represented as, Dept. of E&C, Canara Engineering College, Mangalore. Page 8 Advanced Communication Lab Manual-10ECL67 CIRCUIT DIAGRAM: EXPERIMENTAL PROCEDURE: 1. Rig up the modulator circuit as shown in the figure. 2. Apply carrier of amplitude 2 V(P- P) and frequency 1 kHz. 3. Apply carrier of amplitude 2 V(P- P) and frequency 2 kHz. 4. Apply message signal of amplitude 10 V(P - P) and frequency of 250 Hz. . 5. Observe ASK outputs at each collector of transistor, and also observe FSK output at pin 6 of op-amp. 6. Connect demodulator circuit. 7. Observe the demodulated output on CRO. Dept. of E&C, Canara Engineering College, Mangalore. Page 9 Advanced Communication Lab Manual-10ECL67 PROCEDURE for FSK kit: 1. Connect the AC Adaptor to the mains and the other side to the Experimental Trainer. 2. Apply any one Data output of the Decade Counter (7490 IC) to the Data input point of the FSK Modulator and observe the Same Signal in one Channel of a Dual Trace Oscilloscope. 3. Observe the output of the FSK Modulator on the second channel of the CRO. 4. During the Demodulation, Connect the FSK output to the input of the Demodulator. 5. Adjust the Potentiometers P1 and P2 until we get the Demodulated output equivalent to the Modulating Data Signal. CIRCUIT DIAGRAM: Dept. of E&C, Canara Engineering College, Mangalore. Page 10 Advanced Communication Lab Manual-10ECL67 TABULAR COLUMN: amplitude & Modulating Modulated Demodulated signal frequency of signal signal amplitude & frequency data sent amplitude & amplitude & frequency frequency 1. 2. 3 EXPECTED WAVEFORMS: RESULTS CONCLUSION Dept. of E&C, Canara Engineering College, Mangalore. Page 11 Advanced Communication Lab Manual-10ECL67 Expt No-4. PHASE SHIFT KEYING MODULATION & DEMODULATION AIM: To Study the operation of PHASE SHIFT KEY modulation and demodulation with help of Demonstration board THEORY: Fig shows the circuit diagram of the Phase Shift Key modulation and demodulation. In this carrier Generator is generated by a weinbridge oscillator around 28KHz. At ±5Vp-p sine wave using 741 IC. The sine wave is converted into square wave using TL084 in comparator mode. The transistor BC 107 converts the square wave signal to TTL level. This is used as a basic bit clock or 180º for a mark and 0º for space. This square wave is used as a clock input to a decade counter (IC7490) which generates the modulating data outputs. IC CD4051 is an Analog multiplexer to which carrier is applied with and without 180º phase shift to the two multiplex inputs of the IC. Modulating data input is applied to its control input. Depending upon the level of the control signal, carrier signal applied with or without phase shift is steered to the output. The 180º phase shift to the carrier signal created by an operational amplifier using 741 IC during the demodulation, the PSK signal is converted into a +5 volts square wave signal using a transistor and is applied to one input of an EX-OR gate. To the second input of the gate, carrier signal is applied after conversion into a +5 volts signal. So the EX-OR gate output is equivalent to the modulating data signal. EXPERIMENTAL PROCEDURE: 1. Switch ON the experimental board. 2. Apply the carrier signal to the input of the modulator 3. Apply the modulating data signal to the modulator input and observe this signal on channel 1 of the CRO 4. Observe the output of the PSK modulator on the channel 2 of the CRO 5. Apply this PSK output to the demodulator input and also apply the carrier input. 6. Observe the Demodulator output and compare it with the modulating data signal applied to the modulator input which is identical. Dept. of E&C, Canara Engineering College, Mangalore. Page 12 Advanced Communication Lab Manual-10ECL67 CIRCUIT DIAGRAM: TABULAR COLUMN: amplitude & Modulating Modulated Demodulated signal frequency of signal signal amplitude & frequency data sent amplitude & amplitude & frequency frequency 1. 2. 3 Dept. of E&C, Canara Engineering College, Mangalore. Page 13 Advanced Communication Lab Manual-10ECL67 EXPECTED WAVEFORMS: RESULTS CONCLUSION: Dept. of E&C, Canara Engineering College, Mangalore. Page 14 Advanced Communication Lab Manual-10ECL67 EXPT NO-5. DIFFERENTIAL PHASE SHIFT KEYING AIM: To Study the various steps involved in generating the Differential binary Signal and Differential Phase Shift Keyed Signal at the modulator end and recovering the binary signal from the received DPSK Signal. THEORY: The carrier wave signal is generated by a weinbridge oscillator around ***KHZ at ±5V P-P sine wave using 741 the sine wave is convert into square wave using TL084 in comparator mode. The Transistor BC 107 converts the square signal to TTL levels. This is used as a basic bit clock or 180° for a mark and 0° for space. This Square wave is used as a clock input to a decade counter(IC 7490) which generates the modulating data outputs. The modulation is performed as follows: The Differential signal to the modulating is generated using an Exclusive-OR gate(7486) and a 1-bit delay circuit using D flipFlop 7474 CD 4051 is an analog multiplexer to which carrier is applied with and without 180°degrees Phase shift(created by using an operational amplifier connected in inverting amplifier mode) to the input of the TL084.Differential signal generated by Ex-OR gate (IC 7486) is given to the multiplexer‟s control signal input. Depending upon the level of the control signal, carrier signal applied with or without phase shift is steered to the output. 1-bit delay generation of differential signal to the input is created by using a D-flip-flop(IC 7474). The demodulation is performed as follows: During the demodulation, the data and carrier are recovered through a TL084 op amp in comparator mode. This level is brought to TTL level using a transistor and is applied to one input of an EX-OR gate. To the second input of the gate, carrier signal is applied after conversion into a +5V signal. So the EX-OR gate output is equivalent to the differential signal of the modulating data. This differential data is applied to one input of an Exclusive-OR gate and to the second input, after 1-bit delay the same signal is given. So the output of this EX-OR gate is the recovered modulating signal. EXPERIMENTAL PROCEDURE: 1. „Switch ON‟ the experimental board. 2. Check the carrier Signal and the data generator signals initially. 