9028062.doc

9028062.doc - Exp.No:01 PHASE SHIFT KEYING AIM Study the...

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Exp.No:01 PHASE SHIFT KEYING AIM: Study the operation of PSK (Binary) Modulation & Demodulation and to plot the PSK wave forms for Binary data at different frequencies. APPARATURS: 1. Phase Shift Keying trainer 2. Dual trace Oscilloscope 3. Digital multi meter 4. Patch chords BLOCK DIAGRAM: 1
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Fig.1.1 PSK Demodulator Fig.1.2 PSK Demodulator THEORY: 2
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Phase Shifting Keying (PSK) is a modulating / Data transmitting technique in which phase of the carrier signal is shifted between two distinct levels. In a simple PSK (i.e. Binary PSK) un shifted carrier Vcos W t is transmitted to indicate a 1 condition, and the carrier shifted by 180º i.e-Vcos ˳ W t is transmitted to indicate a 0 condition. Wave forms are shown in Figure PSK Modulating & ˳ Demodulating circuitry can be developed in number of ways, one of the simple circuit is used in this trainer. PROCEDURE: 1. Study the THEORY of operation. 2. Connect the trainer to mains and switch on the power supply. 3. Measure the output of the regulated power supply ie. +5V and -5V with the help of digital multimeter. 4. Observe the output of the carrier generator using CRO, it should be an 8 KHz Since with 5 Vpp amplitude. 5. Observe the various data signals (1KHz, 2KHz and 4KHz) using CRO. Modulation: 6. Connect carrier signal to carrier input of the PSK Modulator. 7. Connect data signal say 4 KHz from data source to data input of the modulator. 8. Keep CRO in dual mode. 9. Connect CH1 input of the CRO to data signal and CH2 to the output of the PSK modulator 10. Observe the PSK o/p signal with respect to data signal and plot the wave forms Compare the plotted waveforms with given wave forms. Demodulation: 11. Connect the PSK output the PSK input of the demodulator. 12. Connect carrier to the carrier input of the PSK demodulator Note: In actual communication system reference carrier is generated at receiver. 13. Keep CRO in dual mode. 14. Connect CH1 to the data signal (at Modulator) and CH2 to the output of the demodulator. 3
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15. Compare the demodulated signal with original data signal, By this we can notice that there is no loss in modulation and demodulation process. 16. Repeat the steps 7 to 15 with different data signals i.e 2KHz and 1KHz. Figure 1.3 PSK wave forms for different data input signals 4
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Exp.No:02 DIFFERENTIAL PHASE SHIFT KEYING AIM: Study the characteristics of differential phase shift keying APPARATUS: 1. Differential Phase Shift Keying Kits. 2. CRO (20MHz). 3. Digital multimeter. 4. No’s of coaxial cables (standard accessories with trainer). BLOCK DIAGRAM: 5
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Fig. 2.1 DPSK Modulator 6
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Fig. 2.2 DPSK Demodulator THEORY: DPSK: Phase Shift Keying requires a local oscillator at the receiver which is accurately synchronized in phase with the un-modulated transmitted carrier, and in practice this can be difficult to achieve. Differential Phase Shift Keying (DPSK) over comes the difficult 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. In other words DPSK is a noncoherent version of the PSK.
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