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EX NO: 1 AM MODULATION AND DEMODULATION
DATE:
AIM:
To generate the amplitude modulated wave and to plot the graphs of modulating, modulated and demodulated waves.
APPARATUS REQUIRED:
Trainer kit
• Power cords
• Power supply
• Patch cords
• CRO
THEORY:
AMPLITUDE MODULATION:
Amplitude Modulation is a process by which amplitude of the carrier signal is varied in accordance with the instantaneous value of the modulating signal, but frequency and phase of carrier wave remains constant.
The modulating and carrier signal are given by Vm(t) = Vm sinmt
VC(t) = VC sinCt
The modulation index is given by, ma = Vm / VC.
Vm = Vmax – Vmin and VC = Vmax + Vmin
The amplitude of the modulated signal is given by, VAM(t) = VC (1+ma sinmt) sinCt
Where
Vm = maximum amplitude of modulating signal
VC = maximum amplitude of carrier signal
Vmax = maximum variation of AM signal
Vmin = minimum variation of AM signal
PROCEDURE:
A.AMPLITUDE MODULATION
1. Connect the mains cord of the trainer unit to AC 220V,50Hz SUPPLY.
2. Switch ON the trainer kit. The neon lamp will glow indicating that the unit is ready for operation.
3. Observe the waveforms of modulating signal and carrier signal in an oscilloscope .
4. USING patch cords connect the modulating signal and the carrier signal to „AM MODULATION‟.
5. Observe the amplitude modulated output waveform across sockets marked „ AM OUTPUT‟.
6. Vary the amplitude of modulating signal and observe the different modulation index of 100%, less than 100%.
B. AM DEMODULATION
1. Set the amplitude of modulating and carrier signal in amplitude modulation as follows Modulating signal:1.5 vp-p carrier signal: vp-p
2. Using patch cords, connect the „AM OUTPUT‟ from the AM Modulation to the sockets „AM INPUT‟
In the AM Demodulation.
3. Observe the demodulated output waveform across sockets marked „DEMOD OUTPUT‟.
FREQUENCY MODULATION & DEMODULATION
DATE:
AIM
To verify the functioning of frequency modulation & demodulation and to calculate the modulation index.
APPARATUS REQUIRED
1. Frequency modulation & demodulation trainer kit,
2. C.R.O (20MHz),
3. Function generator (1MHz),
4. Connecting chords & probes.
THEORY
This kit consists of wired circuitry of:
1. AF generator, 2. Regulated power supply, 3. Modulator, 4. Demodulator.
1. AF GENERATOR
This is an op-amp placed wein bridge oscillator. A FET input quad Op-Amp (ICTL084) is used here to generate low frequency signals of 500 Hz and 5KHz to use as modulating signal. In this experiment, a switch is provided to change the frequency. Required amplification is provided to avoid loading effect.
2. REGULATED POWER SUPPLY
This consists of bridge rectifier, capacitor filters and three terminal regulators to provide required dc voltages in the circuit i.e. +15 V, -15 V, +5V .
3. MODULATOR
This has been developed using XR-2206 integrated circuit. The IC XR-2206 is a monolithic Function generator; the output waveforms can be both amplitude and frequency modulated by an external voltage. Frequency of operation can be selected externally over a range of 0.01 MHz. The circuit is ideally suited for communications, instrumentations and function generator applications requiring sinusoidal tone,
AM, FM or FSK generation. In this experiment, IC XC-2206 is connected to generate sine wave, which is used as a carrier signal. The amplitude of carrier signal is 5vPP of 100 KHz frequencies.
4. DEMODULATOR
This had been developed using LM4565 integrated circuit. The IC LM565 is a general-purpose phase locked loop containing a stable, highly linear voltage controlled oscillator for low distortion FM demodulation. The VCO free running frequency f0 is adjusted to the center frequency of input frequency modulated signal i.e. carrier frequency which is of 100 KHz. When FM signal is connected to the demodulator input, the deviation in the input signal (FM signal) frequency which creates a DC error voltage at output of the phase comparator which is proportional to the change of frequency δf. This error voltage pulls the VCO to the new point. This error voltage will be the demodulated version of the frequency modulated input signal.
PROCEDURE
1. Switch on the power supply of the kit (without making any connections).
2. Measure the frequency of the carrier signal at the FM output terminal with input terminals open and plot the same on graph.