3. Apply the carrier signal to the carrier input of the DPSK modulator and give the data generated to the data input of DPSK modulator and Bit clock output to Bit clock input of modulator. Observe the DPSK modulating output with respect to the input data generator signal of dual trace Oscilloscope (Observe the Dept. of E&C, Canara Engineering College, Mangalore. Page 15 Advanced Communication Lab Manual-10ECL67 DPSK modulating signal on channel 1 and the data generator signal on channel 2), and observe the DPSK signal with respective to Differential data also. 4. Give the output of the DPSK modulator signal to the input of demodulator, give the Bit clock output to the Bit clock input to the demodulator and also give the carrier output to the carrier input of demodulator. 5. Observe the demodulator output with respect to data generator signal ( Modulating Signal) CIRCUIT DIAGRAM: Dept. of E&C, Canara Engineering College, Mangalore. Page 16 Advanced Communication Lab Manual-10ECL67 TABULAR COLUMN: amplitude & Modulating Modulated Demodulated signal frequency of signal signal amplitude & frequency data sent amplitude & amplitude & frequency frequency 1. 2. 3 EXPECTED WAVEFORMS: RESULTS: CONCLUSION: Dept. of E&C, Canara Engineering College, Mangalore. Page 17 Advanced Communication Lab Manual-10ECL67 EXPT NO-6. Quadrature Phase Shift Keying (QPSK) AIM: To Study the Quadrature Phase Shift Keying. Equipments: Kit CT-13, Patch cards, Power supply and two-channel oscilloscope. THEORY: Digital Phase Modulation (or Phase Shift Keying - PSK) is very similar to Frequency Modulation. It involves changing the phase of the transmitted waveform instead of the frequency, these finite phase changes representing digital data. In its simplest form, a phase-modulated waveform can be generated by using the digital data to switch between two signals of equal frequency but opposing phase. Taking the above concept of PSK one stage further, it can be supposed that the number of phase shifts is not limited to only two states. The transmitted "carrier" can undergo any number of phase changes and by multiplying the received signal by a sine wave of equal frequency will demodulate the phase shifts into frequency independent voltage levels. This is, indeed the case in QPSK (Quadrature Phase Shift Keying, Sometimes this is known as quaternary PSK, quadriphase PSK, 4-PSK). With QPSK, the carrier undergoes four changes in 4 phases and can thus represent two bits of binary data. While this may seem insignificant at first glance, a modulation scheme has now been supposed that enables a carrier to transmit two bits of information instead of one, thus effectively doubling the bandwidth of carrier. QPSK has four phases and for a given bit-rate, the QPSK requires half the bandwidth of PSK and is widely used for this reason. BLOCK DIAGRAM: Dept. of E&C, Canara Engineering College, Mangalore. Page 18 Advanced Communication Lab Manual-10ECL67 EXPERIMENTAL PROCEDURE: Use CT-13 board. 1. Connect the power supply cable at the POWER IN connector and switch ON the power. 2. Connect the QPSK-TX to QPSK-RX. 3. Give the input through Dip switch S1 and observe the phase shift at QPSK-TX, compare the waveform with fig. 4. EX: Through the Dip switch select the bits as 11100100 (The switch is upper side=O, the switch is lower side= 1) 5. Change the bit pattern by using the Dipswitch and observe the corresponding changes at SLDATA-TX. 6. Demodulated output can be observed at SLDATA-RX at this point you will get the same pattern as that at SLDATA-TX and you can see the same at the 8-LEDs. 7. Ex: If your selected bit pattern is 11100100 then at the demodulation side LED D3, D4, D5 &D8 Should be ON and D6, 07, 09 & 010 should be OFF, Dept. of E&C, Canara Engineering College, Mangalore. Page 19 Advanced Communication Lab Manual-10ECL67 8. Note the delay between, SLDATA-TX and SLDATA-RX, There is 0.2 In sec delay. This is due to the delay between LT6/5-6(ISIG-QSIG)and U6/ I(SH/LD). Here first data is shifting and after 0.2 m sec the data is loading. Refer the following Fig: 9. If the LED's are not stable at the demodulator side then adjust the POT-P I(IPCK). 10. After power on if you are getting the wrong display (LED) at demodulator side then press SWI once you will get the same pattern as you set at the modulator side. EXPECTED WAVEFORMS: RESULTS: CONCLUSION: Dept. of E&C, Canara Engineering College, Mangalore. Page 20 Advanced Communication Lab Manual-10ECL67 EXPT NO-7. Measurement of frequency and power in a microwave test bench using Klystron AIM: 1. Plot 2 or 3 modes of the given Klystron tube 2. Obtain its Electronic Tuning Range (ETR) 3. Obtain its Electronic Tuning Sensitivity (ETS) 4. Demonstrate the mode on a CRO Experimental Setup: Block Diagram: KPS 2K25 Klystron Mount Isolator Variable Attenuator Frequency Meter Detector Mount CRO THEORY: The reflex klystron makes use of velocity modulation to transform a continues electron beam into microwave power. Electrons emitted from the cathode are accelerated and passed through the positive resonator towards negative reflector, which retards and finally, reflects the electrons and the electrons turn back through the resonator, suppose an rf field exist between the resonators the electrons traveling forward will be accelerated electrons leave the resonator at an the voltage at the Resonator changes in amplitude. The accelerated electrons leave the resonator at an increased velocity and the retarded electrons leave at the reduced velocity. The electrons leaving the resonator will need different time to return, due to change in velocities. As a result, returning electrons group together in bunches. As the bunches pass through Dept. of E&C, Canara Engineering College, Mangalore. Page 21 Advanced Communication Lab Manual-10ECL67 resonator, they interact with voltage at resonator grids. If the bunches pass the grid at such a time that the electrons are slowed down by the voltage then energy will be delivered to the resonator and Klystron will oscillate. The dimensions of resonant cavity primarily determine the frequency. Hence, by changing the volume of resonator, mechanical tuning of Klystron is possible. Also a small frequency change can be obtained by adjusting the reflector voltage. This is called Electronic Tuning. For further details refer Microwave Devices and Circuits by Samuel Y. Liao Important: Firing the Reflex Klystron EXPERIMENTAL PROCEDURE: 1. Set the cooling fan to be blow air across the tube. Set Beam voltage control knob fully anticlockwise (Off), Repeller voltage to 3/4 clockwise. Set modulation selector switch to AMMOD position. Keep AM-MOD amplitude knob and AM-FREQUENCY knob at mid-position. Volt/Current switch of the display to current position. Set display to read Beam voltage. 