COMMUNICATION ENGINEERING-II
Very Short Answer Type Question (2 Marks Each, about 30- 40 words)
1. Define Microwave.
Ans 1: Microwaves are the electromagnetic waves with wavelength ranging from one meter to one millimeter & with frequency ranging from 1GHz to 1000 GHz.
2. What are the applications of Microwaves?
Ans 2: Microwaves are used for:
(i) Communication: Microwaves are used in long distance as well as short distance Communication such as telecommunication, broadcasting for television etc.
(ii) It is used in remote sensing for weather forecasting and RADAR.
(iii) It is used in heating application such as cooking using oven, baking and in textile industry for drying the clothes & dyes.
(iv) It is also used in various medical applications like curing of cancer.
3. Write the frequency range of VHF, UHF, HF and SHF.
Ans 3 : The frequency ranges are:
VHF( very high frequency): 30-300MHz
UHF(ultra high frequency): 300 – 3000MHz
HF(high frequency): 3-30MHz
SHF(super high frequency): 3-30GHz
4. What are the high frequency effects in conventional tubes?
Ans 4: The high frequency effects in conventional tubes are
a) Inter Electrode Capacitance (IEC)
b) Lead Inductance(LI)
c) Transit Time
5. What is the effect of transit time?
Ans 5: There are two Effects.
i) At low frequency, the grid & anode signals are no longer 180 degree out of phase, so there is a problem to design it with feedback in oscillators.
ii) The grid starts to take power from the driving source and the power is absorbed even when the grid is also negatively biased.
6. What are the microwave sources?
Ans 6: Gunn Diode, Reflex Klystron & Magnetron are used to generate the microwave.
7. Define electron emission.
Ans 7: The liberation of electrons from the surface of substance is called electron emission.
8. Define reflex klystron.
Ans 8: Reflex klystron is a single cavity, variable frequency microwave generator. Its principle is based on velocity modulation.
9. Define TWT.
Ans 9: TWT stands for Travelling Wave Tube. The basic principle of traveling wave tube is the conversion of d.c.
10. Define Waveguide.
Ans 10: Waveguide is a hollow conducting metallic tube used for carrying electromagnetic waves. Waves propagate in the waveguide by successive reflection from the inner walls of the tube.
11. What are group velocity and phase velocity?
Ans 11: Phase Velocity: It is defined as the rate at which the wave propagates through the wave guide. It is given by Vp = w/ρ
Group velocity: It is defined as the rate at which the waves propagate through the waveguide. It is given by Vg = dw/dβ
12. Define TEM mode.
Ans 12: TEM(Transverse Electromagnetic) :- In TEM mode, both the electric and magnetic components are purely transverse to the direction of propagation. There are no field components in z- direction i.e. Ez=0 and Hz=0 . Also Ex=Hx=Ey=Hy=0.
13. Define Guide Wavelength.
Ans 13: Guide wavelength is defined as the distance traveled by the wave in order to undergo a phase shift of 360˚.
14. List two microwave devices using Faraday rotation principles.
Ans14: Isolator and Circulator.
15. What is Hybrid TEE?
Ans15: Hybrid TEE or Magic TEE is formed by combining E-plane tee and H- plane tee. It act as a four port hybrid circuit.
Diagram:
16. Define isolator.
Ans 16: Isolator is a 2- port device which provides very little attenuation to the signal travelling from port 1 to port 2 and provides very high attenuation to the signal travelling from port 2 to port 1.
It is used to couple the microwave source to load.
17. Define waveguide attenuator.
Ans 17: A device used to control the amount of microwave powers transferred from one point to another point on a microwave transmission system is called waveguide attenuator.
It controls the microwave power either by reflecting or absorbing it.
18. Give the application of direction coupler.
Ans 18: The directional coupler are used for: i) unidirectional power measurement
ii) SWR measurement
iii) Reflectometer
iv) Balanced Duplexer
19. What is meant by Polarization?
Ans 19: It may be defined as the physical orientation of the radiated electromagnetic waves in space.
20. Define antenna.
Ans 20: Antenna is used to radiate and receive electromagnetic waves. Its main function is to connect the transmitter with receiver in space.
21. Define directive gain.
Ans 21: Directive Gain is defined as the ratio of power density of radiated electromagnetic energy of an unidirectional antenna to the power density in the same direction & same distance due to an omni-directional antenna, with both antenna radiating the same total power.
