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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 6
16.
A sinusoidal signal with peak to peak amplitude of 1.536 volt is quantized into 128 levels using a mid-rise uniform quantizer. The quantization noise power is
0.768 V
48 x 10-6 V
12 x 10-6 V
3.072 Volt
Answer: Option
Explanation:

.

17.
An FM wave is made to pass through a frequency tripler. If original modulation index is mf, the output of tripler has a modulation index equal to
mf
mf
3 mf
mf
Answer: Option
Explanation:

Frequency tripler makes modulation index three times.

18.
A balun provides an impedance transformation of
16 : 1
8 : 1
4 : 1
2 : 1
Answer: Option
Explanation:

Balun has turn ratio of 2 : 1. Therefore, impedance transformation is 4 : 1.

19.
A signal m(t) with bandwidth 500 Hz is first multiplied by a signal g(t) where . The resulting signal is then passes through an ideal low pass filter with bandwidth 1 kHz the output of the low pass filter would be
δ(t)
m(t)
0
m(t) δ(t)
Answer: Option
Explanation:

Multiplication in time domain is equivalent to convolution. According to the property of impulse signal, convolution of a signal m(t) with δ(t) is signal itself.

m(t) x g(t)

m(t).

20.
If γ = (S0/N0)/(Si/Nm) where S0 and S1 are signal power output and signal power input and N0 and Nm are noise power output and noise power input, the value of γ for SSB-SC and DSB-SC amplitude modulated system respectively are
1 and 1
1 and 2
2 and 1
0.5 and 0.5
Answer: Option
Explanation:

SSB - SC and SSB - DB have γ = 1 and are similar from noise point.

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