2. Wait for some 10 seconds; let the tube warm up and power supply get properly stabilized. 3. Slowly vary the beam voltage knob clockwise and set beam current to 19 or 20mA. The corresponding beam voltage would be around +290v. 4. Observe the demodulated square wave available at the detector o/p using a CRO. By adjusting the AM-MOD amplitude knob and the Reflector (repeller) voltage knob at a maximum o/p level on the CRO. During switch off power failure, bring down the beam current to 0 and follow steps 1&2 in the reverse order. Demonstrate the mode on a CRO: K P S – Klystron power supply. 1. Set up the equipment as shown in the fig. Keep the position of the variable attenuator at the minimum attenuation position. 2. Switch on the klystron power supply. 3. Adjust the beam voltage position around 290Volts. 4. By changing the repeller voltage any mode of the klystron can be seen on the oscilloscope. Plot o/p signal voltage v/s repeller voltage. The same can be obtained by plotting the o/p power v/s repeller voltage. Dept. of E&C, Canara Engineering College, Mangalore. Page 22 Advanced Communication Lab Manual-10ECL67 I Mode: Repeller Voltage (V) 60 65 70 Output Signal amplitude p-p Frequency in GHz Repeller Voltage (V) 95 100 105 Output Signal amplitude p-p Frequency in GHz II Mode: Modes of klystron Dept. of E&C, Canara Engineering College, Mangalore. Page 23 Advanced Communication Lab Manual-10ECL67 Calculations: 1. Mode Number: Knowing mode top voltage of two adjacent modes, mode number of the modes may be computed as given below. N2 N1 V1 V2 n 1 34 n 3 4 2. ETR(Electronic Tuning Range): Electronic Tuning Range for a particular mode is the total change in frequency from one end of the mode to the other. f max f min 3. ETS(Electronic Tuning Sensitivity): ETS = f 2 f1 vo 2 vo 1 Where f1 & f2 are half power (3db) frequencies and Vo2 and Vo1 are repeller voltages corresponding to 3db points. RESULTS: CONCLUSION: Dept. of E&C, Canara Engineering College, Mangalore. Page 24 Advanced Communication Lab Manual-10ECL67 Expt no-8a. STUDY OF PROPOGATION LOSS, IN OPTIACAL FIBER OBJECTIVE: The objective of this experiment is to measure propagation or attenuation loss in optical fiber. Block Diagram: THEORY: Attenuation is loss of power. During transit light pulse lose of their photons, thus reducing their amplitude. Attenuation for a fiber is usually specified in decibels per kilometer. For commercially available fibers attenuation ranges from 1dB/km for premium small-core glass fibers to over 2000dB/km for a large core plastic fiber. Loss is by definition negative decibels. In common usage, discussions of loss omit the negative sign. The basic measurement for loss in a fiber is made by taking the logarithmic ratio of the input power (Pi) to the output power (Po) (dB) 10 log 10 Pi Po Where is Loss in dB/Meter EXPERIMENTAL PROCEDURE: Connect power supply to board Make the following connections (as shown in block diagram) a) Function Generators 1Khz sinewave output to input 1 socket of emitter 1 circuit via 4mm lead. b) Connect 0.5 optic fiber between emitter 1 output and detector 1‟s input. c) Connect Detector 1 output to amplifier 1 input Socket via 4mm lead. Switch ON the power supply. Set the Oscilloscope channel 1 to 0.5V/Div and adjust 4-6 div amplitude by using X1 probe with the help of variable pot in function generator block at input 1 of Emitter 1. Observe the output signal from detector t p 28 on CRO. Adjust the amplitude of the received signal as that of transmitted one with the help of gain adjust pot in AC Amplifier block. Note this amplitude and name it V1. Now replace the previous F.O. cable with 1m cable without disturbing any previous setting. Dept. of E&C, Canara Engineering College, Mangalore. Page 25 Advanced Communication Lab Manual-10ECL67 1. Measure the amplitude at the receiver side again at output of amplifier 1 socket t p 28. Note this value end name it V2. Calculate the propagation (Attenuation) loss with the help of following formula. ( L1 L2) V1/V2 = e Where is loss in nepers/meter 1 neper = 8.686 dB ,L1 = Length of shorter cable (0.5m), L2 = Length of longer cable (1m) Dept. of E&C, Canara Engineering College, Mangalore. Page 26 Advanced Communication Lab Manual-10ECL67 8b. STUDY OF BENDING LOSS OBJECTIVE: The Objective of this experiment in to study of bending loss. THEORY: Whenever the condition for angle of incidence of the incident light is violated the losses are introduced due to refraction of light. This occurs when fiber is subjected to bending. Lower the radius of curvature more is the loss. EXPERIMENTAL PROCEDURE: 1. Repeat all the steps from 1 to 6 of the previous experiment No 7 using 1m cable. 2. Wind the FO cable on the mandrel and observe the corresponding AC amplifier output on CRO… it will be gradually reducing showing loss due to bends. TABULAR COLUMN: No of bends Output signal voltage in volts Without bending 1st bend 2nd bend 3rd bend Dept. of E&C, Canara Engineering College, Mangalore. Page 27 Advanced Communication Lab Manual-10ECL67 8c. MEASUREMENT OF NUMERICAL APERTURE OBJECTIVE: The Objective of this experiment is to measure to the Numerical Aperture (NA) of the Fiber. THEORY: Numerical aperture refers to the maximum angle at which the light incident on the fiber end is totally internally reflected and is transmitted properly along the fiber. The cone formed by the rotation of this angle along the axis of the fiber is the cone of acceptance of the fiber. The light ray should strike the fiber end within its cone of acceptance else it is refracted out of the fiber. Consideration in NA measurement: It is very important that the optical source should be properly aligned with the cable and the distance from the launched point & cable be properly selected to ensure that the maximum amount of optical power is transferred to the cable. Equipments: 1. Numerical Aperture measurement Jig. EXPERIMENTAL PROCEDURE: 1. Connect power supply to the board. 