INDEX. 6 Measurement of radiation pattern of a loop antenna in principal planes.

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1 INDEX S.No Date NAME OF THE EXPERIMENT Marks Sign 1 Amplitude modulation & demodulation 2 Frequency modulation & demodulation 3 Pulse Amplitude modulation & demodulation 4 Radio Receiver measurements-sensitivity, Selectivity & Fidelity 5 Measurement of half power beam width (HPBW) and gain of a half wave dipole antenna. 6 Measurement of radiation pattern of a loop antenna in principal planes. 7 Time division multiplexing 8 Pulse code modulation 9 Delta modulation 10 Frequency shift keying 11 QPSK modulation & demodulation 12 Differential phase shift keying 13 Time division multiplexing using MAT LAB 14 Pulse code modulation using MAT LAB 15 Delta modulation using MAT LAB 16 Frequency shift keying using MAT LAB 17 QPSK modulation & demodulation using MAT LAB 18 Differential phase shift keying using MAT LAB

2 ANALOG & DIGITAL COMMNICATIONS LAB 1. AMPLITUDE MODULATION & DEMODULATION Aim: 1. To generate amplitude modulated wave and determine the percentage modulation. 2. To Demodulate the modulated wave using envelope detector Apparatus: 1. Amplitude Modulation & Demodulation trainer Kit 2. Dual trace oscilloscope 3. Patch cords. Theory: Amplitude Modulation is a process in which the amplitude of the carrier wave c(t) is varied linearly with the instantaneous amplitude of the message signal m(t).the standard Form of amplitude modulated (AM) wave is defined by s(t)= Ac(1+ Ka m(t) cos 2πfct) Where Ka is a constant called the amplitude sensitivity of the modulator. The demodulation circuit is used to recover the message signal from the incoming AM wave at the receiver. An envelope detector is a simple and yet highly effective device that is well suited for the demodulation of AM wave, for which the percentage modulation is less than 100%.Ideally, an envelope detector produces an output signal that follows the envelop of the input signal wave form exactly; hence, the name. Some version of this circuit is used in almost all commercial AM radio receivers. The Modulation Index is defined as, m=. Where Emax and Emin are the maximum and minimum amplitudes of the modulated wave. SIETK Page 2

3 ANALOG & DIGITAL COMMNICATIONS LAB Circuit Diagrams: Modulation SIETK Page 3

4 ANALOG & DIGITAL COMMNICATIONS LAB Demodulation: SIETK Page 4

5 ANALOG & DIGITAL COMMNICATIONS LAB Procedure: 1. As the circuitry is already wired you just have to trace the circuit according to the circuit diagram given 2. Connect trainer to the mains and switch ON the power supply 3. Measure the output voltages of regulated power supply circuit that is,+12v and -12v. 4. Observe output of RF and AF signal generator using CRO.Note that RF voltage is approximately 300mv pp of 1 MHZ frequency and AF voltage is 10 v pp of 2 KHZ frequency. Modulator 1. Now connect RF and AF signals to the respective inputs of modulator. 2. Initially set both the signals at Zero level. 3. Connect one of the input of oscilloscope to modulator output and other input to AF signal 4. Adjust RF signal amplitude with the help of potentiometer so that output of the modulator is nil pp by keeping AF signal at zero level 5. Now vary the amplitude of AF signal and observe the amplitude modulated wave at output. Note the percentage of modulation for different values of AF signal. Percentage of modulation can be calculated by below formula % modulation = Demodulator: 1. Now connect the modulator output to the demodulator input 2. Observe demodulated signal at output of modulator at approximately 50 % modulation using oscilloscope 3. Compare it with the original AF signal.( Note only wave shape,amplitude will be attenuated,phase may change) 4. Find the detected signal is same as the AF signal applied.thus no information is lost in the process of modulation. SIETK Page 5

6 ANALOG & DIGITAL COMMNICATIONS LAB If you want to observe AM wave at different frequencies then connect AF signal from external signal generator to the modulator and observe amplitude modulated wave at different frequencies. Waveforms: Result: Viva -Voice 1. Define AM and draw its spectrum? 2. Give the significance of modulation index? 3. What are the different degrees of modulation? 4. What are the limitations of square law modulator? 5. Compare linear and nonlinear modulators? SIETK Page 6

7 ANALOG & DIGITAL COMMNICATIONS LAB 2. FREQUENCY MODULATION AND DEMODULATION Aim: 1. To generate frequency modulated signal and determine the modulation index and bandwidth for various values of amplitude and frequency of modulating signal. 2. To demodulate a Frequency Modulated signal using FM detector. Apparatus: 1. Frequency Modulation & Demodulation ACLT002 trainer kit 2. Dual trace oscilloscope 3. Patch cords Theory: The process, in which the frequency of the carrier is varied in accordance with the instantaneous amplitude of the modulating signal is called Frequency Modulation. The FM signal is expressed as S (t) =A c sin (2πf c t+β Sin (2πf m t) Where Ac is amplitude of the carrier signal, f c is the carrier frequency,β is the modulation index of the FM wave. SIETK Page 7

8 ANALOG & DIGITAL COMMNICATIONS LAB Circuit Diagrams: Modulation SIETK Page 8

9 ANALOG & DIGITAL COMMNICATIONS LAB Demodulation: SIETK Page 9

10 ANALOG & DIGITAL COMMNICATIONS LAB Procedure: 1. As the circuitry is already wired you just have to trace the circuit according to the circuit diagram given 2. Connect trainer to the mains and switch ON the power supply 3. Measure the output voltages of regulated power supply circuit that is,+15v and -15v, +5v and -5v 4. Observe output of AF signal generator using CRO.Note that AF voltage is approximately 20v pp of 500KHZ & 5KHZ frequency.(switch is provided to change the frequency ) Modulation: 1. Connect the patch cord SO1 AF output to Modulating signal input SO2. 2. Connect ground to ground SG1 to SG2. 3. Vary the modulation POT 4. Observe the FM output on SO4 or TP4 Demodulation: 1. Connect the patch cords from SO4 to SO5 2. Connect the patch cords from GND to GND 3. Observe the Demodulation output at SO6 or TP6 Tabular columns: Modulating signal Modulated signal Demodulated signal Amplitude Time period frequency SIETK Page 10

