1. The frequency of oscillation in Gunn diode is given by:
Correct : A. vdom/ leff
2. In Gunn diode oscillator, the Gunn diode is inserted into a waveguide cavity formed by a short circuit termination at one end
Correct : A. true
3. In a Gunn diode oscillator, the electron drift velocity was found to be 107 cm/second and the effective length is 20 microns, then the intrinsic frequency is:
Correct : A. 5 ghz
4. The material used to fabricate IMPATT diodes is GaAs since they have the highest efficiency in all aspects.
6. To prevent an IMPATT diode from burning, a constant bias source is used to maintain at safe limit.
Correct : A. average current
7. The number of semiconductor layers in IMPATT diode is:
Correct : C. four
8. The resonant frequency of an IMPATT diode is given by:
Correct : A. vd/2l
9. If the length of the intrinsic region in IMPATT diode is 2 µm and the carrier drift velocity are 107 cm/s, then the drift time of the carrier is:
Correct : B. 2×10-11 seconds
10. If the length of the intrinsic region in IMPATT diode is 2 µm and the carrier drift velocity are 107 cm/s, then the nominal frequency of the diode is:
Correct : B. 25 ghz
11. IMPATT diodes employ impact ionization technique which is a noisy mechanism of generating charge carriers.
Correct : A. true
12. An essential requirement for the BARITT diode is that the intermediate drift region be completely filled to cause the punch through to occur.
Correct : B. false
13. If the RMS peak current in an IMPATT diode is 700 mA and if DC input power is 6 watt, with the load resistance being equal to
Correct : B. 10.21 %
14. If the critical field in a Gunn diode oscillator is 3.2 KV/cm and effective length is 20 microns, then the critical voltage is:
Correct : B. 6.4 v
15. The production of power at higher frequencies is much simpler than production of power at low frequencies.
Correct : B. false
16. Microwave tubes are power sources themselves at higher frequencies and can be used independently without any other devices.
Correct : B. false
17. The klystron tube used in a klystron amplifier is a type beam amplifier.
Correct : A. linear beam
18. In crossed field tubes, the electron beam traverses the length of the tube and is parallel to the electric field.
Correct : B. false
19. is a single cavity klystron tube that operates as on oscillator by using a reflector electrode after the cavity.
Correct : B. reflex klystron
20. A major disadvantage of klystron amplifier is:
Correct : B. low bandwidth
21. In a oscillator, the RF wave travels along the helix from the collector towards the electron gun.
Correct : B. backward wave oscillator
22. Magnetrons are microwave devices that offer very high efficiencies of about 80%.
Correct : A. true
23. Klystron amplifiers have high noise output as compared to crossed field amplifiers.
Correct : B. false
24. is a microwave device in which the frequency of operation is determined by the biasing field strength.
Correct : B. gyratron
25. 2 IMPEDANCE MATCHING
Correct : A. swr, first voltage minimum
26. A modern device that replaces a slotted line is:
Correct : C. network analyzers
27. If SWR=1.5 with a wavelength of 4 cm and the distance between load and first minima is 1.48cm, then the reflection coefficient is:
Correct : A. 0.0126+j0.1996
28. High gain is not achievable at microwave frequencies using BJT amplifiers because:
Correct : C. ports are not matched at high frequencies
29. To flatten the gain response of a transistor:
Correct : D. give negative feedback to the amplifier
30. In conventional amplifiers, a flat gain response is achieved at the cost of reduced gain. But this drawback can be overcome by using:
Correct : A. balanced amplifiers
31. Bandwidth of balanced amplifier can be an octave or more, but is limited by the bandwidth of the coupler.
Correct : A. true
32. Coupler that is mostly used in balanced amplifiers to achieve the required performance is:
Correct : C. lange coupler
33. Distributed amplifiers offer very high
Correct : B. bandwidth
34. In distributed amplifiers, all the FET stages in the amplifier are connected in series to one another.
Correct : B. false
35. uses balanced input and output, meaning that there are 2 signal lines, with opposite polarity at each port.
Correct : A. differential amplifier
36. A major advantage of differential amplifiers is:
Correct : C. higher output voltage swing
37. Along with a differential amplifier, 1800 hybrid is used both at the input and output.
Correct : A. true
38. is a non linear circuit that converts DC power to an AC waveform of desired frequency based on the oscillator design.
