Communication Channels Interview Questions and Answers:

1. What is optical communication?

Ans. A system of communication in which optical carrier waves are used for transmission of information from one place to another is called as optical communication.

2. What is an optical fiber?

Ans. Optical fiber is a glass or plastic fiber that is designed for guid­ing light along its length by total internal reflection.

3. Define acceptance angle with reference to optical fiber.

Ans. The acceptance angle may be defined as the maximum angle that a light ray can have, relative to the axis of fiber so that it may propagate down to the fiber length.

4. Give relation between NA and acceptance angle

Ans. Numerical aperture, NA is the sine of the acceptance angle i.e. NA = Sin i_o

where i_o is the acceptance angle.

5. Give the classification of the optical fibers on the basis of modes.

Ans. On the basis of modes, the optical fibers are classified as mul­timode fibers and monomode fibers.

6. Give the advantages of optical fibers.

Ans. The advantages of optical fibers are: small size and weight, flexibility, electrical isolation, security and low transmission loss.

7. Give the applications of optical fibers.

Ans. Optical fibers find wide use in communication, as sensors for measurement of strain, pressure, temperature and other physi­cal parameters, as optical gyroscope, decoration purposes and as light guides in medical and other applications where bright light needs to be shined on a target without a clear line-of­-sight path.

8. What is the principle of optical fiber?

Ans. The principle of optical fiber is the total internal reflection. The physics principle of total internal reflection ensures that the fiber acts as a pipe that does not let the light pass through the walls and so be lost.

9. What are the different devices which are used as optical detector?

Ans. The devices used as the optical detectors are:

• Photoconductor
• PIN diode
• Avalanche photodiode

10. What do you mean by a satellite system?

Ans. The satellite is nothing but a spacecraft which is having the different electronics equipment’s. A satellite system represents the careful and finely tuned integration of electronics, mechanical structure, rocketry and antenna design, supported by a system of earth-based ground stations, computers and radar for tracking satellite position precisely.

11. What is meant by subsatellite point?

Ans. The subsatellite point is the place where a line drawn from the centre of the earth to the satellite passes through the earth’s surface. For an ideal geostationary satellite the subsatellite point is on the equator at some fixed longitude.

12. What is the passive satellite?

Ans. Passive satellite is nothing but a metallized balloon or metallic sphere (i.e. metal coated plastic balloons) and is used as passive reflector. It simply reflects back the signal from one region of the earth to the other region.

13. What is the active satellite?

Ans. The active satellite has antenna system, transmitter and power supply and works as an active microwave repeater, relays the signal to the receiving station either instantaneously or after storage in its memory and waiting until the satellite face the earth based receiving station.

14. What is cellphone?

Ans. The compact cellphone is a very complex piece of digital engineering which has been made possible by advanced ICs and advancement in telecom technology. As a matter of fact the handset can be thought to consist of two units—the mobile terminal (or the phone itself) and the subscriber identity module (SIM).

15. What is SIM?

Ans. The SIM is a credit card-sized plastic module which fits into your mobile phone. This SIM is ‘smart card’, and consists of all the subscriber related information, like your cellular identification number and other preferences. It can also be used for storing messages and phone numbers.

It also enables charges to be automatically billed to the cardholder, regardless of who owns the phone. This means that if your handset is out of order, you can always use any other handset with your SIM card without affecting the other person’s billing.

16. What is multiplexing in telemetering system?

Ans. Transmission of two or more messages at the same time over a single interconnecting link is called the multiplexing in telemetering system i.e. multiplexing is a method of transmitting more than one measurement over a single transmission channel.

17. What do you understand by “Time division multiplexing” and “Frequency division multiplexing”?

Ans. In TDM, samples of different measurements are transmitted serially one after the other on the same communication channel in a predetermined sequence and in this way cycle repeats itself again and again. So samples of each measurand are transmitted after a fixed period of time and the time period between two samples of a measurand should be sufficiently small so that the magnitude of measurand does not change considerably during this time.

In frequency division multiplexing (FDM), several information’s can be simultaneously transmitted using different car­rier frequencies and employing usual modulation techniques. Each of the method makes use of specific frequency band for the modulation of the frequency by the signal under measure­ment. By suitable choice of the magnitudes of the different carrier frequencies, several data may simultaneously be trans­mitted over a communication link.