11 ANALOG & DIGITAL COMMNICATIONS LAB Waveforms: Result: Viva Voice: 1. Define FM & PM. 2. What are the advantages of Angle modulation over amplitude modulation? 3. What is the relationship between PM and FM? 4. With a neat block diagram explain how PM is generated using FM. 5. What is broadcasting range of FM SIETK Page 11

12 ANALOG & DIGITAL COMMNICATIONS LAB 3. PULSE AMPLITUDE MODULATION & DEMODULATION Aim: To generate the Pulse Amplitude modulated and demodulated signals. pparatus: 1. Pulse amplitude Modulation & Demodulation trainer kit 2. Dual trace Oscilloscope 3. Patch cords Theory: In Flat top sampling, the amplitude of the samples remain constant at an instant of time unlike in natural sampling where the amplitude of the samples vary in accordance with the amplitude of the input signal that is to be sampled. The generation of flat top samples involves two stages as shown in the figure given below. Analog Sample & Hold S/H o/p Switch Signal Flat-top Samples Single polarity Flat-top samples For generating the flat top samples, the signal to be sampled is first fed to a Sample and hold amplifier which generates the staircase waveform as represented in the above graph at the point D. The sampling clock selected determines the hold period of the S/H waveform. The resulting waveform is then passed on to a electronic switch (sampler), which latches the samples of the S/H waveform for the period determined by the duty cycle of the input sampling clock. The resulting samples are flat-topped corresponding to the flat portions of the input S/H wave. SIETK Page 12

13 ANALOG & DIGITAL COMMNICATIONS LAB Circuit Diagram: Modulation Switch to Natural PAM Modulator 1 KHz A1 A2 C E1 4 KHz PAM 8 KHz C Demodulation: PAM Modulator Amplifier Demodulator E1 E B1 B2 LPF Fc =3.4KHz B2 B F1 Phase Adjust SIETK Page 13

14 ANALOG & DIGITAL COMMNICATIONS LAB Procedure: Modulation 1. Connect signal source 1 KHz (A1) to (A) as shown in the interconnection diagram with the help of the patch cords given. 2. Select sampling frequency to 8 KHz 3. Select natural sampling by pushing the switch to the extreme left as shown in the figure 4. Adjust pulse width potentiometer to extreme anti clockwise 5. Connect the oscilloscope with the input analog signal A1 and with the PAM modulator output E1. Observations: 1. The PAM modulator output will be a product of input analog signal and regularly spaced pulse train. 2. Note the pulse width of PAM and by varying the pulse width potentiometer, record the pulse width of PAM 3. Determine the minimum and maximum duty cycle of pulse 4. Determine the minimum and maximum duty cycle of pulse at 4 KHz, 16 KHz and 32 KHz. 5. Repeat the above experiment by connecting 2 KHz (A2) to (A) Demodulation 1. Connect the signal source 1 KHz (A1) to (A), PAM output (E1) to receiver input (E) and PAM demodulator output (B2) to LPF input (B). 2. Select sampling frequency to 8 KHz 3. Select flat sampling 4. Connect the oscilloscope with the signal B1 and sampling pulse regenerator output G. Observations: 1. Observe the relative position of PAM pulses and sampling pulses. 2. Record the PAM demodulator output at B2. 3. Vary the phase adjust potentiometer gradually till the sampling pulses are in middle of PAM pulses 4. Record the PAM demodulator output at B2, which will be a step signal. 5. Observe the reconstructed output at F1. 6. Vary the pulse width of PAM pulses and observe the reconstructed output at F1 7. Repeat the above procedure at other sampling frequencies 8. Explain the distortion if the sampling frequency is 4 KHz. N O TE: For phase adjust at 16 & 32 KHz vary the potentiometer VR11 SIETK Page 14

15 ANALOG & DIGITAL COMMNICATIONS LAB Modulated Wave forms: Demodulation Waveforms SIETK Page 15

16 ANALOG & DIGITAL COMMNICATIONS LAB Result: Viva Voice: 1. Explain the modulation circuit operation? 2. Explain the demodulation circuit operation? 3. Is PAM & Demodulation is sensitive to Noise? 4. What is cross talk in the context of time division multiplexing? 5. Which is better, natural sampling or flat topped sampling and why? SIETK Page 16

17 ANALOG & DIGITAL COMMNICATIONS LAB 4. Radio receiver measurements sensitivity selectivity and Ffidelity AIM: To transmit a modulating signal after frequency modulation using VCT-12 and receive the signal back after demodulating using VCT-13 APPARATUS REQUIRED: 1. VCT-12 trainer kit 2. VCT-13 trainer kit 3. CRO 4. Patch cards HARDWARE DESCRIPTION OF FM TRANSMITTER TRAINER VCT-12: The FM transmitter trainer kit VCT-12 has the following section: 1. On-board sine wave generator 2. MIC pre amplifier with a socket for external dynamic MIC 3. Audio amplifier for amplification of low level external input signal 4. Frequency modulation 5. Telescopic whip antenna SINE WAVE GENERATOR: A sine wave generator acts as an on board modulating signal source and generates an audio frequency sine wave.the amplitude of this sine wave generator varies from 0-5 V. However the output voltage from this source is controlled using a Trim pot to get an output signal in the range of 0-3V.The frequency of the signal varies from 300Hz to 15KHz.Since the amplitude of the source is large enough to modulate the carrier it need not be amplified,instead it can be directly connected to the input of the amplitude modulator. MIC PRE AMPLIFIER: The MIC pre amplifier is capable of accurately amplifying even a very low level signal, picked up by the MIC to the required level to modulate the carrier. This section has a EP socket at its input stage where, in an external dynamic MIC can be plugged in the gain of the stage can be controlled by the user by adjusting the potentiometer Pot4.The maximum gain of this stage can be achieved in this is 200.The maximum level of the input signal to this amplifier, so as to produce an amplified output without saturation is 60mV. AUDIO AMPLIFIER: The audio amplifier stage has a BJT common emitter configuration. This audio amplifier can be used to amplify any lower level external modulating signal whose voltage level is below 100mV.The gain of this stage can also be controlled by the user by varying the pot meter POT- 5.The maximum gain of this audio amplifier is 10. SIETK Page 17

