Qn 1.

Which of the following is used for the line-of–sight (LOS) communication?

a. Sky waves b. Ground waves c. Space waves d. Long waves

b) ...............Signals are continuous variations of voltage or current

Qn 2.

What is the population covered by the transmission , if the average population density around the tower is 1200 km2? The antenna height is 160 m.

Qn 3.

Television broadcast is done by space wave mode of propagation.

a) What is the difference between sky wave and space wave modes of propagation?

b) A TV transmission antenna is 81 m tall. How much service area can it cover if the receiving antenna is at the ground level? (Radius of earth is 6400km)

Qn 4.

Spectrum allocations for communication are arrived at by an international agreement.

a) Name the agency which administers the present system of frequency allocations.

b) Draw block diagrams of an amplitude modulated

i) Transmitter and

ii) Receiver

Qn 5.

In our daily life, modulation plays an important role.

a) What do you understand by amplitude modulation?

b) Give a block diagram of a generalized communication system.

Qn 6.

a) A receiver in a communication system must have

(i) Pick-up antenna (ii) demodulator (iii) amplifier (iv) all of these

(b) Which of the following statement is wrong?

(i) The attenuation of surface waves increases with increase in frequency.

(ii) The phenomenon involved in sky wave propagation is similar to total internal reflection.

(iii) Space wave mode of propagation is used in satellite communication.

(iv) Sky wave propagation is useful only in the range of frequencies 30 to 40 MHz

 

Qn 7.

Draw the labelled block diagram of an amplitude modulator for obtaining AM wave.

Qn 8.

A male voice after modulation sounds like that of a female to the receiver. The problem may be due to

a) poor selection of modulation index. b) poor bandwidth selection of amplifiers. c) poor selection of carrier frequency d) loss of energy in transmission.

Qn 9.

Draw truth table for the given circuit