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Digital modulation

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EIE 312
Electronics Engineering Laboratory
Experiment: Digital Modulation and Demodulation
1: Curriculum Objectives
1. To understand the Amplitude Shift Keying (ASK) signal.
2. To understand the Frequency Shift Keying (FSK) signal.
3. To understand the Phase Shift Keying (PSK) signal.
4. To implement Digital Receiver
2: Curriculum Theory
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EIE 312
Electronics Engineering Laboratory
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EIE 312
Electronics Engineering Laboratory
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EIE 312
Electronics Engineering Laboratory
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EIE 312
Electronics Engineering Laboratory
3 Experimental Procedures
Experiment 1: ASK modulator
1. Turn on function waveform generator RIGOL DG1062
2. Set CH1 to Sine waveform with frequency 100kHZ by choosing
“Freq” on screen menu and input 100KHz.
3. Press Mod button to get modulated signal and choose “Type” on
screen menu and then choose “AM”.
4. Press “AM Freq” on screen menu and input 1kHZ and select “AM
Depth” and input 100%
5. Press “Shape” on screen menu and choose square.
6. Connect output CH1 OOK signal to Oscilloscope and record the result
signal in Table 1.
7. Press “Type” on screen menu and choose ASK
8. Press “ASK Rate” on screen menu and choose 1kHz.
9. Press “ASK Amp” on screen menu and choose 1 Vp-p.
10. Connect output CH1 to Oscilloscope and record the result signal in
Table 2.
11. Use AM Demodulator Diode detection AM circuit to demodulate
signal from CH1.
12. By using oscilloscope, observe AM I/P, TP1, TP2, TP3, TP4 and
Audio O/P signal waveforms. Then record the measured results in
table 3.
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EIE 312
Electronics Engineering Laboratory
Experiment 2: FSK modulator
1. Turn on function waveform generator RIGOL DG1062
2. Set CH1 to Square waveform with frequency 20kHZ by choosing
“Freq” on screen menu and input 20KHz.
3. Press Mod button to get modulated signal and choose “Type” on
screen menu and then choose “FM”.
4. Press “FM Freq” on screen menu and input 1kHZ and select “FM
Dev” and input 2kHz.
5. Connect output CH1 to Oscilloscope and record the result signal in
Table 4.
6. Press “Type” on screen menu and choose FSK
7. Press “FSK Rate” on screen menu and choose 1kHz.
8. Press “HOP Freq” on screen menu and choose 1kHz.
9. Connect output CH1 to Oscilloscope and record the result signal in
Table 5.
10. Use CD4046 FM Demodulation circuit to demodulate signal from
CH1.
11. Set TP1 on Demodulation circuit to 20kHz.
12. By using oscilloscope, observe FM I/P, TP2, and Audio O/P signal
waveforms. Then record the measured results in table 6.
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EIE 312
Electronics Engineering Laboratory
Experiment 3: PSK modulator
1. Turn on function waveform generator RIGOL DG1062
2. Set CH1 to Sine waveform with frequency 100kHZ by choosing
“Freq” on screen menu and input 100KHz.
3. Press Mod button to get modulated signal and choose “Type” on
screen menu and then choose “PSK”.
4. Press “PSK Rate” on screen menu and input 1kHZ and select “FM
Dev” and input 1kHz.
5. Connect output CH1 to Oscilloscope and record the result signal in
Table 7.
6. Use AM Demodulator Product detection AM circuit to demodulate
signal from CH1.
7. By using oscilloscope, observe AM I/P, TP1, TP2, TP3, TP4, TP5,
TP6, TP7 and Audio O/P signal waveforms. Then record the measured
results in table 8.
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EIE 312
Electronics Engineering Laboratory
4: Measured Results
Table 1 Measured results of OOK signal.
OOK
Table 2 Measured results of ASK signal.
ASK
Table 3 ASK Demodulation
Output Ports
AM I/P
TP1
TP2
TP3
TP4
Audio O/P
Signal Picture
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EIE 312
Electronics Engineering Laboratory
Table 4 Measured results of FM with square audio signal.
FM
Table 5 Measured results of FSK signal.
FSK
Table 6 FSK Demodulation
Output Port
Signal Picture
FM I/P
TP2
LPF IN
Audio O/P
Table 7 Measured results of PSK signal.
PSK
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EIE 312
Electronics Engineering Laboratory
Table 8 PSK Demodulation
Output Port
Signal Picture
AM I/P
TP1
TP2
TP3
TP4
TP5
TP6
TP7
Audio O/P
5: Discussion Questions
1. Describe the different between OOK and ASK.
2. Explain why OOK and ASK can be demodulated with diode detector.
3. Describe the different between FM with square audio input and FSK.
4. Explain how FSK can be demodulated with FM detector.
5. Explain why PSK can be demodulated with AM product detection circuit.
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