18 ANALOG & DIGITAL COMMNICATIONS LAB FREQUENCY MODULATION: The frequency modulator circuit is constructed around a BF495, high frequency small signal BJT. The collector circuit of the transistor consists of a tank circuit formed by a inductor and capacitor. This tank circuit together with the transistor acts as an oscillator and produces the carrier frequency.the transistor circuit appears to the oscillator as a variable capacitance. This capacitance adds to the capacitance of the oscillator-tuned circuit. The size of this capacitance depends on the change in the collector current which occurs for a given change in base voltage and this is determined by the Trans conductance of the transistor.the transistor trans conductance depends on the bias voltage applied to the transistor base. The larger the bias voltage, the larger the value of gm and the larger the value of gm and the larger capacitance which is added to the capacitance of the oscillator tuned circuit consequently the transistor circuit behaves as a voltage variable capacitance.the bias voltage applied to the transistor base determines the overall capacitance seen by the oscillator and hence the frequency of the carrier. This resulting in FM signal TELSCOPIC WHIP ANTENNA: A telescopic whip antenna is used to radiate the AM signal generated by the amplitude modulator. HARDWARE DESCRIPTION OF FM RECEVIER TRAINER The FM receiver trainer VCT-13 has the following sections 1. FM super heterodyne receiver 2. Buffer and filter 3. Audio power amplifier FM SUPER HETERODYNE RECEIVER: The FM receiver is built with the dedicated FM receiver IC-CXA1619IC consists of the following sections namely RF amplifier,mixer and oscillator, IF amplifier and quadrature detector.the circuit details and the description of IC-CXA1619IC are given in appendix BUFFER AND FILTER: A buffer is used to prevent any loading to the previous stage.the filter section consists of a BPF with a Pass band to 20KHZ 15MHZ.A notch filter is also included to eliminate the 50Hz power supply noise SIETK Page 18

19 ANALOG & DIGITAL COMMNICATIONS LAB AUDIO POWER AMPLIFIER: The Audio power amplifier is constructed using ICTBA810 to increase the power level of the demodulated message signal to the required level. The gain of this amplifier can be adjusted by the user by varying the pot meter POT-1.the maximum gain of this audio amplifier is 25. The amplified signal can be given to a loud signal which can be extremely plugged into the VCT-13 trainer FM Transmitter: Audio Oscillator Message signal Antenna FM Modulator Output Amplifier Carrier generator FM Receiver: RF Amplifier Mixer IF amplifier Local Oscillator Discriminator AF Amplifier PROCEDURE: 1. The circuit wiring is done as shown in diagram 2. A modulating signal input given to the Frequency modulator can also be given From a external function generator or an AFO. 3. If an external signal source with every low voltage level is used then this signal SIETK Page 19

20 ANALOG & DIGITAL COMMNICATIONS LAB Can be amplified using the audio amplifier before connecting to the input of the FM modulator 4. Now increase the amplitude of the modulated signal to the required level. 5. The amplitude and the time duration of the modulating signal are observed Using CRO. 6. The amplitude and time duration of the modulated signal are observed using a CRO and tabulated 7. The final demodulated signal is viewed using a CRO Also the amplitude and time duration of the demodulated wave are noted down. TABULATION: Wave form Amplitude(V) Time Period(ms) Frequency(Hz) Modulating Signal Demodulated Signal RESULT: Viva Voice: 1. Define Sensitivity, Selectivity & Fidelity? 2. What is modulation & Demodulation? 3. What is the range of voice & audio? 4. What is broadcasting range of FM? 5. What is broadcasting range of AM? SIETK Page 20

21 ANALOG & DIGITAL COMMNICATIONS LAB 5. Measurement of half power beam width (HPBW) and gain of a half wave dipole antenna AIM: To Study & measure half power width and gain of a half wave dipole antenna Apparatus: 1. Gunn oscillator Isolator Pin Modulator Large Horn Antenna RF cable, L = 1 m Supports for waveguide components Stand base MF Set of microwave absorbers Set of 10 thumb screws M Remote control for rotating antenna platform Dipole antenna kit Theory: The half wave dipole is perhaps the simplest and most fundamental antenna design possible. Hertz used a dipole antenna during his initial radio experimentation. This is why a dipole is often referred to as the hertz dipole antenna. The dipole is so practical that it is utilized (in some form) in at least half of all antenna systems used today. Here are some key principles of the dipole antenna: 1.) A dipole antenna is a wire or conducting element whose length is half the transmitting wavelength. To calculate the length of a half wave dipole in free space, one may use the following equation: length (ft) = 492 / frequency (MHz). The half-wave dipole antenna is just a special case of the dipole antenna, but its important enough that it will have its own section. Note that the "half-wave" term means that the length of this dipole antenna is equal to a half-wavelength at the frequency of operation. To make it crystal clear, if the antenna is to radiate at 600 MHz, what size should the half-wavelength dipole.one wavelength at 600 MHz is dipole antenna's length is 0.25 meters. = c / f = 0.5 meters. Hence, the half-wavelength SIETK Page 21

