The length of a half wave dipole antenna is 0.5 m. Calculate the optimum transmission frequency.

3

(a)

What should be the length of the dipole antenna for a carrier wave of frequency \(3\times10^{ 8 }\)Hz?

3

(a)

A sinusoidal voltage amplitude modulates another sinusoidal voltage of amplitude 2 kV resulting in two side bands of amplitude 200 V. Find the modulation index.

3

(a)

A band width of 5 MHz is available for AM transmission.If the maximum audio signal frequency used for modulating the carrier is not to exceed 5 kHz,how many stations can be broadcast within this band simultaneously without interfering with each other?

3

(a)

In a diode detector,output circuit consisits of \(R=1M\Omega \) and C=1 pF.Calculate the carrier frequency it can detect.

3

(a)

The carrier frequency of a station is 50 MHz.A resistor of \(10k\Omega \)and a capacitor drops to 10 pF are available in the detector circuit.Is it good enough for detection?

3

(a)

A ground receiver station is receiving a signal at (a) 5 MHz and (b) 100 MHz, transmitted from a ground transmitter at a height of 400 m located at a distance of 125 km. Identify whether it is coming via space wave or skywave propagation or satellite transponder. Radius of earth =\(6.4\times{ 10 }^{ 6 }m\); maximum number density of electrons in ionosphere = \({ 10 }^{ 12 }{ m }^{ -3 }\)

3

(a)

Frequencies in the UHF range normally propagate by means of
(a) ground waves (b) sky waves  (c) surface waves  (d) space waves

3

(a)

For an optical communication system, operating at \(\lambda =800\ nm\), only 1% of the optical source frequency is the available channel bandwidth. How many channels can be accomdated for transmitting video T.V. signal requiring an approximate bandwidth of 4.5 MHz?

3

(a)

What is a ground wave? Why short wave communication over long distance is not possible via ground waves?

3

(a)

Define the critical frequency in relation to sky wave propagation of electromagnetic waves.On a particular day, the maximum frequency reflected from the ionosphere is 10 MHz.On another day, it was found to decrease to 8 MHz.Calculate the ratio of the maximum electron densities of the ionosphere on the two days.

3

(a)

What is space wave propagation? Give two examples of communication system which uses the space wave mode.A TV tower is 80 m tall.Calculate the maximum distance upto which the signals transmitted from the tower can be received.

3

(a)

An audio signal of amplitude 0.1 V is used in amplitude modulation of a carrier wave of amplitude 0.2V.Calculate the modulation index.

3

(a)

A modulating signal is a square wave as shown in the figure.
The carrier wave is given by c(T) = 2 sin (8\(\pi \) t) volt.

(i) Sketch the amplitude modulated waveform
(ii) What is the modulation index?

3

(a)

An amplitude modulated wave is as shown in the figure.Calculate
(i) the percentage modulation
(ii) peak carrier voltage and 
(iii) peak value of information voltage.

3

(a)