2. Connect the frequency generator‟s 1 KHz sine wave output to input of emitter 1 circuit. Adjust its amplitude at 5V p-p. 3. Connect one end of fiber cable to the output socket of emitter 1 circuit and the other end to the Numerical aperture measurement jig. Hold the white screen facing the fiber such that its cut face is perpendicular to the axis of the fiber. 4. Hold the white screen with 4 concentric circles (10, 15, 20 & 25mm diameter) vertically at a suitable distance to make the red spot from the fiber coincide with 10mm circle. Dept. of E&C, Canara Engineering College, Mangalore. Page 28 Advanced Communication Lab Manual-10ECL67 5. Record the distance of screen from the fiber end L and note the diameter W of the spot. 6. Compute the numerical aperture from the formula given below, N . A. W 4 L2 W 2 sin max 7. Vary the distance between in screen and fiber optic cable and make it coincide with one of the concentric circles. Note its distance. 8. Tabulate the various distances and diameter of the circles made on the white screen and compute the numerical aperture from the formula given above. TABULAR COLUMN: Distance of the Diameter W of the Numerical Aperture screen L in meters spot in meters (NA) RESULTS: CONCLUSION: Dept. of E&C, Canara Engineering College, Mangalore. Page 29 Advanced Communication Lab Manual-10ECL67 Expt No-9. MICROSTRIP DIRECTIONAL COUPLER AIM: To determine coupling and isolating characteristic of Microstrip Directional Coupler. COMPONENTS USED: Directional Couplers, VSWR meter, Microwave source. Directional Coupler Block Diagram: RF-OUT Microwave Source Diode Detector VSWR Meter Fig.1 RF-OUT Microwave Source Directional Coupler Diode Detector VSWR Meter Fig. 2 THEORY: Directional coupler is four port waveguide junction consisting of 2 primary waveguide (Port 1 & 2) and secondary waveguide (Ports 3 & 4). When all ports are terminated in either characteristic impedance, there is free transmission of power without reflection between port1 and port2 and there is no transmission of power between port1 and port3 or between 2 & 4. Because no coupling exists between these two pairs of ports. These are 3 directional coupler 3dB directional coupler, 10dB and 15dB branch line directional coupler. Dept. of E&C, Canara Engineering College, Mangalore. Page 30 Advanced Communication Lab Manual-10ECL67 Coupling Loss Amount of power lost to the coupled port (3) and to the isolated port (4). Assuming a reasonable directivity, the power transferred unintentionally to the isolated port will be negligible compared to that transferred intentionally to coupled port. Main line loss Resistive loss due to heating (separate from coupling loss). This value is added to the theoretical reduction in power that is transferred to the coupled and isolated ports (coupling loss). Directivity Power level difference between Port 3 and Port 4 (related to isolation). This is a measure of how independent the coupled and isolated ports are. Because it is impossible to build a perfect coupler, there will always be some amount of unintended coupling between all the signal paths. Isolation Power level difference between Port 1 and Port 4 (related to directivity). EXPERIMENTAL PROCEDURE: 1. 2. 3. 4. 5. 6. Experiment set up as shown in fig 1. Keep microwave source in internal AM mode. Note down output power from VSWR meter (vary the frequency from 2.1 GHz to 3GHz). Now experiment is setup as shown in figure 2. Keep microwave source in Internal AM mode. Apply RF signal to input port and note down coupling power in VSWR meter (vary the frequency from 2.1 GHz to 3GHz). 7. Terminate isolation port & direct port by 50 standard loads. 8. Repeat these steps to find the output power at direct port and isolating port. 9. Terminate unused ports by 50 . 10. Note down the all the readings and calculate coupling factor, Isolation factor, Insertion loss and directionality. Tabulation (Using VSWR meter ): Rf signal f (Ghz) Input Power at port 1(dB) P1 Transmitted power at port 2(dB) P2 coupled Power at port 3(dB) P3 Isolated power at port 4(dB) P4 Coupling Factor, Isolation Factor, Insertion Loss, C31(dB) = I41(dB) = L21(dB) P3-P1 P4-P1 =P2-P1 2.10GHz 2.15GHz . . . 3GHz RESULTS: CONCLUSION: Dept. of E&C, Canara Engineering College, Mangalore. Page 31 Directivity , D(dB) = I41 - C31 Advanced Communication Lab Manual-10ECL67 EXPT N0-10. MICROSTRIP RING RESONATOR AND POWER DIVIDER AIM: 1. To measure resonance characteristics of Microstrip Ring Resonator and determine dielectric constant of the substrate. 2. To measure power division and isolation characteristics of microstrip 3dB power divider. THEORY: The open-end effect encountered in a rectangular resonator of the feed long gaps can be minimized by forming the resonator as a closed off. Such resonator is called as Ring resonator. The Ring resonator find applications in the design of filters, oscillator and mixers. Resonance is established when the mean circumference of the ring is 2ro n equal to integral multiplies of guide wave length. nv o fo eff Where ro = radius of the ring, n = mode number, eff = effective dielectric constant of the substrate. Power Divider: The function of a power division network is to divide the input power into two or more outputs. As an equal split power divider, the power incident at port1 gets divided equally between the two output ports 2 & 3. Power at 2 & 3 is half power. i.e.-3dB down power. EXPERIMENTAL SET UP/BLOCKDIAGRAM: Microwave Source RF OUT Ring Resonator Diode Detector VSWR Meter Fig.1 CRO Dept. of E&C, Canara Engineering College, Mangalore. Page 32 Advanced Communication Lab Manual-10ECL67 EXPERIMENTAL PROCEDURE: 1. Experiment set up as shown in fig.1 2. Keep microwave generator in Internal AM mode. 3. Vary the RF out frequencies at 2.2GHz to 3GHz insteps of 0.1GHz and note down output detector power in VSWR meter. 4. Note down/ tabulate these results & note down the resonant frequency at which the output power is maximum. 5. Plot the graph output power Vs frequency. 