22 ANALOG & DIGITAL COMMNICATIONS LAB Radiation pattern of half wave dipole Block Diagram SIETK Page 22

23 ANALOG & DIGITAL COMMNICATIONS LAB Procedure: 1. Arrange the setup as given in the block diagram 2. Mount Half wave dipole antenna on the transmitter mask 3. Bring the detector assembly near to main and adjust the height of both transmitting and receiving antenna 4. Keep Detector assembly away from the main unit approximately 1.5 meter and align both of them.ensure that there is no reflector sort things in the vicinity of the experiment such as a steel structure,pipes, cables etc. 5. Keep the RF level and FS adjust to minimum and unidirectional coupler switch to FWD(Forward adjustment knob). 6. Keep detector level control in the center approximately 7. Increase RF level gradually and see that there is deflection in the detector meter 8. Adjust RF level and detector level, so that the deflection in detector meter is approximately 30-35mA. 9. Align arrow mark on the disk with zero of the goniometer scale 10. Start taking the reading at the interval of 10 degree, and note the deflection on the detector assembly. 11. Using conversion chart convert ma readings into db. 12. Plot the polar graph in degrees of rotation of antenna against level in the detector in dbs Tabular column : S.No Angle in degrees Detector readings in ma Gain In db Result: Viva-Voice: 1. Define half wave dipole. 2. Draw the radiation pattern of half wave dipole antenna. 3. Give the application of half wave dipole antenna. 4. Write the frequency range of RF signal SIETK Page 23

24 ANALOG & DIGITAL COMMNICATIONS LAB 6. Measurement of radiation pattern of a loop antenna in principal planes AIM: To Study the radiation pattern of loop antenna in principal planes Apparatus: 1. Gunn oscillator Isolator Pin Modulator Large Horn Antenna RF cable, L = 1 m Supports for waveguide components Stand base MF Set of microwave absorbers Set of 10 thumb screws M Remote control for rotating antenna platform Loop antenna kit Theory: A loop antenna is a radio antenna consisting of a loop (or loops) of wire, tubing, or other electrical conductor with its ends connected to a balanced transmission line. Within this physical description there are two very distinct antenna designs: the small loop (or magnetic loop) with a size much smaller than a wavelength, and the resonant loop antenna with a circumference approximately equal to the wavelength. Small loops have a poor efficiency and are mainly used as receiving antennas at low frequencies. Except for car radios, almost every AM broadcast receiver sold has such an antenna built inside it or directly attached to it. These antennas are also used for radio direction finding. In amateur radio, loop antennas are often used for low profile operating where larger antennas would be inconvenient, unsightly, or banned. Loop antennas are relatively easy to build. A small loop antenna, also known as a magnetic loop, generally has a circumference of less than one tenth of a wavelength, in which case there will be a relatively constant current distribution along the conductor SIETK Page 24

25 ANALOG & DIGITAL COMMNICATIONS LAB Block Diagram Procedure: 1. Arrange the setup as given in the block diagram 2. Mount Loop antenna on the transmitter mask 3. Bring the detector assembly near to main and adjust the height of both transmitting and receiving antenna 4. Keep Detector assembly away from the main unit approximately 1.5 meter and align both of them.ensure that there is no reflector sort things in the vicinity of the experiment such as a steel structure,pipes, cables etc. 5. Keep the RF level and FS adjust to minimum and unidirectional coupler switch to FWD (Forward adjustment knob). 6. Keep detector level control in the center approximately 7. Increase RF level gradually and see that there is deflection in the detector meter 8. Adjust RF level and detector level, so that the deflection in detector meter is approximately 30-35mA. 9. Align arrow mark on the disk with zero of the goniometer scale 10. Start taking the reading at the interval of 10 degree, and note the deflection on the detector assembly. 11. Using conversion chart convert ma readings into db. 12. Plot the polar graph in degrees of rotation of antenna against level in the detector in dbs SIETK Page 25

26 ANALOG & DIGITAL COMMNICATIONS LAB Tabular column: S.No Angle in degrees Detector readings in ma Gain In db Result: VIVA-VOICE: 1. Draw the radiation pattern Loop antenna. 2. Give the application of Loop antenna. 3. Write the frequency range of RF signal 4. What is the need of isolator SIETK Page 26

27 ANALOG & DIGITAL COMMNICATIONS LAB DIGITAL COMMUNICATION SYSTEMS SIETK Page 27

28 ANALOG & DIGITAL COMMNICATIONS LAB 1. TIME DIVISION MULTIPLEXING AND DEMULTIPLEXING Aim: To transmit a multiplexed output of different frequency message signals through single Channel using TDM system and recover back the original message signals through a Demultiplexer at receiver end. Apparatus: 1. TDM trainer kit 2. CRO 3. Patch cords 4. Probes Theory: One of the richest benefits unearthed from Sampling is the concept of Time Division Multiplexing. In Time Division Multiplexing, use is made of the fact that narrow pulses with wide spaces between them can be used by signals from other sources. More ever, although the spaces are relatively fixed in width, pulses may be made as narrow as desired, thus permitting the generation of high-level hierarchies. Four input signals, all band limited to FS by the input filters, are sequentially sampled at the transmitter by a rotary switch or commutator. The switch makes FS revolutions per second and extracts one sample form each input during each revolution. The output at the switch is a PAM waveform-containing sample of the input signals periodically interlaced in time. The samples from adjacent input message channels are separated by Ts/M, where M is the number of input channels. A set of M pulses consisting of one sample form each of the M-input channels is called a frame. Suppose, in a 24 channel, have a sampling rate of 8000 samples per second, 8 bits(256 sampling levels) per sample, and a pulse width of approximately S. This means that the sampling interval is 1/8000 = s = 125 s, and the period required for each pulse group is 8 * = 5 s. If there was no multiplexing and only one channel was sent, the transmission would consist of 8000 frames per second, each made up of furious activity during the first 5 s and nothing at all during the remaining 120 s. This would clearly be wasteful and would represent an unnecessarily complicated method of encoding a single channel, and so this system exploits the large spaces between the pulse groups. In fact, each 125 s frame is used to provide 24 adjacent channel time slots, with the twenty-fifth slot assigned for synchronization. Each frame consists of 193 bits-24 * 8 for each channel, plus 1 for sync, and since there are 8000 frames per second; the bit rate is Mbits/sec. SIETK Page 28

