Department of ECE
Question Bank EC304(Digital Communication)
6th Semester,Electronics&Communication Engineering
Chapter 1
Q1: A bandpass signal has a spectral range that extends from 20 to 82 kHz. Find the
acceptable range of the sampling frequency ƒs.
Q2: A bandpass signal has a center frequency ƒo and extends from ƒo5kHz to
ƒo+5kHz.The signal is sampled at a rate ƒs = 25khz.As the center frequency ƒo varies
from ƒo = 5khz to ƒo = 50khz.Find the ranges of ƒo for which the sampling rate is
adequate.
Q3: The signal v(t) = cos5pt+0.5cos10pt instantaneously sampled. The interval between
samples is Ts. Find the maximum allowable value for Ts.
Q4:The
bandpass
signal
v(t)=cos10wt+cos11wt+cos12wt
is
sampled
by
a
∞
impulse train
s(t)=
∑
∆
(
t kTs
).
−∞
(a) Find the maximum time between samples, Ts, to ensure reproduction without error.
(b) Using the result obtained in (a),obtain an expression for v s(t)=S(t)v(t).
Q5: The TDM system is used to multiplex the four signals
m
1
(t)= coswt,
m
2
(t)=0.5coswt,
m
3
(t)=2cos2wt and
m
4
(t)=cos4
w
0
t. If each signal is sampled at the same sampling rate
calculate the minimum sampling rate ƒs.
Q6: Three Signals
m
1
,
m
2
and
m
3
are to be multiplexed
m
1
and
m
2
have 5kHz bandwidth
and
m
3
has a 10 kHz bandwidth. Design a commutator switching system so that each
signal is sampled at its Nyquist rate.
Q7: The signal v(t)= cos8wt is sampled by using natural sampling . Determine the
minimum sampling rate ƒs.
Q8: Draw an AMI waveform corresponding to a binary bit stream 100110010101. The
polarity of the first pulse in the waveform may be set arbitrarily.
Q9: Write the nonlinear difference equation of the delta modulator. Let m(t) =
18x10³sin2pt and let the samples occur every 0.05 sec. starting at t=0.01 sec. The step
size is 5mV.
Q10: The input to DM is m(t) = 0.01t. The DM operates at a sampling frequency of
20Hz and has a step size of 2mV. Sketch the data modulator output , m (t) and m˜ (t).
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View Full DocumentQ11: The input to DM is m(t) = Kt. Prove by graphically determining m(t) = Kt.Prove,
by graphically determining m˜(t), that slope overload occurs when K exceeds a specified
value. What is the value in terms of the step size S and the sampling frequency ƒs?
Q12: Specify the Nyquist rate and the Nyquist interval for each of the following
signals:
(a) g(t) = sinc(200t)
(b) g(t) = sinc²(200t)
(c) g(t) = sinc(200t) + sinc²(200t).
Q13 Plot the spectrum of PAM wave produced by the modulating signal m(t) =A m
cos(2pƒmt) assuming a modulation frequency ƒm = 0.25Hz, sampling period Ts = 1s ,
and pulse duration T = 0.45s.
Q14 Twelve different message signal each with a bandwidth of 10 kHz, are to be
multiplexed and transmitted. Determine the minimum bandwidth required for each
method if the multiplexing/modulation method used is:
(a) FDM, SSB.
(b) TDM, PAM
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 Spring '11
 Dewey
 Bit rate, FSK signal

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