Communication Systems - Study Mode

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[#76] Boosting of higher frequency at the transmitter is done by using

(A) De-emphasis

(B) AGC circuit

(C) Pre-emphasis

(D) Armstrong method

Correct Answer

(C) Pre-emphasis

[#77] A signal contains components at 400 Hz and 2400 Hz. This signal modulates a carrier of frequency 100 MHz. However after demodulation it is found that the 400 Hz signal component is present. The channel Bandwidth is 15 KHz. What is the reason for the higher frequency signal not to be detected properly.

(A) Modulation used in FM and BW

(B) Modulation used in AM and BW is insufficient

(C) Modulation used in FM but pre emphasis is not used

(D) Modulation used in AM but detector is for FM

Correct Answer

(C) Modulation used in FM but pre emphasis is not used

[#78] Match List-I with List-II and select the correct answer using the options given below: List-I List-II a. SSB 1. Envelope detector b. AM 2. Integrate and dump c. BPSK 3. Hilbert transform

(A) a-3, b-1, c-2

(B) a-3, b-2, c-1

(C) a-2, b-3, c-1

(D) a-1, b-2, c-3

Correct Answer

(A) a-3, b-1, c-2

[#79] Consider the frequency modulated signal 10cos[2π × 10 t + 5sin(2π + 1500t) + 7.5sin(2π × 1000t)] with carrier frequency of 10 5 Hz. The modulation index is

(A) 12.5

(B) 10

(C) 7.5

(D) 5

Correct Answer

(B) 10

[#80] For a frequency-modulated signal, the modulation index is doubled. The average power of the modulated signal is

(A) quadrupled

(B) doubled

(C) unaltered

(D) none of these

Correct Answer

(C) unaltered