29 ANALOG & DIGITAL COMMNICATIONS LAB Circuit diagram: Experimental Procedure: Multiplexing: 1. Connect the four channel inputs 250 Hz, 500Hz, 1KHz, 2 KHz to the input of transmitter CHO, CH1, CH2 and CH3 respectively. 2. Observe the Time Division Multiplexed PAM waveform at the output of the Multiplexer (TXD). 3. Observe the four different signals placed in their respective time slots. 4. Vary each of the amplitude of each channel and see the effect on the TDM waveform. Observation: 1. From the above set up, we can observe that the four different signals are interleaved in their respective time slots without overlapping each other. 2. Their positions and identification can be highlighted by reducing the other three signal amplitudes to zero and then gradually increasing them to observe them occupying their positions Demultiplexing: 1. Connect the four channel inputs 250 Hz, 500Hz, 1KHz, 2 KHz to the input of transmitter CHO, CH1, CH2 and CH3 respectively 2. Connect TXCLOCK (Transmitter Clock) to RXCLOCK (Receiver Clock). 3. Connect TXCH0 (Transmitter Sync) to RXCH0 (Receiver Sync). 4. Connect the TXD (Transmitter Data) to RXD (Receiver Data). SIETK Page 29

30 ANALOG & DIGITAL COMMNICATIONS LAB 5. Observe the multiplexed data at TDX, Transmitter Clock at TXCLOCK and Transmitter Sync at TXCHO. 6. Observe the Demultiplexed signals at the receiver across the output of fourth order low pass filter at CHO, CH1,CH2 and CH3 respectively. Observations: 1. From the above set up, we can observe that the signals are recovered at the receiver faithfully and are very distinct from each other. 2. By removing the other two lines apart from the TXD, we find that the reconstructed signals suffer from severe distortion. Waveforms: (Transmitting Signals) SIETK Page 30

31 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL Demultiplexed output: Result Viva Voice: 1. Define TDM? 2. Distinguish between the two basic multiplexing techniques? 3. In what situation multiplexing is used? 31 P a g e

32 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL PULSE CODE MODULATION Aim: To convert an analog signal into a pulse digital signal using PCM system Apparatus: 1. PCM transmitter trainer. 2. PCM receiver trainer. 3. CRO and connecting wires. Theory: Pulse-code Modulation (PCM), like PAM, is a digital communication technique that sends samples of the analog signal taken at a sufficiently high rate (higher than the Nyquist rate). In addition, PCM differs than PAM in that it quantizes the samples by constraining them to only take a limited number of values, and then converts each value into a binary string of bits that are transmitted on the communication line. Typically, in digital telephony where PCM is widely used, the sampling rate is 8 khz (higher than twice the voice band), and the quantization uses 256 levels (i.e., each sample is mapped into an 8-bit PCM code). In practice, PCM is typically combined with Time Division Multiplexing (TDM), which is the process of combining many PCM signals representing different messages and transmitting them over the same channel on a time-sharing basis. Each PCM signal is assigned a timeperiod called a slot on the transmission line, and slots are arranged in groups called frames.the main advantages of PCM transmission are: lower cost, ease of multiplexing and switching, and better noise immunity. Its main disadvantage is the stringent timing and synchronization requirements. Nowadays, PCM-TDM systems form the backbone for all digital telephony networks worldwide (refer to your textbooks for more details). Block diagram: 32 P a g e

33 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL Procedure: 1. Connect 500 Hz to CH0 and 1 KHz to CH1 2. Set the speed selection switch to FAST mode Observation: 1. Connect the scope to CH0 and CH1 for observing the channel input. 2. Connect the scope to observe the sampling clock at TP7 and TP8. 3. Observe the sampling amplifier output at TP12 with respective sampling clock. The multiplexer output shows the proper alignment of samples in their respective time slots. Also verify that the amplitude of the samples at any instant of the is equal to the amplitude of the sampled signals at that instant of time. Waveforms: Result: Viva Voice: 1. List advantages and disadvantages of digital modulation communication systems. 2. List various steps in pulse code modulation. 3. Discuss the problems associated with quantization 4. What do you mean by band rate? 5. Draw the waveforms of TDM-PCM systems. 33 P a g e

34 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL DELTA MODULATION AND DEMODULATION Aim: To transmit an analog message signal in its digital form and again reconstruct back the original analog message signal at receiver by using Delta modulator. Apparatus: 1. Delta modulator trainer kit 2. CRO 3. Probes & patch cards Theory: DM uses a single bit PCM code to achieve digital transmission of analog signal. With conventional PCM each code is binary representation of both sign and magnitude of a particular sample. With DM, rather than transmitting a coded representation of a sample a single bit is transmitted, which indicates whether the sample is smaller or larger than the previous sample. The algorithm for a delta modulation system is a simple one. If the current sample is smaller than the previous sample then logic 0 is transmitted or logic 1 is transmitted if the current sample is larger than the previous sample. The input analog is sampled and converted to a PAM signal followed by comparing it with the output of the DAC. The output of the DAC is equal to the regenerated magnitude of the previous sample which was stored in the up/down counter as a binary number. The up/down counter is incremented or decremented whether the previous sample is larger or smaller than the current sample. The up/down counter is clocked at a rate equal to the sample rate. So, the up/down counter is updated after each comparison. Block diagram: Modulator 34 P a g e

35 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL Block diagram for demodulator: Procedure: Modulator: 1. Connect PLA1 to PLAA. 2. Connect channel 1 to CRO to TPA1/TPAA ; adjust VR1 to minimum to get zero level signal. 3. Connect channel 1 to TP1 and channel 2 to TPB1 and adjust VR2 to obtain square wave half the frequency of the clock rate selected (Output at TP1). 4. Connect Channel 1 to TP2 and set voltage/div of channel 1 to mv range and Observe a triangle waveform, which is output of integrator. It can be observed that as the clock rate is increased, amplitude of triangle waveform decreases. This is called minimum step size (Clock rate can be changed by depressing SW1 switch). 5. Connect channel 1 to TPA1/TPAA; adjust VR1 in order to obtain a 1 KHz sinewave of 500 mv pp approximately. 6. Signal approximating 1 KHz is available at the integrator output (TP2); this signals obtained by integrating the digital output resulting from Delta Modulation. 35 P a g e