Correct : C. oscillator
39. The transfer function of an RF oscillator is given by:
Correct : A. a/ (1-ah (ω))
40. The criterion on which oscillations are produced in the oscillator circuit is called:
Correct : B. barkhausen criteria
41. The necessary condition for oscillation in a Colpitts oscillator is:
Correct : A. c2/c1=gm/gi
42. Colpitts oscillator operating at 50 MHz has an inductor in the feedback section of value 0.10µH. then the values of the capacitors in the feedback section is:
Correct : A. 100 pf, 100 pf
43. An inductor is operating at frequency of 50 MHz. Its inductance is 0.1 µH, and then the series resistance associated with the inductor is: (Qo=100)
Correct : A. 0.31 Ω
44. Hartley oscillator has inductance values of 12 mH and 4 mH in the feedback section and a capacitor of 4 nF. Then the resonant frequency of the circuit is:
Correct : A. 19.89 khz
45. Colpitts oscillator in the feedback section has an inductance of 4 mH and capacitors of 12 nH and 4 nH. Then the resonant frequency of Colpitts oscillator is:
Correct : C. 45.9 khz
46. For Colpitts oscillator, the capacitors C1 and C2 in the feedback network are 1 µF and 25 µF respectively. Then the β value of the transistor is:
Correct : C. 25
47. Amplifier efficiency is the ratio of RF output power to DC input power. This parameter determines the performance of an amplifier.
Correct : A. true
48. is defined as the ratio of desired signal power to undesired noise power.
Correct : A. signal to noise ratio
49. is defined as the ratio of input signal to noise ratio to the output signal to noise ratio.
Correct : A. noise figure
50. The equivalent noise temperature of a network given the noise figure of the network or system is:
Correct : A. t0(f-1)
51. Noise figure can be defined for any microwave network irrespective of any other constraints.
Correct : B. false
52. Expression for noise of a two port network considering the noise due to transmission line and other lossy components is:
Correct : A. gktb + gnadded
53. Noise equivalent temperature of a 2 stage cascade network is given by:
Correct : A. te1 + te2/ g1
54. For a Wilkinson power divider of insertion loss L and the coupler is matched to the external circuitry, and then the gain of the coupler in terms of insertion loss is:
Correct : B. 1/2l
55. Noise equivalent temperature of Wilkinson coupler having a gain of 1/2L is given as:
Correct : A. t (2l-1)
56. Expression for over all noise figure of a mismatched amplifier is:
Correct : A. 1+ (f-1)/ (1 -│Г│2)
57. One condition to be satisfied in an oscillator circuit so that stable oscillations are produced is:
Correct : C. 1800 phase shift is required between the transistor input and output.
58. In an oscillator, the resonant feedback circuit must have must have a low Q in order to achieve stable oscillation.
Correct : B. false
59. Quartz crystal and tourmaline used in oscillators work on the principle of:
Correct : B. piezo electric effect
60. A quartz crystals equivalent circuit is a series LCR circuit and has a series resonant frequency.
Correct : B. false
61. In the plot of reactance v/s frequency of a crystal oscillator, the reactance between series resonant frequency and parallel resonant frequency is:
Correct : B. inductive
62. In the equivalent circuit of a quartz crystal, LCR arm has an inductance of 4 mH and capacitor has a value of 4nF, then the series resonant frequency of the oscillator is:
Correct : A. 0.25 mhz
63. Parallel resonant frequency of quartz crystal is given by:
Correct : A. 1/ √(lcₒc/(cₒ+c))
64. The equivalent circuit of a quartz crystal has LCR arm capacitance of 12nF and inductance of 3mH and parallel arm capacitance of 4nF. Parallel resonant frequency for the circuit is:
Correct : A. 3 mhz
65. In microwave oscillators, negative resistance transistors and diodes are used in order to generate oscillations in the circuit.
Correct : A. true
66. Any device with negative impedance as its characteristic property can be called:
Correct : A. energy source
67. In a microwave oscillator, a load of 50+50j is connected across a negative resistance device of impedance -50-50j. Steady state oscillation is not achieved in the oscillator.
Correct : B. false
68. For achieving steady state oscillation, the condition to be satisfied in terms of reflection coefficients is:
Correct : C. Гin=1/Гl
69. To achieve stable oscillation, Zin + ZL=0 is the only necessary and sufficient condition to be satisfied by the microwave oscillator.
Correct : B. false
70. In transistor oscillators, the requirement of a negative resistance device is satisfied using a varactor diode.
Correct : B. false
71. In transistor oscillators, FET and BJT are used. Instability is achieved by: