This set of Analog Communications Multiple Choice Questions & Answers (MCQs) focuses on “Generation of AM Waves”.
1. Which of the following devices is used to generate AM waves?
a) Square-law modulator
Explanation: AM signals is generated by Square-law modulators. The input for generating AM signal should be of type (A + m(t)) instead of m(t). Square-law modulator sums carrier and information signal, then square them using a non linear device.
2. What is the disadvantage of FM over AM ?
a) high modulating power is needed
b) requires high output power
c) large bandwidth required
d) high noise is produced
Explanation: Advantage of FM over AM is that the amplitude of an FM wave remains constant. In FM, power of transmitted wave depends on amplitude of unmodulated carrier wave and hence it is constant.
3. For low level amplitude modulation, amplifier must be ________
b) non linear
d) class A amplifier
Explanation: Low level AM transmitter is same as high level transmitter except that power of carrier are not amplified. The signals are directly applied to the class C power amplifier.
4. Approximate range of a cordless telephone is ________
Explanation: Cordless telephone is that in which the handset is portable and communicates with the body of the phone by radio waves instead of being attached by a cord. Basically length depends on quality of instrument and is about 90m to 100m.
5. A wave is modulated by two sin waves having modulation indices of 0.3 and 0.5. Find the total modulation index?
Explanation: Given that m1 = 0.3 and m2 = 0.5. Total modulation index will be equal to . By substituting values we have which is equal to 0.58.
6. Carrier wave carries information.
Explanation: It is a high frequency electro-magnetic wave. A carrier wave does not have any information. It is modulated with an input signal for the purpose of conveying information.
7. What can we do to eliminate distortion in the picture?
a) use a longer transmission line
b) change the antenna orientation
c) twist the transmission line
d) connect a booster
Explanation: According to modulation, length of antenna should be one fourth of wavelength. If distortion occurs whether in television or at any other place, simplest way to eliminate this is to change the orientation of antenna.
8. For 100% amplitude modulation, the power in upper sideband when carrier power is to be 100W?
Explanation: Modulation index, m = 100% = 1. Power in sidebands is (Pcx m2⁄4) . By substituting the values, we have (100 x 1⁄4) which is equal to 25W.
9. Modem is considered as high speed if data rate is ________
Explanation: For data rate in the range 2000 to 10500 bps, modem is designated as high speed. Modem is combination of modulator and demodulator.
10. Scanning always takes place from ________
a) right to left
b) left to right
c) left to right for odd fields and right to left for even fields
d) left to right for even fields and right to left for odd fields
Explanation: Scanning is mostly used in TV to obtain continuous frames and to provide motion of picture. Scanning is always take place from left to right.
Sanfoundry Global Education & Learning Series – Analog Communications.
To practice all areas of Analog Communications, here is complete set of 1000+ Multiple Choice Questions and Answers.