36 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL Connect channel 1 to TP2 and channel 2 to TPB1; it can be observed that the digital high makes the integrator output to go upwards and digital low makes the integrator output to go downwards. 8. With an oscilloscope displaying three traces,, it is possible to simultaneously observe the input signal of the modulation, the digital output of the modulator and the signal obtained by the integration from the modulator digital output. 9. Notice that, when the output (Feedback signal) is lower than the analog input the digital output is high, whenever it is low when the analog input is lower than the integrated output. 10. Increase the amplitude of 1 KHz sinewave by rotating VR1 to1 Vpp and observe that the integrator output follows the input signal. 11. Increase the amplitude of 1 KHz sinewave further high, and observe that the integrator output cannot follow the input signal. State the reason. 12. Repeat the above mentioned procedures with different signal sources and selecting different clock rates and observe the response of the linear Delta Modulator Demodulator: 1. Prearrange the connections of Linear Delta Modulator. 2. Connect PLB1 (Digital o/p of Delta Modulator) to PLBB (i/p of Linear Delta Modulator). 3. Connect PLC1 (Linear Delta Demodulator output) to either PLCA (i/p of fourth order LPF) or PLCB (i/p of second order LPF). Observations: Observe the reconstructed output of the forth order LPF at TPD1 and also observet he out of the second order filter at TPD2. Waveforms: Result: 36 P a g e

37 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL Viva -Voice 1. What is a Modulator? 2. Define Bit Rate? 3. Explain Delta Modulation Technique? 4. Explain delta sigma Modulation? 5. What are the Applications of Delta modulations? 37 P a g e

38 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL FREQUENCY SHIFT KEYING Aim: To generate the frequency shift keying signal for a given binary data and also demodulate the original data input. Apparatus: 1. Band Pass modulator and Demodulator trainer kit. 2. C.R.O 3. Patch Cards and probes Theory: Communication systems often involve modulation of a carrier, which results, of course, in a band pass waveform. Radio & Television signals are good examples involving analog messages. A good example where the message is digital is the modem, a device used to connect a remote computer terminal to the main computer. The modulation-de modulation apparatus modulates a carrier with the terminal s data stream for transmission to the computer (often over telephone lines) and recovers the data stream sent by the computer via a similar modulation. Band pass Modulation is the process by which an information signal is converted to a sinusoidal waveform; for digital modulation, such a sinusoid of duration T is referred to as a digital symbol. The sinusoid has just three features that can be used to distinguish it from other sinusoids: amplitude, frequency, and phase. Thus band pass modulation can be defined as the process whereby the amplitude, frequency, or phase of a RF carrier, or a combination of them, is varied in accordance with the information to be transmitted. The general form of the carrier wave, C (t), is as follows: C(t) = A(t) cos θ(t) Where A(t) is the time-varying amplitude and θ(t) is the time-varying angle. It is convenient to write In this type of modulation, the modulated output shifts between two frequencies for all one to zero transitions. Let the two carrier frequencies be represented by 1 and 2 and then we have: M (t)=a (t) cos 1t, if the data is one =A (t) cos 2t, if the data is zero where 0 is the radian frequency of the carrier and Φ(t) is the phase. The terms f and will each be used to denote the frequency. 38 P a g e

39 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL Block diagram: Experimental Procedure: FSK Modulator: Connect SIN1 to the INPUT-1 of the Modulator Connect SIN2 to the INPUT-2 of the Modulator Connect data to the control input of the Modulator Connect the scope to the Control Input and the other channel to the Modulated output FSK Demodulator: Establish the same connections for FSK modulation in DCLT 005 Set DCLT-005 in conjunction with DCLT 005 Connect the FSK Modulated output to the FSK I/P of the FSK Demodulator (DCLT 006) Connect the scope to the CONTROL INPUT and the DATA OUTPUT 39 P a g e

40 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL Observations: 1. Observe the FSK Modulated output and the modulating data in the two channels of the oscilloscope. 2. Observe the incoming modulated carrier and recovered data with respect to the modulating data. Waveforms: Result:. Viva Voice: 1. Compare FSK and FM? 2. Compare ASK and FSK? 3. What are the different techniques to demodulate FSK? 4. Define FSK? 40 P a g e

41 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL QPSK MODULATION AND DEMODULATION Aim: To generate a QPSK for a given binary digital signal and Observe. Demodulate the same QPSK to get back the Original digital signal, using carrier receiving circuit and Demodulator. Components Required: 1.Patch chords, 2.Signal generator, 3.CRO, 4.Probes Theory: QPSK is another form of angle-modulated, constant-amplitude digital modulation. It is an M-ary encoding technique where M=4. With QPSK four output phases are possible for a single carrier frequency. Two bits are clocked into the bit splitter. After both bits have been serially inputted, they are simultaneously parallel outputted. One bit is directed to the I channel and the other to the Q channel. The I bit modulates a carrier that is in phase with the reference oscillator and the Q bit modulates a carrier that is 900 out of phase with the reference carrier. QPSK modulator is two BPSK modulators combined in parallel. The input QPSK signal is given to the I and Q product detectors and the carrier recovery circuit. The carrier recovery circuit produces the original transmit carrier oscillator signal. The recovered carrier must be frequency and phase coherent with the transmit reference carrier. The QPSK signal is demodulated in the I and Q product detectors, which generate the original I and Q data bits. The output of the product detectors are fed to the bit combining circuit, where they are converted from parallel I and Q data channels to a single binary output data stream. Procedure: 1. Connect the binary input data to I-channel. 2. Connect the binary input data to Q-channel. 3. Connect the sine wave input to balanced modulator (I channel) as a carrier signal and to sine wave input to balanced modulator (Q channel) as a carrier signal. 4. Switch on the power supply. 5. Display binary input data on CRO. Adjust pot1 and pot3 to get bipolar data. 6. Adjust gain control pot to set equal amplitude in I and Q channel. 7. Obtain QPSK signal. 8. Connect the QPSK to input of QPSK demodulator. 9. Obtain the demodulated QPSK signal 41 P a g e

42 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL Block Diagram: Model waveforms: 42 P a g e