3. Connect the circuit as per the given circuit diagram.
4. Apply the modulating signal of 500HZ with 1Vp-p.
5. Trace the modulated wave on the C.R.O & plot the same on graph.
6. Find the modulation index by measuring minimum and maximum frequency deviations from the carrier frequency using the CRO.
Mr = S/f = maximum Frequency deviation / modulating signal frequency
7. Repeat the steps 5& 6 by changing the amplitude and /or frequency of the modulating Signal.
8. For demodulation apply the modulated signal as an input to demodulator circuit and compare the demodulated signal with the input modulating signal & also draw the same on the graph.
3 PULSE AMPLITUDE MODULATION AND DEMODULATION
DATE:
AIM:
To generate and to detect the pulse amplitude, pulse width, pulse position modulated wave and to plot the graphs of modulated and demodulated waves.
APPARATUS REQUIRED:
Trainer kit
Power cords
Power supply
Patch cords
CRO
STS2110 trainer kit
THEORY:
PULSE AMPLITUDE MODULATION (PAM):
Pulse amplitude modulation is defined as an analog modulation technique in which the signal is sampled at regular intervals such that each sample is proportional to the amplitude of the signal, at the instant of sampling.
PULSE WIDTH MODULATION (PWM):
Pulse width modulation is defined as an analog modulation technique in which the width of each pulse is made proportional to the instantaneous amplitude of the signal at the sampling instant.
PULSE POSITION MODULATION (PPM):
Pulse position modulation is defined as an analog modulation technique in which the signal is sampled at regular intervals such that the shift in position of each sample is proportional to the instantaneous value of the signal at the sampling instant.
Objective :
Study of pulse amplitude modulation & demodulation with sample, sample & hold & flat top
Procedure :
1. Connect the circuit as shown in Fig and also described below for clarity.
a. Output of sine wave to modulation signal IN in PAM block keeping the switch in 1 KHz position.
b. 8 KHz pulse output to pulse input.
c. Connect the sample output low pass filter input.
d. Output of low pass filter to input of AC amplifier. Keep the gain pot in AC amplifier block in max position.
2. Follow the steps of experiment 1.
3. Monitor the output of AC amplifier. It should be a pure sine wave similar to input.
4. To vary the amplitude of input, the amplitude of output will vary.
5. Similarly connect the sample & hold & flat top outputs to low pass filter and see the demodulated waveform at the output of AC amplifier.
6. Switch „On‟ the switched faults No. 1, 2, 3, 4, 5 & 8 one by one and see their effects on output.
7. Try to locate the fault and explain the reason behind them.
8. Switch „Off‟ the power supply.
OBJECTIVE :
Study of ppm using sine wave input
Procedure :
1. Connect the circuit as shown in Figure 20 and also described below for clarity.
a. Input of pulse position modulation blocks to sine wave output of FG block.
2. Switch „On‟ the power supply.
3. Keep the oscilloscope at 0.5mS / div, time base speed and in X-5 mode, and observe the pulse position modulated waveform at the pulse position modulation block output.
4. Vary the amplitude of sine wave and observe the pulse position modulation, keep the amplitude preset in center. Here you can best observe the pulse modulation.
5. Switch „On‟ fault No. 1, 2, & 6 one by one & observe their effects in pulse position modulation output and try to locate them.
6. Switch „Off‟ the power supply.
Study of PPM Demodulation
Procedure :
1. Connect the circuit as shown in Figure 21 and also described below for clarity.
a. Sine wave of 1 KHz to input of PPM block.
b. Output PPM block to input of low pass filter.
c. Output of low pass filter to input of AC amplifier.
d. Keep the gain potentiometer in amplifier block at maximum position.
2. Switch „On‟ the power supply.
3. Perform experiment 5.
4. Observe the waveform at the TP12 output of low pass filter block.
5. Then observe the demodulated output at TP14 output of AC amplifier.
6. Switch „On‟ fault No. 1, 2, 6 & 8 one by one & observes their effect on demodulated waveform & tries to locate them.
7. Switch „Off‟ the power supply.
OBJECTIVE :
Study of PWM Using Different Sampling
PROCEDURE :
1. Connect the circuit as shown in Figure 22 and also described below for clarity.
a. 1 KHz sine wave output of function generator block to modulation input of PWM block.
b. 64 KHz square wave output to pulse input of PWM block.
2. Switch „On‟ the power supply.
3. Observe the output of PWM block.
4. Vary the amplitude of sinewave and see its effect on pulse output.
5. Vary the sinewave frequency by switching the frequency selector switch to 2 KHz.
6. Also, change the frequency of the pulse by connecting the pulse input to different pulse frequencies viz. 8 KHz, 16 KHz, 32 KHz and see the variations in the PWM output.