22. Define Tropospheric waves.
Ans 22: Waves that arrive at the receiver after reflection fro the troposphere region is called Tropospheric wave. These waves propagates above 10 Km from earth’s surface.
23. What is meant by fading?
Ans 23: When the strength of the signals varied on line of sight paths due to atmospheric conditions, then it is called fading.
24. What is ionospheric propagation?
Ans 24: Waves that arrive at the receiver after the propagation through ionosphere is called ionospheric Propagation. The region of ionosphere is 50 Km to 400 Km.
Ionosphere: The ionosphere is that region of earth’s atmosphere in which the constituent of gases are ionized by radiation from the outer surface.
25. What is the concept of reflection & refraction waves by the ionosphere?
Ans 25: The reflection & refraction of radio waves by the ionosphere is a function of frequency.
26. Define MUF(maximum usable frequency).
Ans 26: Maximum usable frequency (MUF) is the highest frequency that can be used for sky wave propagation between two specific points on earth’s surface.
27. Define ground/surface waves.
Ans 27: A ground wave is an electromagnetic wave that travels along the surface of earth. The ground waves are also known as surface waves.
28. What is radar?
Ans 28: RADAR stands for Radio Detection And Ranging. Radar is an electromagnetic system that is used to determine the location of the target such as aircraft, ships, vehicles, spacecrafts etc. It operates by radiating energy into space and detecting the echo signal reflected from the target.
29. What do you mean by maximum unambiguous range?
Ans 29: The echoes that receives after the transmission of the next pulse are called second time around echoes. The range beyond which the targets appear as second time around echoes is called maximum unambiguous range, which is given by
Runambg = cT = _c_
2 2f
30. What are the applications of radar?
Ans 30: i) Military application
ii) Remote Sensing
v) Air Traffic control (ATC)
vi) Aircraft & ship safety
vii) Police radar
viii) space
31. What are stalo & coho?
Ans 31: Stalo: Stalo is the Stable Local Oscillator which is used to recognize the need for high stability in MTI receiver.
Coho: Coho stands for Coherent Local Oscillator which is used as reference signal in MTI receiver that has the phase of transmitted signal.
32. Define blind speeds.
Ans 32: The limitation of single pulse radar system results in target speeds called blind speed, where the target will not be detected and there will be an cancelled clutter residue that can interfere with the detection of targets.
33. What is clutter?
Ans 33: When radar detects the target, it receives the echo signals from the natural environment such as land, sea & weather, which is more than receiver noise. Then, these echoes are called clutter.
34. What is MTI radar?
Ans 34: MTI stands for Moving Target Indicator. MTI radar is used for detecting moving targets such as aircrafts. This radar uses Doppler effects for its operation.
35. What is PPI?
Ans 35: PPI stands for Plan Position Indicator. The PPI is a presentation that maps in polor coordinates the location of the target in azimuth angle & range.
36. What is VSAT?
Ans 36: VSAT stands for Very Small Aperture Terminal. The earth station with antenna aperture diameters of less than 100 wavelengths was called VSAT.
VSAT is a communication network that allows multimedia traffic data to brought directly to the user.
37. Define apogee & perigee.
Ans 37: The point farthest from earth is known as apogee.
The point closest from earth is known as perigee.
38. What is an orbit?
Ans 38: Orbit is the path of the body acted upon the force of gravity. Generally, it is the continuous path of an object.
39. What is meant by transponder?
Ans 39: In a communication satellite, the device which provides the communication link between the satellite’s transmitting & receiving antenna is known as transponder.
40. Define diplexer.
Ans 40: The transmit & receive signals are separated in a device is called diplexer.
41. What are the methods of multiple access techniques?
Ans 41: FDMA (Frequency division multiple access technique)
TDMA (Time division multiple access technique)
CDMA (Code division multiple access technique)
42. Define guard time.
Ans 42: Guard Time is a very small time in between two bursts that is used to prevent the bursts from overlapping.
43. What are the Kepler’s Laws of planetary motion?
Ans 43: Kepler’s Ist Law: It states that the orbit of satellites is in ellipse with the centre of the earth at one focus.
Kepler’s IInd Law: It states that The line joining the centre of earth & the satellite sweeps over equal areas in equal time intervals.
Kepler’s IIIrd Law: It states that the square of the orbital periods of two satellites have the same ratio as the cubes of their mean distances from the centre of earth.
44. What are the applications of VSAT?
Ans 44: i) VSAT’s system are used to connect the business & their different departments such as store with a central computer system so that they can share some information.
ii) VSAT’s are used to handle small traffic data.