43 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL Tabular Column: S.No Name of the signal Amplitude in V Time period in Sec Frequency in Hz 1 Modulating Signal 2 Carrier Signal 3 Modulated Signal 4 Demodulated Signal Result: Viva -Voice 1. What is the difference between PSK&QPSK? 2. What is the band width requirement of a QPSK? 3. Explain the operation of QPSK detection? 4. What are the advantages of QPSK? 5. What is meant by differential encoding 43 P a g e

44 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL DIFFERENTIAL PHASE SHIFT KEYING Aim: To generate differentially phase shift keying signal and also demodulate the original Binary data. Apparatus: 1. DPSK modulation and demodulation trainer kit 2. CRO 3. Patch cards Theory: DPSK may be viewed as the non-coherent version of PSK. It eliminates the need for a coherent reference signal at the receiver by combining two basic operations at the transmitter: 1. Differential encoding of the input binary wave and 2. Phase-Shift Keying hence, the name, differential phase shift keying (DPSK). In effect to send symbol 0, we phase advance the current signal wave-form by 180 0, and to send symbol 1, we leave the phase of the current signal waveform unchanged. The receiver is equipped with a storage capability, so that it can measure the relative phase difference between the waveforms received during two successive bit intervals. Provided that the unknown phase θ contained in the received wave varies slowly, the phase difference between wave forms received in two successive bit intervals will be independent of θ. 44 P a g e

45 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL Block diagram: Data Simulator UNITED CARRIER ELECTROTECHNOLOGIES GENERATION LOGIC DCL s-clock CODING LOGIC s-data INPUT UNIPOLAR TO BI POLAR OUTPUT SIN1 SIN2* SIN CARRIER MODULATION 2 NRZ- CLOCK INPUT 1 NRZ- M NRZ-S URZ INPUT BI POLAR TO UNIPOLAR INPUT 2 CONTROL INPUT MODULATION BIO-L BIO- BIO-S DATA OUTPUT AMI D P SK RESET SERIAL DATA S6 T6 DPSK DPSK CONTROL M O D S - CLOCK S5 T5 ENCODER T7 S7 S-DATA WITH ONE BIT DELAY D P SK S10 T10 PLL CLOCK FROM DCLT- 006 TP12 CLOCK S15 T15 DPSK MODULATED DATA FROM DCLT-006 DPSK T13 S13 45 P a g e

46 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL Procedure: (Modulator) Establish the connection for DPSK modulation and connect the DCLT 006 in conjunction with the DCLT- 005 & DCLT-011 Feed the PSK Modulated Output to the PSK I/P of the PSK Demodulator of DCLT 006 Connect the scope to the PSK I/P and the DATA O/P for PSK Demodulated o/p Observe the PSK Demodulated output w.r.t the control input of the Modulator DCLT-005 Feed the Demodulated DPSK signal to DCLT-011 (S15) and the recovered clock to the DPSK Decoder at S10. Connect the Scope to the S-Data of DCLT-005 and Decoded S-Data of DCLT-011 Refer page for connection Diagram. Observations: The DPSK modulated output and the Demodulating data using the two channels of the oscilloscope. The DPSK Demodulated Data with DPSK Coded Data. The S-Data with DPSK Decoded Data. (with 1 bit delay) Wave forms: Result: Viva -Voice 1. Explain DPSK Modulation technique? 2. Difference between DPSK & PSK? 3. The Non coherent Version of PSK is known as 4. Define Modulation? 5. Define Modulation Index? 46 P a g e

47 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL DIGITAL COMMUNICATIONS USING MATLAB 47 P a g e

48 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL TIME DIVISION MULTIPLEXING Aim: To perform the generation of Time division multiplexing using MATLAB Apparatus: 1. Hardware Tools: Computer system 2. Software Tool: MATLAB 7.0 Program: % % % % % % % % % % % % % % % % % % % % % Code for Time Division Multiplexing clc; close all; clear all; % Signal generation x=0:.5:4*pi; sig1=8*sin(x); l=length(sig1); sig2=8*triang(l); % siganal taken upto 4pi % generate 1st sinusoidal signal % Generate 2nd traingular Sigal % Display of Both Signal subplot(2,2,1); plot(sig1); title('sinusoidal Signal'); ylabel('amplitude--->'); xlabel('time--->'); subplot(2,2,2); plot(sig2); title('triangular Signal'); ylabel('amplitude--->'); xlabel('time--->'); % Display of Both Sampled Signal subplot(2,2,3); stem(sig1); title('sampled Sinusoidal Signal'); ylabel('amplitude--->'); xlabel('time--->'); subplot(2,2,4); stem(sig2); title('sampled Triangular Signal'); ylabel('amplitude--->'); xlabel('time--->'); l1=length(sig1); l2=length(sig2); for i=1:l1 48 P a g e

49 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL sig(1,i)=sig1(i); sig(2,i)=sig2(i); end % Making Both row vector to a matrix % TDM of both quantize signal tdmsig=reshape(sig,1,2*l1); % Display of TDM Signal figure stem(tdmsig); title('tdm Signal'); ylabel('amplitude--->'); xlabel('time--->'); % Demultiplexing of TDM Signal demux=reshape(tdmsig,2,l1); for i=1:l1 sig3(i)=demux(1,i); % Converting The matrix into row vectors sig4(i)=demux(2,i); end % display of demultiplexed signal figure subplot(2,1,1) plot(sig3); title('recovered Sinusoidal Signal'); ylabel('amplitude--->'); xlabel('time--->'); subplot(2,1,2) plot(sig4); title('recovered Triangular Signal'); ylabel('amplitude--->'); xlabel('time--->'); 49 P a g e

50 Amplitude---> Amplitude---> Amplitude---> Amplitude---> Amplitude---> ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL OUTPUTS: 10 Sinusoidal Signal 8 Triangular Signal Time---> Sampled Sinusoidal Signal Time---> Time---> Sampled Triangular Signal Time---> 8 TDM Signal Time---> 50 P a g e

51 Amplitude---> Amplitude---> ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL Recovered Sinusoidal Signal Time---> Recovered Triangular Signal Time---> Results: 51 P a g e

