# Analog Communications Questions and Answers – RF Mixing

This set of Analog Communications Multiple Choice Questions & Answers (MCQs) focuses on “RF Mixing”.

1. For a periodic function, the spectral density and auto-correlation functions are ________
a) Laplace transform pair
b) Fourier transform pair
c) Gauss transform pair
d) Z-transform pair

Explanation: Fourier transform breaks a function into an alternate representation, characterized by sine and cosines. If a function is periodic, the spectral density and auto-correlation functions are Fourier transform pair.

2. Spectral density express ________
a) Average voltage
b) Average power in a waveform as a function of frequency
c) Average noise voltage
d) Average channel capacity

Explanation: Power Spectral Density (PSD) of any signal describes the power present in signal as a function of frequency.

3. For a Gaussian process, auto correction also implies _________
a) Statistical dependance
b) Statistical independence
c) Statistical distribution
d) Ergodic process

Explanation: For a Gaussian process, auto correction implies statistical independence. It is basically a stochastic process.

4. What will be the value of modulation if we want maximum undistorted transmitted power?
a) 0
b) 1
c) 0.2
d) 0.5

Explanation: For getting maximum undistorted power in any modulated system, then the modulation index of that system should be 1. Thus, the signal should be 100% modulated.

5. For providing two or more voice circuits on the same carrier, we can use _________
a) SSB
b) ISB systems
c) DSB-SC
d) VSB

Explanation: ISB systems refers to Independent Sideband Mode and is used to provide the same carrier to two or more voice circuits.

6. The output stage of television transmitters is most likely to be a __________
a) Grid modulated class C amplifier
b) Grid modulated class A amplifier
c) Plate modulated class C amplifier
d) Plate modulated class A amplifier

Explanation: The output stage of television transmitters are basically class C amplifiers. It is grid modulated.

7. Modulation is used to separate differing transmission.
a) True
b) False

Explanation: Modulation is the property of varying one or more properties, like amplitude, frequency or phase of a periodic waveform, known as a carrier wave, with respect to the amplitude of the wave to be transmitted. It is used for separating different transmission.

8. A function f(x) is odd, when?
a) f(x) = -f(x)
b) f(x) = f(-x)
c) f(x) = -f(x)f(-x)
d) f(x) = f(x)f(-x)

Explanation: Geometrically a function f(x) is even, if plot of the function is symmetric over y-axis. Algebraically, for any function f(x) to be even, f(x) = f(-x).
While for a function f(x) to be odd, f(x) = -f(-x).

Sanfoundry Global Education & Learning Series – Analog Communications.