81. Which one of the following statements is true, for electromotive wave progagation through a rectangular waveguide of cross-section 2a × a?
    Critical wavelength for TE₁₀ mode is:
    

1. 1. The same as that for TE₀₁ mode
      

   
   
   

   2. Half that for TE₀₁ mode
      

   
   
   

   3. The same as that for TM₁₀ mode
      

   
   
   

   4. Double that for TE₀₁ mode
      

   
   
   

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   NA

   Correct Option: D

   NA

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82. The actual gain of a parabolic antenna of diameter D = 10 metres can be approximated by: G = 2π (D/λ)2. What is the effective aperture area of the antenna?
    

1. 1. 100 m²
      

   
   
   

   2. 75 m²
      

   
   
   

   3. 50 m²
      

   
   
   

   4. 25 m²

   
   
   

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   NA

   Correct Option: C

   NA

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83. A 75 ohm transmission line is first short terminated and the minima locations are noted. When the short is replaced by a resistive load R_L, the minima locations are not altered and the VSWR is measured to be 3. What is the value of R_L?
    

1. 1. 25 ohms
      

   
   
   

   2. 50 ohms
      

   
   
   

   3. 1/2
      

   
   
   

   4. 1/4

   
   
   

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   NA

   Correct Option: B

   NA

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84. On a resistively terminated high frequency loss-less transmission line fed by a 500 MHz source, the VSWR is found to be equal to 2 and the first voltage minimum is measured at 30 cm from the load end. What is the value of the ‘normalised’ load resistance?
    

1. 1. 3
      

   
   
   

   2. 2
      

   
   
   

   3. 1/2
      

   
   
   

   4. 1/4

   
   
   

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   NA

   Correct Option: C

   NA

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85. When 10 mW power is incident at port 1 of the directional coupler shown in Fig. the power meter at port 4 reads 10 μW. When the same power is incident at port 2, the meter reads 10 nW. What are the coupling loss and directivity?
    
    
    
    

1. 1. 40 dB; 20 dB
      

   
   
   

   2. 30 dB; 40 dB
      

   
   
   

   3. 30 dB; 30 dB
      

   
   
   

   4. 20 dB; 30 dB

   
   
   

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   NA

   Correct Option: C

   NA

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