52 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL Pulse code modulation Aim: To perform the generation of Pulse code modulation using MATLAB Apparatus: 1. Hardware Tools: Computer system 2. Software Tool: MATLAB 7.0 Program : % % % % % % % % % % % % % % % % % % % % % % Code for Pulse Code Modulation clc; close all; clear all; n=input('enter n value for n-bit PCM system : '); n1=input('enter number of samples in a period : '); L=2^n; % % Signal Generation % x=0:1/100:4*pi; % y=8*sin(x); % Amplitude Of signal is 8v % subplot(2,2,1); % plot(x,y);grid on; % Sampling Operation x=0:2*pi/n1:4*pi; % n1 nuber of samples have tobe selected s=8*sin(x); subplot(3,1,1); plot(s); title('analog Signal'); ylabel('amplitude--->'); xlabel('time--->'); 52 P a g e

53 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL subplot(3,1,2); stem(s);grid on; title('sampled Sinal'); ylabel('amplitude--->'); xlabel('time--->'); % Quantization Process vmax=8; vmin=-vmax; del=(vmax-vmin)/l; part=vmin:del:vmax; % level are between vmin and vmax with difference of del code=vmin-(del/2):del:vmax+(del/2); % Contaion Quantized valuses [ind,q]=quantiz(s,part,code); % Quantization process % ind contain index number and q contain quantized values l1=length(ind); l2=length(q); for i=1:l1 if(ind(i)~=0) % To make index as binary decimal so started from 0 to N ind(i)=ind(i)-1; end i=i+1; end for i=1:l2 if(q(i)==vmin-(del/2)) % To make quantize value inbetween the levels q(i)=vmin+(del/2); end end subplot(3,1,3); stem(q);grid on; % Display the Quantize values title('quantized Signal'); ylabel('amplitude--->'); xlabel('time--->'); 53 P a g e

54 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL % Encoding Process figure code=de2bi(ind,'left-msb'); % Cnvert the decimal to binary k=1; for i=1:l1 for j=1:n coded(k)=code(i,j); % convert code matrix to a coded row vector j=j+1; k=k+1; end i=i+1; end subplot(2,1,1); grid on; stairs(coded); % Display the encoded signal axis([ ]); title('encoded Signal'); ylabel('amplitude--->'); xlabel('time--->'); % Demodulation Of PCM signal qunt=reshape(coded,n,length(coded)/n); index=bi2de(qunt','left-msb'); % Getback the index in decimal form q=del*index+vmin+(del/2); % getback Quantized values subplot(2,1,2); grid on; plot(q); % Plot Demodulated signal title('demodulated Signal'); ylabel('amplitude--->'); xlabel('time--->'); INPUT: Enter n value for n-bit PCM system : 5 Enter number of samples in a period : P a g e

55 Amplitude---> Amplitude---> Amplitude---> Amplitude---> Amplitude---> ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL OUTPUT: 10 0 Analog Signal Time---> Sampled Sinal Time---> Quantized Signal Time---> Encoded Signal Time---> Demodulated Signal Time---> Results: 55 P a g e

56 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL Delta Modulation Aim: To perform the generation of Delta modulation using MATLAB Apparatus: 1. Hardware Tools: Computer system 2. Software Tool: MATLAB 7.0 Program: % DELTA MODULATiON clc; clear all; close all; a=2; t=0:2*pi/50:2*pi; x=a*sin(t); l=length(x); plot(x,'r'); delta=0.2; hold on xn=0; for i=1:l; if x(i)>xn(i) d(i)=1; xn(i+1)=xn(i)+delta; else d(i)=0; xn(i+1)=xn(i)-delta; end end stairs(xn) hold on for i=1:d if d(i)>xn(i) d(i)=0; xn(i+1)=xn(i)-delta; else d(i)=1; xn(i+1)=xn(i)+delta end end plot(xn,'c') legend('analog signal','delta modulation','demodulation') title('delta MODULATION / DEMODULATION ') 56 P a g e

57 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL OUTPUT: DELTA MODULATION / DEMODULATION Analog signal Delta modulation Demodulation RESULT: 57 P a g e

58 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL Frequency shift keying Aim: To perform the generation of Frequency shift keying using MATLAB Apparatus: 1. Hardware Tools: Computer system 2. Software Tool: MATLAB 7.0 Program: clc; close all; clear all; x=input('enter the binary input'); l=length(x); for i=1:1:l m(((i-1)*100)+1:i*100)=x(i); end figure; subplot(4,1,1); plot(m); xlabel('time'); ylabel('amplitude'); title('modulating signal'); f=100; t=0:(1/f):(l-(1/f)); f1=10; f2=5; c1=sin(2*pi*f1*t); y1=m.*c1; subplot(4,1,2); plot(t,y1); xlabel('time'); ylabel('amplitude'); for j=1:l if x(j)==1 x(j)=0; else x(j)=1; end m1((j-1)*100+1:j*100)=x(j); end c2=sin(2*pi*f2*t); y2=m1.*c2; subplot(4,1,3); plot(t,y2); xlabel('time'); 58 P a g e

59 ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL ylabel('amplitude'); y=y1+y2; subplot(4,1,4); plot(t,y); xlabel('time'); ylabel('amplitude'); title('fsk modulated wave'); r=randn(size(y)); F=y+r; figure; subplot(3,1,1); plot(f); xlabel('time'); ylabel('amplitude'); title('noise added FSK signal'); l1=length(f); t1=0:0.01:.99; r1=sin(2*pi*f1*t1); r1=fliplr(r1); l2=length(r1); l3=l1+l2-1; u=fft(f,l3); v=fft(r1,l3); k1=u.*v; k11=ifft(k1,l3); r2=sin(2*pi*f2*t1); r2=fliplr(r2); w=fft(r2,l3); k2=u.*w; k22=ifft(k2,l3); k=k11-k22; subplot(3,1,2); plot(k); xlabel('time'); ylabel('amplitude'); title('correlated signal'); for z=1:l t(z)=k(z*100); if t(z)>0 s(z)=1; else s(z)=0; end end subplot(3,1,3); stem(s); xlabel('time'); 59 P a g e