EXPERIMENT:8

Aim: Perform adaptive delta modulation on matlab of given signal.

clc
clear all;

t =0:1/29:1;
f=1;
x=4*sin(2*pi*f*t);
x=[x ones(1,10) x];
y = zeros(1,length(x));
d = zeros(1,length(x));
e= zeros(1,length(x));
s=0.1;
for i=5:length(x)
if(x(i)-y(i-1))>=0
y(i) = x(i)-s;
d(i)=-1;
elseif(x(i)-y(i-1))<0
y(i)=x(i)-1;
d(i)=-1;
end

if(sum(d(i-4:i)))>3
s=s+0.01;
elseif(sum(d(i-4:i)))<-3
s=s+0.01;
elseif(sum(d(i-4:i)))==0
s=s-0.01;
else
s=s;
end
pause;
subplot 211; plot(x); hold on;
stem(y,'m');e=x-y;plot(e,'r');
title('Input,tracking and error graph');
subplot 212; stem (d,'k'); title('output data signal')
end
 EXPERIMENT:9

Amplitude Shift Keying (ASK)

Apparatus: ST2156 and ST2157 Trainers, 2 mm Banana cable, Oscilloscope Caddo 802 or
equivalent

Circuit Diagram:

Procedure:
1. Connect the power supplies of ST2156 and ST2157 but do not turn on the power supplies until
connections are made for this experiment.
2. Make the connections as shown in the figure.
3. Switch 'ON' the power.
4. On ST2156, connect oscilloscope CH1 to ‘Clock In’ and CH2 to ‘Data In’ and observe the
waveforms.
5. On ST2156, connect oscilloscope CH1 to ‘NRZ (L)’ and CH2 to ‘Output’ of modulator Circuit
(l) on ST2156 and observe the waveforms.
6. Vary the gain potentiometer of modulator circuit (l) on ST2156 to adjust the amplitude of ASK
Waveform.
7. On ST2156, connect oscilloscope CH1 to ‘NRZ (L)’ and CH2 to ‘Output’ of comparator on
ST2157 and observe the waveforms.
Observations:
1. The output at ‘Data In’ is repeating sequence of bits generated by Data Source.
2. The output at Modulator Circuit (l) is the ASK waveform which contains carrier transmitted for
Data ‘1’ and carrier suppressed Data ‘0’.
3. The output at comparator on ST2157 is the same as ‘Data In’ on ST2156.
Conclusion:

Remarks: Signature
 Frequency Shift Keying (FSK)
Aim: To study and observe Frequency Shift Keying modulation and
demodulation

Apparatus: ST2156 and ST2157 Trainers, 2 mm Banana cable, Oscilloscope Caddo 802 or
equivalent

Circuit Diagram:

Procedure:
1. Connect the power supplies of ST2156 and ST2157 but do not turn on the power supplies until
connections are made for this experiment.
2. Make the connections as shown in the figure 3.1.
3. Switch 'ON' the power.
4. On ST2156, connect oscilloscope CH1 to ‘Clock In’ and CH2 to ‘Data In’ and observe the
waveforms.
5. On ST2156, connect oscilloscope CH1 to ‘NRZ (L)’ and CH2 to ‘Output’ of Summing
Amplifier on ST2156 and observe the waveforms.
6. Adjust the potentiometers of both the Modulator Circuit (l) &(ll) onST2156 to adjust the
amplitude of FSK waveform at Summing Amplifier’s output on ST2156.
7. On ST2156, connect oscilloscope CH1 to ‘NRZ (L)’ and CH2 to ‘Output’ of comparator on
ST2157 and observe the waveforms.

Observations:
1. The output at Summer Amplifier is the FSK waveform, Observe that for data bit '0' the FSK
signal is at lower frequency (960KHz) & for data bit '1’ the FSK signal is at higher frequency (1.6
MHz)The output at comparator on ST2157 is the same as ‘Data In’ on ST2156.
Conclusion:

Remarks: Signature
 Phase Shift Keying (PSK)
Aim: To study and observe Phase Shift Keying modulation and demodulation

Apparatus: ST2156 and ST2157 Trainers, 2 mm Banana cable, Oscilloscope Caddo 802 or
equivalent

Circuit Diagram:

