# Analog Communications Questions and Answers – Time Domain Description

This set of Analog Communications Multiple Choice Questions & Answers (MCQs) focuses on “Time Domain Description”.

1. Distance between direct broadcasting satellite and earth’s surface is ________
a) 4500km
b) 33000km
c) 5200km
d) 36000km

Explanation: Satellite broadcasting takes place between directional parabolic antennae, where the signal is sent via cable to antennae which beams it to the satellite and then the satellite sends back a signal to another location on Earth. A communication satellite amplifies radio telecommunications signals with the help of a transponder. The distance between it and earth’s surface is approximately 36000km.

2. UHF stands for ________
a) Ultra High Electric Field
b) Ultraviolet High Frequency
c) Ultra High Frequency
d) Ultra High Magnetic Field

Explanation: Ultra High Frequency (UHF) are frequencies at ultra high levels, thus consisting of radio frequencies in the range of 300 MHz and 3 GHz. Rest of the options don’t have any existence.

3. What is the ITU designation range for VHF?
a) 30 to 300 Kilohertz
b) 300 to 3000 Kilohertz
c) 30 to 300 Megahertz
d) 3 to 30 Megahertz

Explanation: The VHF (Very High Frequency) are frequencies in the range of 30 MHz to 300 MHz. Frequencies in the range 30 to 300 Kilohertz belong to LF (Low Frequency) range, whereas frequencies in the range 300 to 3000 Kilohertz belong to MF (Medium Frequency) range. Frequencies in the range 3 to 30 Megahertz belong to HF (High Frequency) range.

4. Effective noise at high frequencies is ________
a) Johnson noise
b) Flicker noise
c) transit-time noise
d) Partition noise

Explanation: Transit-time noise is alike to shot noise, and results if the time taken by electrons to reach from emitter to collector is comparable to the period of signals being amplified. Thus, transit-time noise occurs at high frequencies, whereas Flicker noise occurs below a few kilohertz and Johnson noise, also known as thermal noise, occurs at all frequencies.

5. VHF stands for ________
a) very high frequency
b) very high electric field
c) very high magnetic field
d) very high electromagnetic field

Explanation: The VHF (Very High Frequency) are frequencies in the range of 30 MHz to 300 MHz. Rest options don’t have any existence.
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6. Which among the following is the Analog Continuous Modulation technique?
a) PAM
b) PCM
c) AM
d) PM

Explanation: Only AM (Amplitude Modulation) is Analog Continuous Modulation technique while rest are Digital Modulation techniques. In AM, the amplitude of a carrier wave is varied with respect to the instantaneous amplitude of the message signal. This is how amplitude modulation takes place.

7. ITU stands for ________
a) Indian Telecommunication Union
b) Indian Telephonic Union
c) International Telephonic Union
d) International Telecommunication Union

Explanation: The International Telecommunication Union (ITU) is an United Nations agency serving to correlate all operations regarding telecommunication and provide services all over the world. Rest options are all invalid.

8. If AM transmitter has low level modulation then it has ________
a) high efficiency
b) poor efficiency
c) high modulating power
d) high resistance towards noise

Explanation: In low-level modulation, the generated amplitude modulated signal utilizes less power, followed by the AM signal being amplified by a chain of linear amplifiers. However, in high power applications, the amplifiers that follow the modulator stage will be linear amplifiers which will render the whole modulation as inefficient.

9. Radiation resistance of an antenna is ________
a) a dc resistance
b) an ac resistance
c) a constant value
d) neither ac nor dc resistance

Explanation: Radiation resistance is that part of an antenna that is caused by the radiation of electromagnetic waves from the antenna. It is considered to be an equivalent resistance dissipating the same amount of power as an actual antenna would have radiated. Radiation resistance of an antenna is usually an ac resistance.

10. What do you understand by isotropic antenna?
a) it radiates its power uniformly in all directions
b) it radiates its power non-uniformly in all directions
c) it radiates its power specifically in one direction only
d) it does not radiate any power

Explanation: An isotropic antenna is considered to be an ideal antenna that radiates power uniformly in all directions. Generally, this type of antenna does not exist. However, it is often used to determine certain antenna characteristics like antenna gain.

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