# ELECTRONICS AND COMMUNICATION ENGINEERING IMPORTANT MCQ-MICROWAVE COMMUNICATION

1. __________ is the progressive decrease of signal strength with increasing
distance.

B. Attenuation
C. Modulation
D. Propagation

2. Calculate the effective earth’s radius if the surface refractivity is
301.

A. 8493 km
B. 8493 mmi
C. 6370 km
D. 6370 mi

3. If k-factor is greater than 1, the array beam is bent

A. Away from the earth
B. towards the ionosphere,
C. towards the earth
D. towards the outer space

4. the antenna separations (in meters) required for optimum operation of a
space diversity system can be calculated from:

A. S = 2λR/L
B. S = 3λR/L
C. S = λR/RL
D. S = λR/L
where R = effective earth radius (m) and L = path length (m)

5. Rainfall is an important factor for fading of radio waves at frequencies
above

A. 10 GHz
B. 100 GHz
C. 1 GHz
D. 100 MHz

6. Theoretically electromagnetic radiation field strength varies in inverse
proportion to the square of the distance, but when atmospheric attenuation
effects and the absorption of the terrain are taken into account the
attenuation can be as high as the inverse _______ power of the distance.

A. Third
B. Fourth
C. Fifth
D. Sixth

7. What do you call an attenuation that occurs over many different
wavelengths of the carrier?

8. Which of the reception problems below that is not due to multipath?

C. Random Doppler shift

9. Which causes multipath or frequency-selective fading?

A. Small reflector
B. Nearer reflector
C. Further reflector
D. Large reflector

10. In microwave transmission using digital radio, what causes most
intersymbol interference?

C. Random Doppler shift

11. A shipboard equipment which measures the distance between the ship’s
bottom and the ocean floor.

A. Fathometer
B. Echosounder
C. LORAN
D. SONAR

12. The cavity resonator

A. Is equivalent to an LC resonant circuit
B. In a reflect klystron has its output taken from the reflector plate
C. Produces a frequency which is independent of the cavity size.
D. Has a low Q factor for narrow operation.

13. At what position is the input signal inserted into a traveling-wave
tube?

A. At the cathode end of the helix
B. At the collector
C. At the collector end of the helix
D. At the control grid of the electron gun

14. Coupling into and out of a traveling-wave tube can be accompanied by a

A. Waveguide match
B. Cavity match
C. Direct coax-helix match
D. All of the above

15. a high-power microwave pulse of the order of megawatts can be generated
by a

A. traveling-wave tube
B. magnetron
C. reflex klystron
D. Gunn diode

16. A traveling-wave tube (TWT) amplifies by virtue of

A. The absorption of energy by the signal from an electron stream
B. The effect of an external magnetic field
C. The energy contained the cavity resonators
D. The energy liberated form the collector

17. What is the purpose of the electromagnetic field which surrounds a
traveling-wave tube?

A. To accelerate the electron
B. To velocity modulate the electron beam
C. To keep the electrons from spreading out
D. To slow down the signal on the helix

18. Which of the following is used as an oscillator device in the SHF band?

A. Thyratron tube
B. Tunnel diode
C. Klystron tube
D. Both B and C

19. Microwave frequencies are normally regarded as those in the range of

A. 1 to 500 MHz
B. 1000 to 10,000 GHz
C. 1 to 100 GHz
D. 10 to 1000 GHz

20. The highest frequency which a conventional vacuum-tube oscillator can
generate is not limited by the

A. Electron transit time
C. Inter-electrode capacitance
D. Degree of emission from the cathode

21. As the electron beam moves through a klystron’s intercavity drift space

A. Frequency modulation at the input cavity creates velocity modulation at
the output cavity
B. Velocity modulation at the input cavity creates density modulation at the
output cavity
C. Density modulation at the input cavity creates velocity modulation at the
output cavity
D. Phase modulation at the input cavity creates velocity modulation at the
output cavity.

22. The frequency of the oscillation generated by a magnetron, is mainly
determined by

A. The flux density of the external magnet
B. The ratio of the dc cathode voltage to the magnetic flux density
C. The number of the cavity resonators
D. The dimension of each cavity resonator

23. If the instantaneous RF potentials on the two sides of a magnetron
cavity are of opposite polarity, the operation is in the

A. π mode
B. π/2 mode
C. 2π mode
D. π/4 mode

24. The Gunn diode oscillator

A. Is capable of generating continuous microwave power of the order of
kilowatt
B. Generates frequencies which are below 100 MHz
C. Operates over a positive resistance characteristic
D. Depends on the formation of charge domain

25. What ferrite device can be used instead of duplexer of isolate microwave
transmitter and receiver when both are connected to the same antenna?

A. Isolator
B. Magnetron
C. Simplex
D. Circulator

26. To achieve good bearing resolution when using a pulsed-radar set, an
important requirement is

A. A narrow, antenna-beam width in the vertical plane
B. A narrow, antenna-beam width in the horizontal plane
C. A low repetition rate
D. A high duty cycle

27. When used in conjunction with a radar set, the purpose of an echo box is
to provide an artificial target.

A. Which may be used to tune the radar synchronizer
C. To the tone of the pulse repetition
D. Tune the magnetron to the correct frequency

A. And FET
B. A tunnel diode
C. A silicon crystal
D. A Rochelle salts crystal

29. Klystron oscillators are most often used in the frequency range of

A. 300 to 3000 MHz
B. 3000 to 30000 MHz
C. 30 to 30000 MHz
D. 10 to 10000 MHz

30. Oscillators of a klystron tube are maintained

A. By bunches of electrons passing the cavity grids
B. By plate-to-cathode feedback
C. By feedback between the accelerating grid and the repeller
D. By circulating bunches of electrons within the cavities.

31. What allow microwave to pass in only one direction?

A. RF emitter
B. Capacitor
C. Varactor-triac
D. Ferrite emitter

32. In an SHF pulsed radar set, a reflex klystron can be used as a

A. Single mixer stage
B. Local oscillator
C. Transmitter oscillator
D. Duplexer stage

33. A Class-S Emergency Position-Indicating Radio Beacon (E.P.I.R.B)

A. Must be capable of floating or being secured to a survival
B. Must have its battery replaced after emergency use
C. May be tested during the first five minutes of any hour
D. All of these

34. A PPI cathode-ray tube as used on a radar set

A. Is used to check the percentage of modulation
B. Indicates both the range and azimuth of a target
C. Indicates only the range of a target
D. Is used for receiver alignment

35. The resonant frequency of a cavity resonator depends upon

A. The mode of operation
B. Its electrical dimensions
C. Its physical dimensions
D. The capacitor which tunes it

36. The maximum usable range of the usual radar set (on any particular range
setting) is determined by

A. The width of the transmitted pulses
B. The interval between transmitted pulses
C. The bandwidth of the receiver IF stages
D. The duty cycle

37. A reflex klystron is oscillating at the frequency of its resonant
cavity. If the reflector voltage is made slightly less negative, the

A. Oscillation will cease
B. Output power would increase
C. The frequency will decrease
D. Bunching would occur earlier in time

38. The coarse frequency adjustment of a reflex klystron is accomplished by

A. The AFC system
B. Adjusting the flexible wall of the resonant cavity
C. An adjustment in the synchronizer
D. Varying the repeller voltage

39. In a pulsed radar set, the STC circuit is used to

A. Improve the target bearing resolution
B. Increases receiver sensitivity for echoes from targets
C. Vary the pulse frequency in order to control the maximum target
D. Reduce interference from the effects of sea return

40. In a pulsed radar set, the function of the duplexer is to

A. Aid in calibrating the display unit
B. Prevent frequency drift in the klystron
C. Allow the transmitter and the receiver to operate from a common antenna
D. All of these

41. A magnetron is operated at a duty cycle of 0.001. It has a peak power
output of 100 kilowatts. Its average power is

A. 10,000 watts
B. 100 watts
C. 1,000 watts
D. 1,000,000 watts

42. The aquadag coating on the inside of PPI tube is used

A. To focus the beam of primary electrons
B. To shield the electron beam from unidirectional magnetic
C. As a second anode and to prevent the build-up of secondary field
D. All of these

43. If the duration of the radar transmitted pulse, on a particular range of
operation, is increased, the required bandwidth of the receiver’s IF amplifiers

A. Must remain as before
B. Must be increased
C. May be decreased
D. Must be doubled

44. The main frequency determining element of a klystron is

A. The repeller voltage
B. The accelerating voltage
C. Its resonant cavity
D. Its mode of operation

45. A thin layer of dirt and grime coverts the reflecting surface of the
parabolic dish of a radar set. The particular effect on the performance of the

A. A decrease in range
B. A reduction in horizontal resolution
C. No noticeable effect
D. A decrease in gain

46. Which of the following permits a microwave signal to travel in one
direction with virtually no loss, but severely attenuates any signal attempting
to travel in the reverse direction?

A. Isolator
B. Wave trap
C. Tunnel diode
D. Circulator

47. It is possible to increase the maximum range of a radar equipment by

A. Lowering the pulse frequency
B. Raising the peak power of the transmitter
C. Narrowing the beam width and increasing the pulse duration
D. All of these

48. When it is desired that short-range targets be clearly seen on a
pulsed-radar set, it is important that the receiver and display system have

A. A long time constant
B. Low-pass filters
C. The shortest possible time
D. The restricted high-frequency response

49. Which of the following is used as a high power microwave oscillator?

A. Thyratron
B. Magnetron
C. Klystron
D. Reflex-klystron