Procedure:
1. Connect the power supplies of ST2156 and ST2157 but do not turn on the power supplies until
connections are made for this experiment.
2. Make the connections as shown in the figure 4.1.
3. Switch 'ON' the power.
4. On ST2156, connect oscilloscope CH1 to ‘Clock In’ and CH2 to ‘Data In’ and observe the
waveforms.
5. On ST2156, connect oscilloscope CH1 to ‘NRZ (L)’ and CH2 to ‘Output’ of Modulator Circuit
(l) on ST2156 and observe the waveforms.
6. Adjust the ‘Gain’ potentiometer of the Modulator Circuit (l) on ST2156 to adjust the amplitude
of PSK waveform at output of Modulator Circuit (l) on ST2156.
7. Now on ST2157 connect oscilloscope CH1 to ‘Input’ of PSK demodulator and connect CH2
one by one to output of double squaring circuit, output of PLL, output of Divide by four (÷ 2)
observe the wave forms.
8. On ST2157 connect oscilloscope CH1 to output of Phase adjust and CH2 to ‘output’ of PSK
demodulator and observe the waveforms. Set all toggle switch to 0 and compare the waveform
now vary the phase adjust potentiometer and observe its effects on the demodulated signal
waveform. (Note: If there is problem in setting the waveform with potentiometer then toggle
the switch given in PSK demodulator block two to three times to get the required waveform).
9. Now connect oscilloscope CH1 to ‘PSK’ output of PSK demodulator on ST2157 and connect
CH2 ‘Output’ of Low Pass Filter on ST2157 and observe the waveforms.
10. Connect oscilloscope CH1 to ‘Output’ of Low Pass Filter on ST2157 then connect CH2 to
‘Output’ of Comparator on ST2157 and observe the waveforms, now vary the reference voltage
potentiometer of first comparator to generate desired data pattern.
11. On ST2156, connect oscilloscope CH1 to ‘NRZ (L)’ and CH2 to ‘Output’ of comparator on
ST2157 and observe the waveforms.
12. Connect oscilloscope CH1 to ‘Data In’ then connect CH2 output to Bit decoder and observe
the waveforms. If both data does not matches then try to match it by varying the phase adjust
potentiometer on QPSK Demodulator.
13. Now try to match the LED sequence by once pressing the reset switch on ST2156.

Observations:
1. The output at ‘Data In’ is repeating sequence of bits generated by Data Source.
2. The ‘Output’ of Modulator Circuit (l) is Phase Shift Keying modulated signal.
3. The output of Double squaring circuit is sinusoidal signal (carrier signal) but frequency is four
times higher than that of carrier used for modulation.
4. The output of Phase Lock Loop (PLL) is clock signal of same frequency as that of the output of
double squaring circuit and output of Divide by two (÷ 2) is clock signal of frequency two times
less than the output of PLL signal.
5. The output of PSK demodulator is a signal having group of positive half cycles and group of
negative half cycles of the carrier signal.
6. A low pass filter removes high frequency component from demodulated PSK signal and it makes
the signal smooth.
7. The variation in reference voltage potentiometer affect the Data, to recover Data correctly
potentiometer adjustment is necessary.
8. The Phase Adjust potentiometer on ST2157 matches the phase of regenerated clock and carrier
with input clock and carrier signal.

Conclusion:

Remarks: Signature
 EXPERIMENT:9
Aim: Perform ASK FSK and PSK on matlab of given signal.

Code:
%matlab code for digital modulation(ask, fsk and psk)
f=5;
f2=10;
x=[1 1 0 0 1 0 1 0] % input signal ;
nx=size(x,2);

i=1;
while i<nx+1
t = i:0.001:i+1;
if x(i)==1
ask=sin(2*pi*f*t);%ask
fsk=sin(2*pi*f*t); %fsk
psk=sin(2*pi*f*t); %psk
else
ask=0;
fsk=sin(2*pi*f2*t);
psk=sin(2*pi*f*t+pi);
end
subplot(3,1,1);
plot(t,ask);
hold on;
grid on;
axis([1 10 -1 1]);
title('Amplitude Shift Key')
subplot(3,1,2);
plot(t,fsk);
hold on;
grid on;
axis([1 10 -1 1]);
title('Frequency Shift Key')

subplot(3,1,3);
plot(t,psk);
 hold on;
grid on;
axis([1 10 -1 1]);
title('Phase Shift Key')

i=i+1;
end