6. Determine dielectric constant of the substrate of Ring Resonator. Power divider Characteristics: 1. Experiment set up as shown in fig.2 2. Apply RF power to input port and observe the half power at 2 output port. E.g. – If input power is -20dB, Output power is -23dB at each output port. Calculations: Dielectric constant of substrate r 2 eff 1 1 Where A 1 1 1 A A 10h area of W W = Stripline conductor width = 1.847mm h = Height of substrate = 0.762mm eff nvo 2r f o o 2 = Effective Dielectric constant n = 1, vo 3 108 m / s , ro 12.446mm radius of the ring f o Resonance frequency Dept. of E&C, Canara Engineering College, Mangalore. Page 33 Advanced Communication Lab Manual-10ECL67 EXPECTED GRAPH: Table Rf signal f (Ghz) Output power(Db) 2.1Ghz 3Ghz RESULTS CONCLUSION Dept. of E&C, Canara Engineering College, Mangalore. Page 34 Advanced Communication Lab Manual-10ECL67 EXPT N0-11. Study of Antenna Radiation Patterns (Simple, Folded Dipole) AIM: To determine Antenna Radiation pattern, Beam width and Front To back Ratio of Simple dipole and Folded dipole antennas. EXPERIMENTAL SET UP THEORY: Antennas can be broadly classified by the directions in which they radiate or receive electromagnetic radiation. They can be isotropic, omnidirectional or directional. An Isotropic antenna is a hypothetical antenna that radiates uniformly in all directions so that the electric field at any point on a sphere has the same magnitude. Such radiation cannot be realized in practice since in order to radiate uniformly in all directions an isotropic antenna would have to be a point source. A directional antenna radiates most of its power in one particular direction examples of directional antennas are Yagi UDA, log-Periodic and helical. EXPERIMENTAL PROCEDURE Experiment A 1) Arrange the setup as shown in figure. 2) Mount simple dipole (λ/2) on the transmission mask. 3) Bring the detector assembling near to main unit and adjust height of both transmitting and receiving antenna same. 4) Keep detector away from main unit approximately 1.5 meter and align both of them. 5) Keep the RF level and FS adjust to minimum level and directional coupler switch to FWD. 6) Keep detector level control in the center approximately. 7) Increase the RF level gradually and see there is a deflection the detector meter. Dept. of E&C, Canara Engineering College, Mangalore. Page 35 Advanced Communication Lab Manual-10ECL67 8) Adjust RF level and detector level so that deflection in detector meter is approximately 30-35μA. 9) Align arrow mark on the disk with zero of the gonio meter scale. 10) Start taking the reading at the interval of 5 or 10degre. 11) Convert micro ampere reading into dB, with the help of conversion chart. 12) Plot the polar graph in degrees of rotation of antenna against level in the detector in dBs. 13) From the graph calculate: a) beam width b) front/back ratio c) Gain of antenna 14) To calculate these from the graph proceed as follows. Beam width: 1. Look for main lobe 2. Draw bore sight maxima line AA‟ 3. Mark -3dB from maximum on the bore sight line point B 4. Draw an arc of radius AB 5. This arc will intersect main lobe at CD 6. Measure angle CAD. This angle is -3Db beam width. Front to Back Ratio 1. Look for main lobe 2. Draw bore sight maxima line AA‟ 3. Look for back lobe if any (at 180deg) 4. If no back lobe then front to back ratio =AA‟/1 dB 5. If there is back lobe then measure AE, where E is the maxima of back lobe then 6. front to back ratio = AA‟/AE dB GAIN OF ANTENNA = Maximum radiation intensity = AA‟/1 dB Experiment B Replace λ/2 antenna with λ/4 antenna and follow the steps given in Experiment A. TABLE ANGLE IN DEGREES 0 20 40 . . . 360. GAIN IN dB Dept. of E&C, Canara Engineering College, Mangalore. Page 36 Advanced Communication Lab Manual-10ECL67 Simple dipole radiation Pattern Folded Dipole radiation Pattern RESULTS CONCLUSION Dept. of E&C, Canara Engineering College, Mangalore. Page 37 Advanced Communication Lab Manual-10ECL67 EXPT N0-12. Measurement of directivity and gain of antennas: Standard dipole (or printed dipole), microstrip patch antenna and Yagi antenna (printed). Aim: To find the directivity and gain of Antennas. Apparatus required: 1. Microwave Generator 2. SWR Meter 3. Detector 4. RF Amplifier 5. Transmitter and receiving mast 6. Mains cord 7. Antennas o Yagi Antenna (Dielectric Constant: 4.7) - 2 no. o Dipole Antenna (Dielectric Constant: 4.7) - 1 no. o Patch Antenna (Dielectric Constant: 3.02) - 1 no. Theory: If a transmission line propagating energy is left open at one end, there will be radiation from this end. The Radiation pattern of an antenna is a diagram of field strength or more often the power intensity as a function of the aspect angle at a constant distance from the radiating antenna. An antenna pattern is of course three dimensional but for practical reasons it is normally presented as a two dimensional pattern in one or several planes. An antenna pattern consists of several lobes, the main lobe, side lobes and the back lobe. The major power is concentrated in the main lobe and it is required to keep the power in the side lobes arid back lobe as low as possible. The power intensity at the maximum of the main lobe compared to the power intensity achieved from an imaginary omni-directional antenna (radiating equally in all directions) with the same power fed to the antenna is defined as gain of the antenna. As we know that the 3dB beamwidth is the angle between the two points on a main lobe where the power intensity is half the maximum power intensity. When measuring an antenna pattern, it is normally most interesting to plot the pattern far from the antenna. It is also very important to avoid disturbing reflection. Antenna measurements are normally made at anechoic chambers made of absorbing materials. Antenna measurements are mostly made with unknown antenna as receiver. There are several methods to measure the gain of antenna. One method is to compare the unknown antenna with a standard gain antenna Dept. of E&C, Canara Engineering College, Mangalore. Page 38 Advanced Communication Lab Manual-10ECL67 with known gain. Another method is to use two identical antennas, as transmitter and other as receiver. From following formula the gain can be calculated. Where, Pt is transmitted power Pr is received Power, G1, G2 is gain of transmitting and receiving antenna S is the radial distance between two antennas o is free space wave length. If both, transmitting and receiving antenna are identical having gain G then above equation becomes. In the above equation Pt, Pr and S and o can be measured and gain can be computed. As is evident from the above equation, it is not necessary to know the absolute value of Pt and Pr only ratio is required which can be measured by SWR meter. Setup for Directivity measurement Dept. of E&C, Canara Engineering College, Mangalore. Page 39 Advanced Communication Lab Manual-10ECL67 Procedure: Directivity Measurement: 1. Connect a mains cord to the Microwave Generator and SWR Meter. 