This set of Analog Communications Multiple Choice Questions & Answers (MCQs) focuses on “Spectrum of Multitone Signal”.
1. Video signals are transmitted through ________
a) Frequency Modulation
b) Amplitude Modulation
c) Pulse Modulation
d) Either frequency or amplitude modulation
Explanation: Video signals require a large transmission bandwidth for transmission. So modulation of video signals is possible only by amplitude modulation. It is executed using Vestigial Sideband modulation, where either of the two sidebands is fully transmitted and the other sideband is partly transmitted.
2. What you understand by the term discone antenna?
a) combination of disc and cone
b) combination of disc and cone with a spacing of ʎ/4
c) combination of disc and cone with a spacing of ʎ/2
d) same as a simple antenna
Explanation: Discone antenna is a combination of disc and cone. A discone antenna is a version of a biconical antenna in which one of the cones is replaced by a disc. It is usually mounted vertically, with the disc at the top and the cone beneath. It is usually vertically mounted, with disc at top and the cone beneath.
3. A system has a voltage of 15V and it produces a total current of 1300μA. Find the power of system?
Explanation: Electrical power is the rate at which electrical energy is converted to another form, such as motion, heat, or an electromagnetic field.
Power, P = 15 x 1300 x 10-6 = 0.0195W.
4. An input resistance of 20 Kῼ causes a noise voltage of 10μV. Suppose two input resistance each of 20 Kῼ are connected in parallel, then find the total noise voltage?
Explanation: Thermal noise is distinct from shotnoise, which consists of additional current fluctuations that occur when a voltage is applied and a macroscopic current starts to flow.
5. Modem is combination of both modulator and demodulator.
Explanation: A modem (modulator-demodulator) is used to modulate one or more message signals using one or more carrier waves on the transmitting side. It also demodulates the received encoded signal to get the original information signal.
6. Any signal and its Hilbert transform are mutually orthogonal.
Explanation: Hilbert Transform of any signal produces a signal which has same amplitude as that of the original signal but suffers a phase-shift of -90 degree. Consider f(t) be any signal and fh(t) is it’s Hilbert transform.
If we integrate both of them under proper boundary conditions, we get 0 which shows that both are mutually perpendicular i.e.
7. What Squelch circuit does?
a) helps to receive signals that are useful for the system
b) helps to make channel noise free
c) helps to receive two or more than two signals at once
d) helps to suppress the audio output in the absence of sufficiently strong desired signal
Explanation: A Squelch is a circuit which is a mean to impede, but not destroy a signal. It circuit blocks the output in the absence of sufficiently strong desired signal. It is widely used in two-way radios to suppress the annoying sounds.
8. Mostly used radio receivers are?
a) pulsed receivers
b) CW receivers
c) TRF receivers
d) super heterodyne receivers
Explanation: Superheterodyne Receivers are radio receivers that use frequency mixing to convert a received high frequency signal to a fixed lower intermediate frequency which can be processed more conveniently. It is also the most used receivers. It is used in a variety of applications from broadcast receivers to two-way radio communication links as well as many mobile radio communications systems.
9. Find the step size of a signal with peak to peak amplitude of 4V and is quantized into 64 levels?
a) 32.3 x 10-3
b) 30.23 x 10-3
c) 62.5 x 10-3
d) 53.3 x 10-3
Explanation: Step size is the voltage difference between one digital level (i.e. 0001) and the next one (i.e. 0010 or 0000). Quantization step size is the smallest possible difference in amplitude.
10. If the step size of a system is 0.0625, find its quantization power?
a) 3.25 x 10-3
b) 3.25 x 10-4
c) 3.25 x 10-2
d) 3.25 x 10-1
Explanation: Quantization noise is a model of quantization error introduced by quantization in the analog-to-digital conversion (ADC) in telecommunication systems and signal processing. It is a rounding error between the analog input voltage to the ADC and the output digitized value.
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