7. Switch „On‟ fault No. 1, 2, & 5 one by one & observes their effect on
PWM output and tries to locate them.
8. Switch „Off‟ the power supply.
PULSE CODE MODULATION
DATE:
AIM:
To generate and detect the pulse code modulation waveforms and to plot the modulated
waveforms with AF signal and DC input.
APPARATUS REQUIRED:
Trainer kit
Power cords
Power supply
Patch cord
THEORY:
Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, Compact Discs, digital telephony and other digital audio applications. In a PCM stream, the amplitude of the analog signal is sampled regularly at uniform intervals, and each sample is quantized to the nearest value within a range of digital steps.PCM streams have two basic properties that determine their fidelity to the original analog signal: the sampling rate, the number of times per second that samples are taken; and the bit depth, which determines the number of possible digital values that each sample can take. It is a digital representation of an analog signal where the magnitude of the signal is sampled regularly at uniform intervals, then quantized to a series of symbols in a digital (usually binary) code. PCM has been used in digital telephone systems and is also the standard form for digital audio in computers and the compact disc red book format. It is also standard in digital video, for example, using ITU-R BT.601. However, straight PCM is not typically used for video in consumer applications such as DVD or DVR because it requires too high a bit rate (PCM audio is supported by the DVD standard but rarely used). Instead, compressed variants of PCM are normally employed. However, many Blu-ray Disc movies use uncompressed PCM for audio. Very frequently, PCM encoding facilitates digital transmission from one point to another (within a given system, or geographically) in serial form. PCM modulation is a kind of source coding. The meaning of source coding is the conversion from analog signal to digital signal. After converted to digital signal, it is easy for us to process the signal such as encoding, filtering the unwanted signal and so on. Besides, the quality of digital signal is better than analog signal. This is because the digital signal can be easily recovered by using comparator. Information in an analog form cannot be processed by digital computers so it's necessary to convert them into digital form.
Objective :
Study of Time Division Multiplexing
Procedure :
1. Set up the following initial conditions on ST2153:
a) Mode Switch in fast position
b) DC 1 & DC2 Controls in function generator block fully clockwise.
c) ~ 1 KHz and ~2 KHz control levels set to give 10Vpp.
d) Pseudo - random sync code generator on/'Off' switch in 'Off' Position.
e) Error check code generator switch A & B in A=0 & B=0 position ('Off'
Mode)
f) All switched faults 'Off'.
2. First, connect only the 1 KHz output to CH 0
3. Turn ON the power. Check that the PAM output of 1 KHz sine wave is
available at TP15 of the ST2153.
4. Connect channel 1 of the oscilloscope to TP10 & channel 2 of the oscilloscope
to TP15. Observe the timing & phase relation between the sampling signal
TP10 & the sampled waveform at TP15.
5. Turn 'Off' the power supply. Now connect also the 2 KHz supply to CH 1.
6. Connect channel 1 of the oscilloscope to TP12 & channel 2 of the oscilloscope
to TP15.
7. Observe & explain the timing relation between the signals at TP10, 5, 6, 12&15
EX NO: 5 a DELTA MODULATION & DEMODULATION
DATE:
AIM:
To generate and detect the adaptive delta modulated waveforms and to plot the modulated and demodulated waveforms.
APPARATUS REQUIRED:
Trainer kit
Power cords
Power supply
Patch cord
THEORY:
The delta encoding process samples, quantises and encodes the intelligence signal into a digital signal. The instantaneous voltage of an intelligence signal is compared to the feedback signal. The result of the comparision is quantised and encoded and appears as a logic 1 or logic 0, depending on which sample voltage is greater. The encoded logic levels make up the digital signal. Delta modulation requires simple hardware for encoding an intelligence signal. The encoding process consists of a digital sampler and an integrator as shown in figure. The digital sampler consists of a comparator and a D- type flip-flop. The intelligence signal drives the non-inverting input of the comparator. The feedback signal from the integrator drives the inverting input of the comparator. During each clock signal the comparator compares the present sample voltage of the intelligence signal with the feedback signal. The feedback signal is an approximate voltage of the previous intelligence signal sample. If the intelligence signal is greater than the feedback signal, the comparator outputs a logic 1 to the D input of the D-type flip-flop. If the intelligence signal is less than the feedback signal the comparator outputs an negative signal to the D-type flip flop. The Q output of the D-type flip-flop is 0v on the leading edge of the next clock pulse. The Q output of the D type flip-flop is the digital signal. The digital signal contains the information needed by an integrator to generate the approximate intelligence signal (feedback signal). The integrator outputs an upward sloping ramp as the feedback signal when the digital signal is at logic 1. When the digital signal is at logic0, the integrator outputs a downward sloping ramp as the feedback signal. The digital signal is the difference between the intelligence and feedback signals
OBJECTIVE :
STUDY OF DELTA MODULATION DEMODULATION PROCEDURE :