2. Now connect a Yagi antenna in horizontal plane to the transmitter mast and connect it to the RF Output of microwave generator using a cable (SMA to SMA). 3. Set both the potentiometer (Mod Freq & RF Level) at fully clockwise position. 4. Now take another Yagi antenna and RF Amplifier from the given suitcase. 5. Connect the input terminal of the Amplifier to the antenna in horizontal plane using an SMA (male) to SMA (female) L Connector. 6. Now connect the output of the Amplifier to the input of Detector and mount the detector at the Receiving mast. 7. Connect one end of the cable (BNC to BNC) to the bottom side of receiving mast, and another end to the input of SWR meter. 8. Now set the distance between Transmitter (feed point) and the receiver (receiving point) at half meter. Antenna Under Test RF Amplifier Detector Yagi Antenna SWR Meter Receiver Microwave Generator Transmitter Dept. of E&C, Canara Engineering College, Mangalore. Page 40 Advanced Communication Lab Manual-10ECL67 9. Now set the receiving antenna at zero degree (in line of Transmitter) and Switch on the power supply for Microwave Generator, SWR Meter. Also connect DC Adapter of RF Amplifier to the mains. 10. Select the transmitter for internal AM mode and press the switch “RF On”. 11. Select the range switch at SWR meter at – 40dB position with normal mode. 12. Set both the gain potentiometers (Coarse & Fine) at fully clockwise position and input select switch should be at 200 Ohm position. In case if reading is not available at – 40dB range then press 200 kOhm (Input Select) to get high gains reading. 13. Now set any value of received gain at – 40dB position with the help of o Frequency of the Microwave Generator. o Modulation frequency adjustment. o Adjusting the distance between Transmitter and Receiver. 14. With these adjustments you can increase or decrease the gain. 15. Mark the obtained reading on the radiation pattern plot at zero degree position. 16. Now slowly move the receiver antenna in the steps of 10 degree and plot the corresponding readings. 17. This will give the radiation pattern of the antenna under test. 18. Directivity of the antenna is the measures of power density an actual antenna radiates in the direction of its strongest emission, so if the maximum power of antenna (in dB) is received at degree then directivity will be ....................dB at ........................Degree. 19. In the same way you can measure the directivity of the Dipole antenna. 20. For directivity measurement of the transformer fed Patch antenna connect transmitter Yagi antenna in the vertical plane (Patch Antenna is vertically polarized). Since it is comparatively low gain antenna distance can be reduced between transmitter and receiver. Gain Measurement: 1. Connect a power cable to the Microwave Generator and SWR Meter. 2. Now connect a Yagi antenna in horizontal plane to the transmitter mast and connect it to the RF Output of microwave generator using a cable (SMA to SMA). 3. Set both the potentiometer (Mod Freq & RF Level) at fully clockwise position. 4. Now take another Yagi antenna from the given suitcase. 5. Connect this antenna to the detector with the help of SMA (male) to SMA (female) L Connector. 6. Connect detector to the receiving mast. 7. Connect one end of the cable (BNC to BNC) to the bottom side of receiving mast, and another end to the input of SWR meter. Dept. of E&C, Canara Engineering College, Mangalore. Page 41 Advanced Communication Lab Manual-10ECL67 8. Now set the distance between Transmitter (feed point) and the receiver (receiving point) at half meter. 9. Now set the receiving antenna at zero degree (in line of Transmitter) and Switch on the power from both Generator & SWR Meter. 10. Select the transmitter for internal AM mode and press the switch “RF On”. 11. Select the range switch at SWR meter at – 40dB position with normal mode. 12. Set both the gain potentiometers (Coarse & Fine) at fully clockwise position and input select switch should be at 200 Ohm position. In case if reading is not available at – 40dB range then press 200 kOhm (Input Select) to gets high gain reading. 13. Now set the maximum gain in the meter with the help of following o Frequency of the Microwave Generator. o Modulation frequency adjustment. o Adjusting the distance between Transmitter and Receiver. 14. Measure and record the received power in dB. Pr = ..................dB 15. Now remove the detector from the receiving end and also remove the transmitting Yagi antenna from RF output. 16. Now connect the RF output directly to detector without disturbing any setting of the transmitter (SMA-F to SMA-F connector can be used for this). 17. Observe the output of detector on SWR meter that will be the transmitting power Pt. Pt = ..................dB 18. Calculate the difference in dB between the power measured in step 14 and 17 which will be the power ratio Pt/Pr . Pt/Pr = ........................ Pr/Pt = ........................ 19. Now we know that the formula for Gain of the antenna is: Dept. of E&C, Canara Engineering College, Mangalore. Page 42 Advanced Communication Lab Manual-10ECL67 Where: Pt is transmitted power Pr is received Power, G is gain of transmitting/receiving antenna (since we have used two identical antennas) S is the radial distance between two antennas o is free space wave length (approximately 12.5cm). 20. Now put the measured values in the above formula and measure the gain of the antenna which will be same for both the antennas. Now after this step you can connect one known gain antenna at transmitter end and the antenna under test at receiver end, to measure the gain of the antennas. 