Communication Systems - Modern Physics - Physics Previous Year Questions

A message signal of frequency 15 kHz is used to modulate a carrier of frequency $v_c$. If the side bands produced are 1515 kHz and 1485 kHz , then $v_c$ is

A TV transmission antenna is 40 m tall. How much service area is can cover, if the receiving antenna is at the ground level?

(radius of the earth $=6400 \mathrm{~km}$ )

The need for modulation is

A telephonic communication service is working at a carrier frequency of 20 GHz . Only $20 \%$ of it is utilised for transmission. If each channel requires a bandwidth of 5 kHz , then the number of telephonic channels that can be transmitted simultaneously are

The loss of strength of a signal while propagating through a medium is known as

Consider the following statements regarding digital signals

(i) provide a continuous set of values

(ii) represent values as discrete steps

(iii) can utilise binary system

(iv) are in the form of rectangular waves

Then the true statements are

An amplitude modulated wave is represented by $c_m(t)=10[1+0.6 \sin (1250 t)] \sin \left(10^8 t\right)$. Then modulation index is

Assertion (A) Television signals are received through sky-wave propagation.

Reason (R) The ionosphere reflects electromagnetic waves of frequencies in the range ( $3-30) \mathrm{MHz}$.

Choose the correct option.

A message signal of frequency 10 kHz and peak voltage of 15 V is used to modulate a carrier frequency of 1 MHz and peak voltage of 30 V . Determine the modulation index.

Which of the following statements is not true?

The range of frequency bands used for standard AM broadcast is

For an amplitude modulated wave, the modulation index is found to be 0.5 . If the maximum amplitude is found to be 10.0 V , then the minimum amplitude is

A carrier wave of peak voltage 10 V is used to transmit a message signal. What should be the peak voltage of the modulating signal in order to have a modulation index of $80 \%$ ?

The electromagnetic waves of frequency 6 GHz are used in

A message signal is super-imposed with a carrier signal. The resulting modulating signal $C_m(t)$ is given by $C_m(t)=A_1 \sin \left(\omega_1 t\right)+A_2 \sin \left(\omega_2 t\right)-A_2 \sin \left(\omega_3 t\right)$, where $\omega_2<\omega_1<\omega_3$. The modulation index and the angular frequency fo the message signal respectively, are

The function of a detector is to demodulate the modulated carrier wave and the steps for this process are

A message signal of frequency $50 / \pi \mathrm{kHz}$ and peak voltage of 5 V is used to modulate a carrier of frequency 1 MHz and peak voltage 20 V . The modulation index is