AIM: To study the operation of FSK modulation and de modulation and to plot the graph.
APPARATUS:
1. Frequency shift keying system
2. Dual trace oscilloscope
3. Connecting wires
4. Dual multi meter
5 .Digital frequency counter
THEORY:
In FSK system two sinusoidal carrier waves of the same amplitude Ac but different frequencies fc1 and fc2 are used represent binary symbols ‘1’ and ‘0’ respectively .The Binary FSK wave S(t) may be represented as
S (t) = Ac cos (2Πfc1T) for ‘1’
= Ac cos (2Πfc2T) for ‘0’
The binary FSK wave form is illustrated in figure for the arbitory sequence .It can be easily verified that binary FSK wave form is essentially a super position of two binary ASK wave forms, one with a frequency fc1.
PROCEDURE:
1. Connect the trainer to mains and switch on the power supply.
2. Measure the o/p voltage of the RPS i.e., +12V with the help of digital multimeter
3. Verify the operation of the logic source using ‘0’ Position and 12V in logic ‘1’ position
4. Observe the o/p of the data signal using oscilloscope it should be a Square wave of 20Hz to 180Hz at 10Vp-p
FOR MODULATION:
5. Connect the out put of the logic source to data p/p of the FSK modulator.
6. Set the logic source switch in ‘0’ position.
7. Connect the FSK modulator out put to CRO as well as frequency counter CRO.
8. Set the o/p frequency of the FSK modulator per your desire with the help of control to which represents logic ‘0’.
9. Set the logic ‘0’ switch in ‘1’ position.
10. As per your desire with the help of control F, which represents logic ‘1’.
11. Now connect the data p/p of the FSK modulator to the o/p of the data signal generator.
12. Keep CRO in dual trace mode, connect with c1+1, i/p of the FSK modulator.
13. Observe the FSK signal for different data signal frequencies and plot them by this. We can observe that the carrier frequency is shifting bin two pre determined frequencies at the data signal i.e., 1 KHz when data signal is zero and 2.4 KHz when data output is ‘1’ in its case and the other with frequency fc2. Hence the Power density spectrum of FSK is the sums of two ASK spectra at frequencies fc1 and other frequency fc2. Hence the power density spectrums of FSK signal.
It may be noted that the bandwidth of FSK is higher than that of ASK (or) PSK, the spectrum of FSK signal. FSK signaling scheme find a wide range of applications for low-speed digital data transmission.
14. Compare these plotted waveforms with theoretically.
For Demodulation:
15. Again connect the i/p of the FSK modulator to the help of to control.
16. Now put data source switch in ‘1’ position and set the FSK o/p frequency to 2225 Hz with the help of F1 control without disturb the F0.
17. Disconnect the FSK i/p of the modulator from logic source and connect data signal generator.
18. Now put data source switch in’1’ position and set the FSK o/p frequency to 2225 Hz with the help of F1 control without disturbing the F0.
19. Disconnect the FSK i/p of the modulator from logic source and connect the data generator.
20. Observe the o/p of the modulator using CRO &compare them with the given wave forms.
21. Now connect the FSK modulator o/p to the FSK i/p of the demodulator.
22. Connect CH-1 i/p of the CRO to the data signal at modulator and CH-2 i/p of the o/p of the FSK modulator.
23. Observe the o/p and plot the o/p of the FSK demodulator compare the original data signal and demodulated signal by this we observe that there is no demodulated signal in FSK modulation.
PRECATIONS:
1. Connections are made without loose connections.
2. Readings are taken without parallax error.
3. Plot the graph care fully.
RESULT
APPARATUS:
1. Frequency shift keying system
2. Dual trace oscilloscope
3. Connecting wires
4. Dual multi meter
5 .Digital frequency counter
THEORY:
In FSK system two sinusoidal carrier waves of the same amplitude Ac but different frequencies fc1 and fc2 are used represent binary symbols ‘1’ and ‘0’ respectively .The Binary FSK wave S(t) may be represented as
S (t) = Ac cos (2Πfc1T) for ‘1’
= Ac cos (2Πfc2T) for ‘0’
The binary FSK wave form is illustrated in figure for the arbitory sequence .It can be easily verified that binary FSK wave form is essentially a super position of two binary ASK wave forms, one with a frequency fc1.
PROCEDURE:
1. Connect the trainer to mains and switch on the power supply.
2. Measure the o/p voltage of the RPS i.e., +12V with the help of digital multimeter
3. Verify the operation of the logic source using ‘0’ Position and 12V in logic ‘1’ position
4. Observe the o/p of the data signal using oscilloscope it should be a Square wave of 20Hz to 180Hz at 10Vp-p
FOR MODULATION:
5. Connect the out put of the logic source to data p/p of the FSK modulator.
6. Set the logic source switch in ‘0’ position.
7. Connect the FSK modulator out put to CRO as well as frequency counter CRO.
8. Set the o/p frequency of the FSK modulator per your desire with the help of control to which represents logic ‘0’.
9. Set the logic ‘0’ switch in ‘1’ position.
10. As per your desire with the help of control F, which represents logic ‘1’.
11. Now connect the data p/p of the FSK modulator to the o/p of the data signal generator.
12. Keep CRO in dual trace mode, connect with c1+1, i/p of the FSK modulator.
13. Observe the FSK signal for different data signal frequencies and plot them by this. We can observe that the carrier frequency is shifting bin two pre determined frequencies at the data signal i.e., 1 KHz when data signal is zero and 2.4 KHz when data output is ‘1’ in its case and the other with frequency fc2. Hence the Power density spectrum of FSK is the sums of two ASK spectra at frequencies fc1 and other frequency fc2. Hence the power density spectrums of FSK signal.
It may be noted that the bandwidth of FSK is higher than that of ASK (or) PSK, the spectrum of FSK signal. FSK signaling scheme find a wide range of applications for low-speed digital data transmission.
14. Compare these plotted waveforms with theoretically.
For Demodulation:
15. Again connect the i/p of the FSK modulator to the help of to control.
16. Now put data source switch in ‘1’ position and set the FSK o/p frequency to 2225 Hz with the help of F1 control without disturb the F0.
17. Disconnect the FSK i/p of the modulator from logic source and connect data signal generator.
18. Now put data source switch in’1’ position and set the FSK o/p frequency to 2225 Hz with the help of F1 control without disturbing the F0.
19. Disconnect the FSK i/p of the modulator from logic source and connect the data generator.
20. Observe the o/p of the modulator using CRO &compare them with the given wave forms.
21. Now connect the FSK modulator o/p to the FSK i/p of the demodulator.
22. Connect CH-1 i/p of the CRO to the data signal at modulator and CH-2 i/p of the o/p of the FSK modulator.
23. Observe the o/p and plot the o/p of the FSK demodulator compare the original data signal and demodulated signal by this we observe that there is no demodulated signal in FSK modulation.
PRECATIONS:
1. Connections are made without loose connections.
2. Readings are taken without parallax error.
3. Plot the graph care fully.
RESULT
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