21. Gain can be measured with the help of absolute power meter also (Recommended Model NV105). for this detector will not be used and directly the power sensor can be connected to both the ends as described earlier. Radiation Patterns of Different Antennas: 11 0 12 1 00 90 80 1 00 110 70 12 60 0 80 70 60 50 0 13 50 14 4 1 40 40 0 0 13 90 0 15 0 16 0 1 70 1 70 180 -44 -48 190 180 34 0 33 0 0 21 0 33 21 0 340 0 20 19 0 -52 3 50 35 0 0 20 -56 0 -60 0 -44 -48 10 10 -52 20 20 1 60 15 30 -56 30 0 0 -60 0 22 0 0 0 22 32 32 0 31 23 30 290 0 0 31 2 40 0 28 0 27 0 26 0 23 30 250 0 240 0 290 Patch Antenna 28 0 27 0 26 0 2 50 Yagi Antenna 110 12 10 0 90 80 70 0 60 50 10 17 0 20 16 0 15 30 0 14 40 0 0 13 1 80 -56 -52 -48 -44 0 -60 1 90 3 50 0 20 34 0 0 21 0 33 0 0 22 32 0 31 23 30 290 0 2 40 0 28 0 27 0 26 0 250 Dipole Antenna Dept. of E&C, Canara Engineering College, Mangalore. Page 43 Advanced Communication Lab Manual-10ECL67 TABLE ANGLE IN DEGREES 0 20 40 . . . 360 GAIN IN dB RESULTS CONCLUSION Dept. of E&C, Canara Engineering College, Mangalore. Page 44 Advanced Communication Lab Manual-10ECL67 EXPT N0-13. A) Analog Communication Link using Optic Fiber Objective: To Study the relationship between the input signal and received signal in a 650 nm Fiber Optic Analog Link. Equipments Required: 1. ST2501 Trainer with power supply cord 2. Optical Fiber cable 3. Cathode ray oscilloscope with necessary connecting probe Connection Diagram: Theory: In fiber optic communication systems, lasers are used to transmit messages in numeric code by flashing on and off at high speeds. This code can constitute a voice or an electronic file containing, text, numbers, or illustrations, all by using fiber optics. The light from many lasers are added together onto a single fiber optic enabling thousands of currents of data to pass through a single fiber optic cable at one time. This data will travel through the fiber optics and into interpreting devices to convert the messages back into the form of its original signals. Industries also use fiber optics to measure temperatures, pressure, acceleration and voltage, among an assortment of other uses. Procedure: Dept. of E&C, Canara Engineering College, Mangalore. Page 45 Advanced Communication Lab Manual-10ECL67 1. Connect the power supply cord to the main power plug & to trainer ST2501. 2. Ensure that all switched faults are OFF. 3. Make the connections as shown in above figure. a. Connect the function generator 1 KHz sine wave output to emitter input. b. Connect the fiber optic cable between emitter output and detector input. c. Connect the detector output to AC amplifier input. 4. On the board, put switch SW1 emitter driver to Analog mode. 5. Switch „On‟ the power supply of the trainer and oscilloscope. 6. Observe the input to emitter (TP5) with the output from AC amplifier (TP19) on CRO. Observation: Both the input and output waveforms are same. Input signal voltage Output signal frequency voltage frequency Conclusion: Dept. of E&C, Canara Engineering College, Mangalore. Page 46 Advanced Communication Lab Manual-10ECL67 EXPT N0-13. B) Digital Communication Link using Optic Fiber Objective: To Study the relationship between the input signal and received signal in a 650 nm Fiber Optic Digital Link. Equipments Required: 1. ST2501 Trainer with power supply cord 2. Optical Fiber cable 3. Cathode ray oscilloscope with necessary connecting probe Connection Diagram: Theory: In fiber optic communication systems, lasers are used to transmit messages in numeric code by flashing on and off at high speeds. This code can constitute a voice or an electronic file containing, text, numbers, or illustrations, all by using fiber optics. The light from many lasers are added together onto a single fiber optic enabling thousands of currents of data to pass through a single fiber optic cable at one time. This data will travel through the fiber optics and into interpreting devices to convert the messages back into the form of its original signals. Industries also use fiber optics to measure temperatures, pressure, acceleration and voltage, among an assortment of other uses. Procedure: Dept. of E&C, Canara Engineering College, Mangalore. Page 47 Advanced Communication Lab Manual-10ECL67 1. Connect the power supply cord to the main power plug & to trainer ST2501. 2. Ensure that all switched faults are OFF. 3. Make the connections as shown in above figure. a. Connect the function generator 1 KHz square wave output to emitter input b. Connect the fiber optic cable between emitter output and detector input. c. Connect the detector output to comparator input. d. Connect the comparator output to AC amplifier input 4. On the board, put switch SW1 in emitter circuit to digital mode. 5. Switch „On‟ the power supply of trainer and oscilloscope. 6. Monitor both the inputs to comparator (TP9 & 10). Slowly adjust the comparator bias preset, until DC level on the input (TP9) lies mid-way between the high and low level of the signal on the positive input (TP11) Observations: Observe the input to emitter (TP5) with the output from AC amplifier (TP19) and note that the two signals are the same. Input signal voltage Output signal frequency voltage frequency Conclusion: Dept. of E&C, Canara Engineering College, Mangalore. Page 48 Advanced Communication Lab Manual-10ECL67 EXPT N0-14. PCM Generation and Detection using CODEC Chip Objective: Study of PCM Generation and Demodulation of analog signal Equipments Required: 1. ST2123 PCM Generation & Demodulation using CODEC Chip 2. 2 mm Patch chords 3. Oscilloscope Caddo 803 or equivalent with connecting cable Theory: Pulse Code Modulation (PCM) is an extension of PAM wherein each analog sample value is quantized into a discrete value for representation as a digital code word. Thus, as shown below, a PAM system can be converted into a PCM system by adding a suitable analogue-to-digital (A/D) converter at the source and a digital-to-analogue (D/A) converter at the destination. PCM is a true digital process as compared to PAM. In PCM the speech signal is converted from analogue to digital form. In Pulse Modulation, analog message is transmitted in discrete time. First of all, sampling of the message signal should be performed. Considering the sampling process, the sampled signal appears as a train of samples which is a form of PAM (Pulse Amplitude Modulation) signal. When M levels are used to quantize this signal, this modulation is called M-PAM. If those pulses were converted to digital numbers, then the train of numbers so generated would be called as Pulse Code Modulated. PCM signal. In PCM, modulation process is executed in three steps: 1. Sampling 2. Quantizing 3. Coding These steps are shown below with a block diagram: Dept. of E&C, Canara Engineering College, Mangalore. Page 49 Advanced Communication Lab Manual-10ECL67 PCM block Diagram PCM Coding of Analog or Voice Signals Dept. of E&C, Canara Engineering College, Mangalore. Page 50 Advanced Communication Lab Manual-10ECL67 Connection diagram: Procedure: 1. Connect the power supply mains cord to the ST2123 but do not turn ON the power supply until connections are made for this experiment. 