Which of the following frequencies will be suitable for beyond the horizon communication using sky waves.

Frequencies in the UHF range normally propagate by means of:

A message signal of frequency \({ \omega }_{ m }\) is superposed on a carrier wave of frequency \({ \omega }_{ c }\) to get an amplitude modulated wave (AM). The frequency of the AM wave will be

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

An audio signal of 15kHz frequency cannot be transmitted over long distances without modulation because

What is varied in an FM wave?

What is modulation index of an FM wave?

Name three different compression techniques used in fax.

Which of the two-----AM or FM is preferred for high fidelity reception?

Name the device which can represent digital data by analog signals and vice versa.

AM and FM transmission are said to be 'real time systems'.Why? 

A carrier wave of peak voltage 12 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 75%?

" A communication satellite is essentially a repeater station in space." Justify the statement by analysing the function of a repeater.

Define modulation index. Why is it kept low? What is the role of a bandpass filter?

A message signal of frequency 10 kHz and peak voltage 10 V is used to modulate a carrier wave of frequency 1 MHz and peak voltage 20 V. Determine
(i) The modulation index
(ii) the side bands produced.

A 1000 kHZ carrier is modulated with 800 Hz audio signals.What are the frequencies of first pair of side bands?

Explain the following terms in relation to the use of internet?

A radio set can be turned to any station in the frequency range 6 MHz to 12 MHz band.What is the corresponding wavelength band of radio set?

Distinguish between sky wave and space wave propagation. Explain in brief with
the help of suitable diagram, how space waves are used for line of sight communication?

Explain with reason
(i) In amplitude modulation, the modulation index μ is kept less than or equal to 1.
(ii)  The maximum amplitude of an amplitude modulated wave is found to be 15V while its minimum amplitude is found to be 3 V. What is the modulation index?
(iii) Why amplitude modulated signal be noisier than a frequency modulated signal upon transmission through a channel?

In the famous conversation, Rakesh Sharma, the first Indian Astronaut in space, was asked by the Prime Minister Indira Gandhi as to how India looked from space.To which he replied,'Sare Jahan Se Achcha' (better than the whole world).
Read the above passage and answer the following questions:
(i)   Which scientific mode of communication enabled the Prime Minister to speak to the Astronaut?
(ii)   Name the scientific values displayed in this anecdote.
(iii) Which values are being reflected in the reply given by the astronaut?
(iv) Give one more example of this scientific mode of communication in everyday life situations.

Raj was cycling from his village to a neighbouring village.On the way, he met an old man who was walking in the direction of the same neighbouring village. Raj invited the old man to sit on his cycle and took him to the neighbouring village.The old man got down from the cycle, thanked Raj and gave him blessing.
Read the above passage and answer the following questions:
(i)  What are the values displayed by Raj?
(ii) Can you relate the given paragraph with the process of modulation?

One day Samir though if Moon is a natural satellite then why there is need of other artificial satellites. finally, he came to the conclusion that Moon cannot be used as a communication satellite. So, he requested his teacher for its answer.The teacher explained him the the reasons behind it properly, after which he shared his knowledge with his classmates.
(a) What are the value shown by Samir?
(b) Why can Moon be not as a communication satellite?