1. Connect the power supply
2. Make connections on the board as shown in the figure 7
3. Ensure that the clock frequency selector block switches A & B are in A = 0 and B = 0 position.
4. Ensure that integrator 1 block's switches are in following position:
a) Gain control switch in left-hand position (towards switch A & B).
b) Switches A & B in A=0 and B=0 positions.
5. Ensure that the switches in integrator 2 blocks are in following position:
a) Gain control switch in right-hand position (towards switch A & B)
b) Switches A & B are in A = 0 and B = 0 positions.
6. Take the input to 0V. So connect the '+' input of the delta modulator's voltage comparator to 0V and monitor on an oscilloscope the output of integrator 1 (TP13) and the output of the transmitter's unipolar to bipolar converter (TP 29)
9. Adjust the transmitter's level changer preset until the output of integrator 1 (TP
13) is a triangular wave centered around 0 Volts.
10. Examine the signal at the output of integrator 2 (TP 41) at the receiver. This should be a triangular wave, with step size equal to that of integrator 1, and ideally centre around 0 Volts.
Outputs at TP 13 and TP 41 respectively
Volts/Div: 1V Clock Frequency: 50 KHz
Time/Div: 20 usec Input Signal : 0V
11. Disconnect the voltage comparators '+' input from 0V, and reconnect it to the ~1 KHz output from the function generator block; the modulator's analog input signal is now a 1 KHz sine wave. .
12. Display the data of the transmitter's bistable (at TP 19), together with the analog input at TP 15 (again trigger on this signal).
The output of the voltage comparator (TP 16), the bistable's clock input (TP 19), and the unipolar to bipolar output (TP 29)
ADAPTIVE DELTAMODULATION & DEMODULATION
DATE:
AIM:
To generate and detect the adaptive delta modulated waveforms and to plot the modulated and demodulated waveforms.
APPARATUS REQUIRED:
Trainer kit
Power cords
Power supply
Patch cords
CRO
THEORY OF ADAPTIVE DELTA MODULATION
As it has been seen, delta modulation system is unable to chase the rapidly changing information of the analog signal, which gives rise to distortion & hence poor quality reception. This is known as slope overloading phenomenon. The problem can be overcome by increasing the integrator gain (i.e. step-size). However, using high step-size integrator would lead to a high quantization noise.
Quantization Noise:
It is defined as error introduced between the original signal, & the quantized signal due to the fixed step size in which the signal (quantized) is incremented. As the error is random in nature & hence unpredictable, it can be treated as noise. High quantization noise may play havoc on small amplitude signals. The solution to this problem is to increase the integrator gain for fast-changing inputs & to use normal gain for small amplitude signals.
The basic idea is to increase the integrator gain (it is doubled on this trainer) when slope overload occurs. If still it is unable to catch up with the signal, the integrator gain is doubled again. The integrator on board has four available gains standard, standard X2, standard X4, and standard X8. The integrator thus adopts it self to the gain where its lowest value can just overcome the slope overloading effect
Study of Adaptive Delta Modulation and emodulation
Procedure :
1. Connect the power supply.
2. Connect the board as per figure
3. Ensure that the clock frequency selector switches A & B are in A=0 & B=0
position.
4. Ensure that the switches in transmitter’ integrator gain control block are in following positions.
a) Gain control switch at the L.H.S. position. (towards switches A & B)
b) Switches A & B in position A=0 & B=0.
5. Ensure that the switches in receiver's integrator gain control block are in
following positions:
a) Gain control switches at the R.H.S. position. (towards switches A & B)
b) Switches A & B in Position A=0 & B=0.
6. Turn ON the supply.
7. Adjust the outputs of function, generator block namely 1 KHz to 4 KHz to
10Vpp
8. As the gain control switch is towards A & B switches, the gain setting is still manual, connect the voltage comparator's +ve input to 0V & check whether the
modulator & demodulator are balanced for correct operation as in delta modulation experimentation.
