Experiment: Digital Modulation and Demodulation

Transcription

1 1 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

2 2

3 3

4 4

5 3 Experimental Procedures 5 Experiment 1: ASK modulator 1. Turn on function waveform generator RIGOL DG 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 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 Use AM Demodulator Diode detection AM circuit to demodulate signal from CH 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.

6 6 Experiment 2: FSK modulator 1. Turn on function waveform generator RIGOL DG 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 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 Use CD4046 FM Demodulation circuit to demodulate signal from CH 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.

7 7 Experiment 3: PSK modulator 1. Turn on function waveform generator RIGOL DG 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 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.

8 8 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 Signal Picture AM I/P TP1 TP2 TP3 TP4 Audio O/P

9 9 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

10 Table 8 PSK Demodulation EIE 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.