STUPIDSID
1 (a)
Draw the general block diagram of a communication system and briefly explain
the function of each block.
7 M
1 (b)
Define equivalent noise temperature.
A receiver is connected to an antenna whose resistance is 50 Ω has an
equivalent noise resistance of 30Ω Calculate the receiver's noise figure in
decibels and its equivalent noise temperature.
7 M
2 (a)
Give complete classification of noise. Explain the effect of reactive elements on
noise contribution.
7 M
2 (b)
In a broadcast super heterodyne receiver having no RF amplifier, the loaded Q
of the antenna coupling circuit at the input to the mixer is 100. If the
intermediate frequency is 455 kHz, calculate (1) the image frequency and its
rejection ratio at 1000 kHz and (2) the image frequency and its rejection ratio at
25 Mhz.
7 M
2 (c)
The first stage of a two-stage amplifier has a voltage gain of 10, a 600 ? input
resistor, a 1600Ω equivalent noise resistance and a 27 kΩ output resistor. For
the second stage, these values are 25, 81 kΩ, 10 kΩ and 1MΩ respectively.
Calculate the equivalent input-noise resistance of this two-stage amplifier. Also,
calculate the noise figure of this amplifier if it is driven by a generator whose
output impedance is 50Ω..
7 M
3 (a)
An AM signal is represented by
e(t) = (20+4 sin 500πt) sin (2π ×106t)
Find: Modulation index, total power and transmission Bandwidth required for this AM signal.
e(t) = (20+4 sin 500πt) sin (2π ×106t)
Find: Modulation index, total power and transmission Bandwidth required for this AM signal.
7 M
3 (b)
Explain the demodulation process of an SSB-SC signal with relevant
mathematical expressions.
7 M
3 (c)
A DSB-SC transmitter radiates 1 kW when modulation depth is 60%. How
much of carrier power is required in kW, if we want to transmit the same
message by an AM transmitter? What is the change required in transmission
Bandwidth?
7 M
3 (d)
The antenna current of an AM transmitter is 8 A for an unmodulated carrier but
it increases to 8.93 A when the carrier is modulated by a single sine wave. Find
the percentage modulation. Determine the antenna current when the percentage
modulation changes to 0.8.
7 M
4 (a)
An FM signal is given by s(t) =10 cos (2 π ×106t+5 sin (2000πt)). Find the
total power and bandwidth required to transmit this FM signal.
7 M
4 (b)
A super heterodyne receiver is to operate in the range of 550 kHz- 1650 kHz,
with intermediate frequency of 450 kHz. Determine the required capacitance ratio of the local oscillator. Also find image frequency when this receiver is
tuned to 700 kHz.
7 M
4 (c)
Define the following terms related with radio receivers:
(1) Selectivity (2) Fidelity (3) sensitivity (4) Tracking (5) AGC (6) Adjacent channel selectivity (7) Double spotting
(1) Selectivity (2) Fidelity (3) sensitivity (4) Tracking (5) AGC (6) Adjacent channel selectivity (7) Double spotting
7 M
4 (d)
Compare the performance of a ratio detector with a Foster-Seeley discriminator.
7 M
5 (a)
In a series RLC circuit R=10Ω, L= 100 mH and C= 47 μF. Determine 3-dB
bandwidth of this circuit.
7 M
5 (b)
Determine Fourier Transform of a Rectangular (Gate) Function.
7 M
5 (c)
State and prove convolution property.
7 M
5 (d)
Compare AM and FM.
7 M
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