This set of Analog Communications Multiple Choice Questions & Answers (MCQs) focuses on “AM Wave Representation”.

1. AM waves is represented by which equation?

a) [1 + m(t)].c(t)

b) [1 – m(t)].c(t)

c) [1 + m(t)].2c(t)

d) [1 + 2m(t)].c(t)

View Answer

Explanation: Amplitude wave is represented by [1 + m(t)].c(t) where c(t) is carrier wave equal to ASin(2 π.fc.t) and m(t) is modulation waveform equal to M.Cos(2 π.fm.t + ∅).

2. For attenuation of high frequencies we can use ________

a) inductance

b) shunt capacitance

c) series capacitance

d) combination on inductor and resistor

View Answer

Explanation: Capacitive reactance, X_c is low for high frequencies. Due to this the high frequencies are shunted to ground and are not transmitted.

3. If each element of signal occupies 40ms, determine its speed?

a) 20 bauds

b) 25 bauds

c) 40 bauds

d) 0.05 bauds

View Answer

4. A modem is classified as low if speed of data rate is ________

a) upto 600bps

b) upto 200bps

c) upto 400bps

d) upto 500bps

View Answer

Explanation: Modem is device that can modulate carrier wave as well as demodulate signal to decode the transmitted information. When data rate in bps is upto 600, modem is considered having low speed.

5. Modulation is also called detection.

a) True

b) False

View Answer

Explanation: Modulation can be seen as the addition of information to a signal. Demodulation is technique to extract our original message signal back. Demodulation is also called detection.

6. It is suitable to connect woofer from the input through ________

a) band pass filter

b) band stop filter

c) low pass filter

d) high pass filter

View Answer

Explanation: Woofer is considered as a low frequency loud speaker. It has a range from 10Hz to 500Hz. So it is better to use low pass filter for connection.

7. The radiation at right angles is zero means ________

a) l = ʎ

b) l = ^{ʎ}⁄_{4}

c) l = 2 ʎ

d) l = ^{ʎ}⁄_{2}

where l = length of antenna and ʎ=wavelength.

View Answer

Explanation: Antenna is used for converting electromagnetic radiation into electric currents or vice-versa. If the length of antenna is equal to the whole wavelength then the radiation at right angles is zero.

8. Power of carrier wave is 500W and modulation index is 0.25. Find its total power?

a) 500W

b) 415W

c) 375W

d) 516W

View Answer

Explanation: Total power, P

_{t}= 500(1+

^{(0.25)2}⁄

_{2}) = 516W.

9. Commercial frequency deviation is ________

a) 75 KHz

b) 80 KHz

c) 85 KHz

d) 65 KHz

View Answer

Explanation: Commercial FM broadcasting uses a maximum deviation 75 KHz and maximum modulating frequency is approximately 15KHz.

10. Which of the following cannot be the Fourier series of a periodic signal?

a) x(t) = 2Cost + 4Cos7t

b) x(t) = 2Cosπt + 4Cos7t

c) x(t) = Cost + 0.7

d) x(t) = 2Cost + 4Sin7t

View Answer

Explanation: x(t) = Cost + 0.7 not follows dirchlet’s integral. Fourier series of a periodic signal must follow Dirichlet rule. Dirichlet integral states that a finite number should have finite number of discontinuities and also has finite number of extrema.

**Sanfoundry Global Education & Learning Series – Analog Communications.**

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