2. Make the following connections as shown in figure above. 3. From Clock Source, connect 1.5MHz Clock output to System Clock of Sample Rate Generator. 4. Switch „On‟ the power supply of trainer and oscilloscope. 5. Connect Channel CLK to LRCIN and Bit CLK to BCKIN 6. Observe the signal available on Channel CLK and Bit CLK on oscilloscope with respect to ground terminal provided on board. 7. Connect the Output of AC Source to VIN of ST2123 as shown in connection diagram in order to provide analog signal for modulation. 8. Observe the signal of DOUT on oscilloscope with respect to ground, which shows the modulated signal. 9. Connect the signal DOUT of ADC to DIN of DAC for demodulation of signal presented at input terminal 10. Observe the demodulated signal waveform at oscilloscope by connecting VOUT terminal of DAC to oscilloscope with respect to ground of board. 11. Change the System Clock of Sample Rate Generator to 3MHz, 6MHz and 12MHz; observe the effect of respective changes on PCM coding decoding. Dept. of E&C, Canara Engineering College, Mangalore. Page 51 Advanced Communication Lab Manual-10ECL67 Observations: System Clock Input Analog Signal Vin(P-P) Frequency Generated PCM signal Dout(P-P) Frequency Detected Analog Signal Vout (P-P) Frequency 1.5 MHz 3 MHz 6 MHz 12 MHz · Signals available on output (Vout), after PCM coding followed by decoding is same as analog signal given at input of codec. · PCM Coding is method of converting analog signal to digital signal that‟s why the output of ADC Dout in this codec is digital levels showing the instantaneous changes of analog signal. · Channel CLK and bit CLK vary with change in system clock. Conclusion: 1. The PCM codec is an analog-digital interface for voice band signals designed with a combination of coders and decoders (codecs) and filters. 2. It is a low-power device with companding options, and it meets the requirements for communication systems, including the cellular phone. The device operates in either the 15-bit linear or 8-bit companded. 3. Channel CLK and bit CLK is highest for 12MHz system clock Dept. of E&C, Canara Engineering College, Mangalore. Page 52 Advanced Communication Lab Manual-10ECL67 Bibliography 1. Digital communications, Simon Haykin, John Wiley India Pvt. Ltd, 2008. 2. Digital and Analog communication systems, Simon Haykin, John Wildy India Lts, 2008 3. An introduction to Analog and Digital Communication, K. Sam Shanmugam, John Wiley India Pvt. Ltd, 2008. 4. Digital communications - Bernard Sklar: Pearson education 2007 5. Microwave Devices and circuits- Liao / Pearson Education. 6. Microwave Engineering – Annapurna Das, Sisir K Das TMH Publication, 2nd , 2010. 7. Microwave Engineering – David M Pozar, John Wiley India Pvt. Ltd., 3rd Edn, 2008. 8. Antennas and Wave Propagation, John D. Krauss, 4th Edn,McGraw-Hill International edition, 2010. 9. Antennas and Wave Propagation - Harish and Sachidananda: Oxford Press 2007 10. Antenna Theory Analysis and Design - C A Balanis, 3rd Edn, John Wiley India Pvt. Ltd, 2008 11. Antennas and Propagation for Wireless Communication Systems - Sineon R Saunders, John Wiley, 2003. 12. Antennas and wave propagation - G S N Raju: Pearson Education 2005 13. Optical Fiber Communication, Gerd Keiser, 4th Ed., MGH, 2008. 14. Optical Fiber Communications John M. Senior, Pearson Education. 3rd Impression, 2007. Dept. of E&C, Canara Engineering College, Mangalore. Page 53 Advanced Communication Lab Manual-10ECL67 VIVA QUESTIONS FOR ADVANCED COMMUNICATION LAB 1. State different types of Digital modulation techniques? 2. What is shift keying? 3. What is a binary modulation technique? 4. Define ASK? 5. Define FSK? 6. Define PSK? 7. Define QPSK and DPSK? 8. Why QPSK is called quadrature shift keying? 9. Define TDMA? 10. What are applications of shift keying? 11. Define FDM? 12. State the applications of multiplexing? 13. State the principle of PLL? 14. State coherent detection? 15. State non-coherent detection? 16. Differentiate between DPSK and QPSK? 17. What is an M-Array data transmission? 18. What is a standing wave? 19. Define reflection and transmission co-efficient? 20. State different types of losses in transmission lines? 21. Define modes? 22. What is the range of microwaves? 23. What is the advantage of waveguides? 24. Define VSWR? Dept. of E&C, Canara Engineering College, Mangalore. Page 54 Advanced Communication Lab Manual-10ECL67 25. Define Isolator? 26. What is the principle of Directional coupler? 27. State different types of Directional couplers? 28. What is a Klystron? 29. State the classification of microwave tubes? 30. What are O-type and M-type tubes? 31. State application of klystron? 32. State the mechanism of oscillation in klystron? 33. How modulation occurs in reflex klystron? 34. State two methods to find VSWR? 35. Define the principle of slotted line carriage? 36. Differentiate between normal and expanded SWR? 37. What type of frequency meter is used in Laboratory? 38. Define directivity, radiation efficiency, beam width and bandwidth of an antenna? 39. What are the radiation patterns for Horn antenna, parabolic antenna? 40. State the formula to find directivity for an antenna? 41. What are the advantages of using optical fibers? 42. What is the principle of operation of OFC? 43. State the difference between step-index and graded index fiber? 44. State the formula to find the numerical Aperture? 45. What are the different types of losses in OFCS? Dept. of E&C, Canara Engineering College, Mangalore. Page 55
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