Roll No. …………………………………………………………
NEELKANTH INSTITUTE OF TECHNOLOGY
SECTION B
B.Tech ECE (Semester V)
Attempt any five parts of the following Questions: (10X5=50)
PRE-UNIVERSITY EXAMINATION 2015-2016
2. (a) Draw the circuit diagram of reactance modulator and explain its
principle of operation. Derive an expression for the equivalent
capacitance in terms of gm of the device and the circuit component.
(b) An angle modulated signal with carrier frequency 1MHz is
describe by the equation
𝜓𝐹𝑀 (𝑡) = 10cos⁡[𝑤𝑐 𝑡 + sin(3000𝑡) + 10 sin(2000𝜋𝑡)]
PRINCIPLE OF COMMUNICATION (NEC-502)
Time: 3 Hours
Total Marks 100
SECTION A
1. Attempt all the Questions:
(2X10=20)
(a) Write down the expression for spectral density of noise at the
output of the super heterodyne receiver if the DSB-SC is used.
(b) Define the selectivity, sensitivity and image frequency in a
radio receiver.
(c) What is pre-emphasis? Why it is used?
(d) Find transmission power efficiency for a tone modulated signal
when modulation index is 0.25.
(e) What is meant by “Threshold effect”?
(f) What is baseband and pass-band signal?
(g) A single tone modulated DSB signal has a peak envelope
voltage of 200V across a 50 ohm resistive load. Determine the
peak envelope power.
(h) The positive RF peaks of an AM Voltage rise to a maximum
value 12V and drop to minimum value of 4V. Find the
modulation index assuming single tone modulation.
(i) In an aerial Current (RMS) before modulation is 10A. After
modulating it to 11.6A. Determine the modulation Pmod. If the
carrier power is 10kW, what is the power after modulation?
(j) Write down the advantages of frequency translation/
Modulation.
i. Find the Power of the modulated signal
ii. Find the frequency deviation
iii. Estimate the bandwidth of the FM signals.
3. Draw explain the AM communication system transmitter & receiver
(super heterodyne). What do you mean by Figure of merit? Derive an
expression for figure of merit for DSB-SC system.
4. (a) What is the advantage of digital PLL? Explain the working of DFlip flop based digital phase detector.
(b) Discuss the multiplexing of PCM system. Describe the T1 digital
system in detail.
5. (a) What is delta modulation? Discuss the error in delta modulation.
How they are overcome in Adaptive delta modulation.
(b) For the given binary sequence construct the unipolar NRZ,
unipolar RZ, Bipolar NRZ, Bipolar RZ, Alternative mark inversion,
Manchester format. Also draw the Power spectral Density of all the
coding format.
6. (a) Explain the working of FM signal Modulator using indirect method
(Armstrong method) to obtained FM signal having carrier frequency
91.2 MHz. also show that weak signal interferences on carrier has
negligible effect on angle modulation system.
(b) With all the diagram explain the working of foster-seeley
discrimination method. Also draw the block diagram of balance
frequency discrimination.
(b) Explain the principle of VSB. Its advantage with all the equation.
(c) Explain working of Balance modulator with diagram and
required expression
7. (a) Derive a generalized equation for wideband and narrow band FM
in terms of modulation index.
(b) With the help of suitable diagram explain the working of
stereophonic broadcasting transmitter and receiver.
OR
(a) How pre-emphasis and de-emphasis used in Commercial FM
broadcasting. Derive an expression for SNR improvement
(b) What is Quadrature modulation? Write down its adavantages.
8. (a) Draw the block diagram of PCM 8 bit communication system.
Explain the working of Compander.
(b) Derive an expression for quantization error wit step size s.
9. Derive an expression for output SNR for square law AM demodulator.
OR
Derive an expression for output SNR in FM and compare with the
figure of merit FM & AM.
SECTION C
Attempt any two parts of the following Questions:
(15X 2=30)
10. (a) Design the AM Broadcast system using the given
specification in Figure 1. for receiver frequencies plan
including images (High side tuning and low side tuning
frequency)
Figure 1.
11. (a) Explain the generation of SSB-SC in contrast of Hilberttransform and also how it is demodulated.
(b) Differentiate between PAM, PWM, and PPM.
(c) In terms of sampling theorem how a PAM signal generated and
explain the detection process of PAM. Draw the block diagram of
generation of PWM. How a PPM signal generated from PWM.
12. (a) Discuss the classification, working advantage and
application of vocoder.
(b) Derive an expression for SNR in PCM system if the input
message signal is non periodic in nature.
(c) What is noise? Write down the sources of noise. Write down
the formula for noise bandwidth. Derive an expression for RC
circuit for output SNR.