# Analog Communications Questions and Answers – Detection of AM Waves

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

1. Detection is same as ________
a) Modulation
b) Mixing
c) Filtering
d) Demodulation

Explanation: Process of extracting the original message signal from the received modulated signal is called demodulation. Demodulation is also known as detection.

2. Most commonly used modulation system for telegraphy is ________
a) Multi-tone modulation
b) Single tone modulation
c) PCM
d) FSK

Explanation: FSK (Frequency Shift Keying) is a method to transmit digital signals, which are in form of binary data. In telegraphy, a modem is used to convert binary data to FSK and vice-versa, for communication between computers, over telephone lines. Single tone modulations deals with message signal having single frequency component, whereas, Multi-tone modulation deals with message signal having multiple frequency components.

3. What do you understand by the term “carrier”?
a) waveform with constant frequency, phase and amplitude
b) waveform for which frequency, amplitude or phase is varied
c) waveform with high amplitude, low frequency and constant phase
d) waveform to be transmitted

Explanation: A carrier wave is modulated in terms of amplitude, frequency or phase, with respect to an input signal for conveying information. Carrier wave has generally higher frequency than the input signal.
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4. According to Fourier analysis, square wave can be represented as ________
a) fundamental sine wave and even harmonics
b) fundamental sine wave and odd harmonics
c) fundamental sine wave and harmonics
d) fundamental and sub harmonic sine wave

Explanation: A square wave is a non-sinusoidal periodic waveform with steady frequency, in which the amplitude alternates between a fixed maximum and minimum value. According to Fourier analysis, an ideal square wave, with amplitude one, can be represented as an infinite sum of sinusoidal waves. An ideal square wave contains only components of odd integer harmonics.

5. PDM is generated by ________
a) Bistable multivibrator
b) Monostable multivibrator
c) Astable multivibrator
d) Schmitt trigger

Explanation: PDM (Pulse Duration Modulation) is used to produce an analog signal with the help of a digital source. Monostable multivibrators are used to generate a single output pulse of a particular width. Its output is either high or low when a suitable external pulse is applied.
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6. Mass of any moving system is represented by ________
a) a resistance
b) a conductance
c) a resistivity
d) an inductance

Explanation: Inductance can also be seen as electromagnetic inertia, a property that opposes changes in electric currents and magnetic fields. Mass has inertia so it is represented by an inductance.

7. Contrast function in TV is done by ________
a) Luminance amplifier
b) Schmitt trigger
c) Band Pass Filter
d) Chroma amplifier

Explanation: Luminance amplifier is mostly used by the Contrast Function, in TV sets. It helps to changes the contrast or picture quality of television with respect to the received visual signals, by making the contrast optimum.

8. Bandwidth of RF amplifier for a color TV receiver is ________
a) equal to channel width
b) more than channel width
c) less than channel width
d) twice of channel width

Explanation: RF amplifiers are tuned amplifiers in which the frequency of operation is controlled by a tuned circuit. Bandwidth of RF amplifier is generally kept a little more than channel so that there is no problem in reception.

9. FSK system involves ________
a) frequency modulation
b) pulse modulation
c) amplitude modulation
d) phase modulation

Explanation: FSK (Frequency Shift Keying) is a method to transmit digital signals, which are in form of binary data. FSK i.e. Frequency Shift Keying involves frequency modulation that assigns bit values to discrete frequency while ASK assigns bit values to discrete amplitude.

10. Diameter of antenna is doubled. The maximum range will ________
a) be doubled
b) be halved
c) become four times
d) decrease to one fourth

Explanation: Range of antenna is directly proportional to antenna diameter. So if diameter of antenna is doubled its range also doubled.

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