This set of Analog Communications Multiple Choice Questions & Answers (MCQs) focuses on “Methods of Reducing Distortion”.
1. Quantization error occurs in ________
a) Time Division Multiplexing
b) Frequency Division Multiplexing
c) Pulse Code Modulation
d) Pulse Width Modulation
Explanation: The difference between an input value and its quantized value is called quantization error or we can also see it as that when an analog number is not converted into an exact digital number. It takes place in pulse code modulation (PCM). Pulse Code Modulation is a technique in which the amplitude of an analog signal is converted to a binary value represented as a series of pulses.
2. If power transmitted is 90kW, what is the field at a distance of 45km?
Explanation: Electric Field a region around a charged particle or object within which a force would be exerted on other charged particles or objects.
3. Find the number of pulses, if the number of quantization levels is 32 in PCM?
Explanation: Quantization is a process in which the continuous range of values of an analog signal is sampled and divided into non-overlapping (but not necessarily equal) subranges, and a discrete, unique value is assigned to each sub-range.
Therefore, number of pulse in quantisation level = 2n = 32, so n = 5, where n = Quantization Level.
4. Which transistor amplifier is most commonly used?
a) Common Base
b) Common Emitter
c) Common Collector
d) None of these
Explanation: Common Emitter is most widely used because it has high power gain and voltage gain. In this method of connection, small changes in base/emitter current cause large changes in collector/emitter current. Therefore, the circuit is that of a current amplifier. Moreover, it also provides maximum transconductance for a given load.
5. A device uses a 8 bit word then the maximum number of words it can transmit is ________
Explanation: Maximum number of words which an n-bit device can transmit = 2n
Therefore, when n = 8,
Number of words it can transmit is 28 = 256.
6. Peak voltage of a carrier is 8kV, each sideband has an amplitude of 800V. Find its modulation index?
Explanation: (mPc)/2 = Psb, where m = Modulation Index, Pc = Carrier Power and,
Psb = Power of each sideband
Therefore, (mVc 2)/2 = Vsb 22 (Vc = 8000 V, and Vsb = 800)
Therefore, m = (8002 X 2) / 80002 = 0.02.
7. What do you understand by the term Cross talk?
a) generation of closely lying sidebands
b) a method of increasing bandwidth
c) a method of decreasing bandwidth by converting DSB-SC signal to SSB-SC
d) disturbance caused in nearby circuit due to transmitted signal
Explanation: Crosstalk is a disturbance caused by the electric or magnetic fields of one telecommunication signal affecting a signal in an adjacent circuit. It is generally caused by undesired coupling. In a telephone circuit, crosstalk can result in the hearing part of a voice conversation from another circuit.
8. AM waves is represented by Et cos ωc t. What does Et denotes?
b) carrier signal
c) modulating signal
Explanation: AM wave is represented by (A + xt) cosωc t or Et cosωc t, where xt is modulating signal, A is amplitude and therefore, Et is the envelope of the AM wave.
9. Wireless communication takes place through ________
a) EM waves
c) Optical Fibres
d) Infrared Waves
Explanation: Wireless communication takes place through electromagnetic waves. Waves are transmitted through an antenna.
10. Which modulation technique uses minimum bandwidth?
Explanation: SSB-SC modulation technique uses minimum bandwidth as it suppresses the carrier and transmits either of the two side-bands while DSB-SC suppresses the carrier and transmits both the side-bands.
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