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3, PULSE AMPLITUDE MODULATION & DEMODULATION
AIM:
To study and obtain pulse amplitude modulation and demodulation
APPARATUS REQUIRED
1. Transistor
2. AFO
3. IC NES66
4, Resistors
5, Capacitor
5.CRO
6. RPS ~
THEORY:
Pulse amplitude modulation is a scheme, which alters the amplitude of
regularly spaced rectangular pulses in accordance with the instantaneous values of @
continuous message signal.
Then amplitude of the modulated pulses represents the amplitude of the
intelligence.
‘A train of very short pulses of constant amplitude and fast repetition rate is
chosen the amplitude of these pulse is made to vary in accordance with that of a slower
modulating signal the result is that of multiplying the train by the modulating signal the
envelope of the pulse height corresponds to the modulating wave .the Pam wave contain
upper and lower side band frequencies -besides the modulating and pulse signals.
‘The demodulated PAM waves, the signal is passed through a low pass filter
having a cut -off frequencies equal to the highest frequency in the modulating signal. At
the output of the filter is available the modulating signal along with the DC component
PAM has the same signal to noise ratio as AM and so it is not employed in
practical circuits
PROCEDURE:
MODULATION 1. Make the cireuit as shown in circuit diagram fig A
Set the pulse generated’s output to be 4 vpp at 100HZ
Set AFO’s output at 2 vpp 100HZ.
Observe the output wave form on a CRO"
yReN
Tabulate the reading.
PAM MODULATION AND DEMODULATION
Be 10)
DORAN
ster.
Ze?
1
ae tog uTPUT To
RD
CARRIER
SIGNAL
e
Ra
| 2k
Px
6 cro
NAL a oo
001 pF PAM Waveform
DEMODULATION:
1, Connect the circuit as shown in fig (b)
2, Given the modulated output with AFO used to the input of the circuit.
3. Vary the potentiometer so that modulating signal is obtained,
4, Measure the amplitude of the signal and verify with that of the input, SAMPLE READING:
PAM
_ Modulating voltage Vm (V) Pulse Amplitude modulation (V)
4
SAMPLE READING:
DEMODULATION
Modulating voltage Vm (V) Pulse Amplitude demodulation (V)
RESULT:
‘The pulse amplitude modulation circuit is circuit assembled and studied and.
demodulated wave also done.