Change the clock frequency selector switches to the A=1, B=1, positions
(400 KHz Clock Frequency) before continuing.
9. Disconnect the voltage comparators '+' input from 0V and reconnect it to the
4 KHz output from the function generator block.
10. Monitor the 4 KHz analog input at TP14 and the output of integrator 1 at TP13.
Note that slope overloading is still occurring, as indicated by the fact that the
integrator's output is not an approximation of the analog input signal.
11. At the transmitter, move the slider of the gain control switch in the integrator 1
block to the right-hand position (towards the sockets labeled A, B). At the
receiver, move the slider of the gain control switch in the integrator 2 block to
the left-hand position (again towards the sockets labeled A, B). The gain of each
integrator is now controlled by the outputs of the counter connected to it.
12. Once again examine the 4 KHz analog input at TP14 and the output of
integrator 1 at TP13, noting that the" slope overloading problem has been
eliminated, and that the integrator's output once again follows the analog input
signal. Again, it may be necessary to adjust slightly the transmitter's level adjust
preset, in order to obtain a stable trace of the integrator's output signal.
13. Compare the output of integrator 1 (TP13) with that of integrator 2 (TP41);
noting that, both are identical in appearance as expected.
Output waveforms at TP13 and TP43 respectively
Volts/Div: 5V Clock Frequency: 400 KHz
Time/Div: 200usec Input Signal frequency: 4 KHz, 10Vpp
Automatic gain control of Tx. & Rx. Integrators
14. Examine the output of the low pass filter (TP42) and the output of integrator 2
(TP41). The filter has removed the high-frequency components from the
integrator's output signal, to leave good, clean 4 KHz sine wave.
15. Compare the original 4 KHz analog input signal (at TP15) with the output signal from the receiver's low pass filter at TP43).
16. Disconnect the voltage comparator’s '+' input from the 4 KHz function generator output, and reconnected it in turn to the 3 KHz, 2 KHz and 1 KHz outputs, noting in each case that the demodulator’s output signal is identical to the modulator's input signal, but delayed in time.
Output waveforms at TP13 and TP43 respectively
Volts/Div: 5V Clock Frequency: 400 KHz
Time/Div: 200usec Input Signal frequency: 1 KHz, 10Vpp
Automatic gain control of Tx. & Rx. Integrators
17. The adaptive delta modulator/demodulator system has therefore eliminated slope-overloading problems. To examine in details how it does this, reconnect the voltage comparator's '+' input to the function generator's 4 KHz output, then reduce the system clock (i.e. sampling) frequency to 50 KHz, by putting the clock frequency selector switches in the A=0, B=0 positions. Although a 50 KHz sampling frequency is too low to ensure that an undistorted output is obtained from the demodulator's low pass filter, it does increase the step size to a level, which makes it easier to understand how the system is operating.
18. Monitor the 4 KHz analog input signal at TP14 and at the output of integrator 1 (TP13). It should now become a little clearer as to how the adaptive delta modulator is operating. It will be noted that the slope of the integrator's output signal is no longer constant, but increases in a series of discrete steps, in order to 'catch up' with the fast-changing analog input signal. If the integrator output does not 'catch up' with the analog input within two clock periods of its direction changing, the slope of the integrator's output signal. (i.e. the integrator gain) is doubled. If it has still not caught up with the
analog input signal by the end of the third clock period, the integrator gain will double once again. If the integrator output still lags behind at the end of the fourth clock period, the integrator's gain is doubled once again, to its maximum value. It then remains at this value until the integrator output 'catches up' with the analog input signal. Once the integrators output 'overtakes' the analog input
signal, its direction changes, and its rate of change reverts to the minimum value.
19. Examine also the test points in the adaptive control circuit 1 block (TP22-25), to have an understanding of how the adaptive delta modulator is operating.
20. While monitoring the outputs of the modulator's binary counter (TP22 and 23), slowly turn the 4 KHz preset anticlockwise, in order to reduce the amplitude of the 4 KHz analog input signal. Notice that once the analog input signal becomes small enough, both the counter's outputs becomes permanently low, causing the ST2155 integrator to have minimum gain. This happens because the input signal is now so small that the integrator can always follow it, even with minimum gain. The result is that small-amplitude input signals can be transmitted with minimum integrator gain, thereby keeping quantization noise to a minimum at the demodulator’s output.