Umakant Kondapure, Collin Fernandes, Nipun Bhatia, Vikram Bathula and, Ketki Deshpande Solutions for Chapter: Communication Systems, Exercise 4: Evaluation Test

Amplitude modulation is useful for broadcasting in communication systems because,

Assertion: Communication in UHF/VHF regions can be established by space wave or tropospheric wave.

Reason: Communication in UHF/VHF regions is not limited to line of sight distance but can be achieved for very large distances.

In satellite communication,
(i) the frequency used lies between $6 \mathrm{MHz}$ and $10 \mathrm{MHz}$,
(ii) the uplink and downlink frequencies are different,
(iii) the orbit of geostationary satellite lies in the equatorial plane at an inclination of $0°$.
In the above statements,

Assertion: A dish antenna is highly directional.

Reason: A dipole antenna is unidirectional.

Assertion: Modulation index is the degree to which the carrier wave is modulated.

Reason: For strong and clear reception, the value of modulation index should be very small.

In an amplitude modulated wave for audio frequency of $400 \mathrm{cycles} {\mathrm{second}}^{-1}$, the proper carrier frequency will be,

A sinusoidal carrier wave of frequency $1 \mathrm{MHz}$ and amplitude $100 \mathrm{V}$ is amplitude modulated by sinusoidal voltage of frequency $4 \mathrm{kHz}$ producing $50 \%$ modulation. The frequencies of lower and upper side-bands are, respectively,

The total population covered by the T.V. tower of height $200 \mathrm{m}$ if the population density around it is ${10}^3 {\mathrm{km}}^{-2}$ is (radius of the earth is $6.4\times {10}^6 \mathrm{m}$),