Digital Communication Viva Questions

 

Digital Communication Lab Viva Questions with Answers

 

1.  List down the major advantages and disadvantages of analog communication techniques?

The major advantages of analog communication are:

(a) For audio and video transmission, analog signals are mostly suited

(b) It can be ported easily

(c) They can be processed easily

(d) Bandwidth usage is less than digital signals

(e) For analog signals, the need of new graphics board is not necessary.

(f) Analog signals can present more refined information because of its higher density

Electrical Measurements Lab Viva Questions and Answers

 

Electrical Measurements and Instrumentation Lab Viva Questions and Answers

 

1. What you know about the Cathode ray oscilloscope (CRO)?

Basically the Cathode ray oscilloscope (CRO) is considered as the 'eye' of an electronics engineer. An electronics engineer can see all the signals and waveforms with the help of CRO. Initially it was known as Oscillograph.  The use of CRO is for the measurement and analysis of waveforms, for display and other phenomenon in electrical and electronic circuit. CRO has 4 sections namely display, vertical controllers, horizontal controllers and triggers. Probes are used for input and output measurements in CRO. the waveform is plotted in CRO by plotting amplitude 'A' on x axis and time 't' on y-axis. The main applications of CRO are: Radio, TV Receivers, etc.

 

Applications of Lasers in Scientific Field

Applications of Lasers in Communication, Space, Surgery, Military...

The ingenious principle of laser was first worked out in 1958 by Charles Townes of Columbia University. He made use of this principle a few years earlier in 1953 to invent a very similar device- maser where microwaves are used instead of light waves. Hence laser is an optical maser. The first successful laser using a large synthetic ruby crystal was built by Teodore H Maimann in 1960. With the discovery of laser man's control of light has been and will continue to extend to an unpredictably large and diverse number of applications in scientific field.

(i) Communication :

Since light from the laser is coherent it can theoretically carry messages in the same manner as comparatively low frequency carriers. The frequency of the laser is so high that each message or band of frequencies is a very small percentage of the carrier frequency. Hence a large number of messages can be sent. It can accommodate millions of television channels.

(ii) Space exploration :

Rockets and satellites can be efficiently controlled by laser beam.

(iii) Measurement of large distances

Distance between earth and other planets can be accurately measured by laser beam because it is highly collimated.

(iv) Welding

The laser can be used effectively for spot welding. It possible to weld a joint even after the joint has been sealed inside glass envelope.

(v) Hole drilling

A sharply focused laser beam can be used to cut holes in diamond and other hard materials,

(vi) Surgery

(a) Tooth drilling : The beam destroys by vaporization the dark decayed spot.

(b) Eye - Surgery : Eye - tumors can be removed and detached retina of human eye can be welded by low power laser beam. The Lasik surgery is nowadays used in treating the defects of eye by correcting the shape of the cornea of the eye using laser beam to get sharp image of an object exactly on the retina of the eye.

(c) Cancer treatment : Laser beam can remove some cancerous cell instantly, accurately, and without pain or bleeding.

(vii) Thermonuclear fusion

Laser can he used to trigger a thermonuclear fusion.

(viii) Military applications

The laser beam can be used to destroy an attacking missile in space. Moreover it can be used as 'death-ray gun' to destroy enemies.

(ix) Photography

Laser beam can be used to produce three dimensional images without the use of lenses. This process is called Holography.

(x) Science

(i) Chemical reactions can be accelerated by exposing it to the laser beam.

(ii) Laser can he used to study Raman effect.

Doppler Effect in Light | Redshift and Blueshift

Doppler Effect in Light

We are already familiar with the Doppler effect in sound i.e., the apparent change in frequency of sound due to the relative motion between the source and the listener in a medium. It is named so, because of Doppler who was the first to have stated a theory in the case of sound waves in the year, 1842. He pointed out the relevance of the phenomenon in the case of light.

If the source of light (source of em waves) of frequency f is stationary and the observer moves towards the source with a velocity v (v << c, the velocity of light), the apparent frequency of light as observed by the observer,

f‘ = f(1 + v/c)

The above equation is also valid in the case when the source moves towards the stationary observer. If the source moves away from the stationary observer or the observer moves away from a stationary source,

f‘ = f(1 - v/c)

Doppler effect in sound is asymmetric whereas the Doppler effect in light is symmetric. It means that the apparent frequency of sound when the source is approaching a listener at rest and the apparent frequency when the listener is approaching the source at rest are different. But, for light, the source approaching the observer and observer approaching the source exhibit exactly the same Doppler change in the frequency.

Doppler effect is a convenient tool to estimate the speed and direction of motion of stars, planets etc. in our universe relative to us. In general, if the wavelengths of light received from these objects shift towards the red end of the spectrum, these objects are moving away from the earth. This is known as Redshift. If the wavelengths of spectral lines emitted by these objects shift towards the violet end of the spectrum, these objects are moving towards the earth. In the case of stars, the red shift is observed. This shows that stars are moving away from the earth. By finding the shift, the velocity of these heavenly bodies can be estimated. When waves are received from a source which is moving in the direction of the observer, then there would be an apparent decrease in the wavelength. This is referred to as Blueshift.

The Doppler effect finds application to estimate the speed of aeroplane and automobiles, track artificial satellites, estimate the velocity and rotation of the sun etc.