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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 4
1.
24 telephone channels, each band limited to 3.4 kHz are to be time division multiplexed using PCM. If sampling frequency is 10 kHz and number of quantization levels is 128, the required bandwidth of PCM is
1.68 MHz
240 kHz
81.6 kHz
3.072 MHz
Answer: Option
Explanation:

Bandwidth ≈ 24 (ln2 128) 10 kHz = 1.68 MHz.

2.
Resonant circuits are used in
audio amplifiers
RF amplifiers
both audio and RF amplifiers
none of the above
Answer: Option
Explanation:

RF amplifiers use resonant loads (L and C in parallel).

3.
The bandwidth of DSB suppressed carrier modulation system when the modulating frequency varies between 500 Hz and 5 kHz is
555 kHz
505 kHz
500 kHz
9 kHz
Answer: Option
Explanation:

fm = 5 kHz - 500 Hz 4.5 kHz

Bandwidth = 2 fm 2 x 4.5 kHz = 9 kHz.

4.
Linear diode detector utilizes
linear portion of static characteristics of diode
linear portion of dynamic characteristic of diode
square law portion of dynamic characteristics of diode
rectification property of diode
Answer: Option
Explanation:

Detection (also called demodulation) is due to rectification property of diode.

5.
In the equivalent circuit of a moving coil cone type loudspeaker, the mass of the moving system is represented by
a resistance
a capacitance
an inductance
a conductance
Answer: Option
Explanation:

Mass has inertia and is analogous to inductance.

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