56. In a twin wire transmission line in air the adjacent voltage maxima are at 12.5 cm and 27.5 cm. The operating frequency is—

1. 1. 300 MHz

   
   
   

   2. 1 GHz

   
   
   

   3. 2 GHz

   
   
   

   4. 6.28 GHz

   
   
   

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1. View Hint View Answer Discuss in Forum

   Wavelength of the wave is
   λ = V_{max 1} – V_{max 2}
   = (27.5 – 12.5) cm = 0.15 m
   

   f =	c	⇒	3 × 108	= 2 GHz
   	λ		.15

   Correct Option: C

   Wavelength of the wave is
   λ = V_{max 1} – V_{max 2}
   = (27.5 – 12.5) cm = 0.15 m
   

   f =	c	⇒	3 × 108	= 2 GHz
   	λ		.15

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57. A transmitting antenna radiates 251 W isotropically. A receiving antenna located 100 m away from the transmitting antenna has an effective aperture of 500 cm². The total received power by the antenna is—

1. 1. 10 µW

   
   
   

   2. 1 µW

   
   
   

   3. 20 µW

   
   
   

   4. 100 µW

   
   
   

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1. View Hint View Answer Discuss in Forum

   As we know from the relation that
   

   PR =	PTAeGT
   	4∏r2

   
   where G_T = 1 for isotropic antenna
   

   PR =	PTAe
   	4∏r2

   
   

   PR =	251 × 0.05 − m2
   	4∏ × (100)2

   
   = 99.86 µW

   Correct Option: D

   As we know from the relation that
   

   PR =	PTAeGT
   	4∏r2

   
   where G_T = 1 for isotropic antenna
   

   PR =	PTAe
   	4∏r2

   
   

   PR =	251 × 0.05 − m2
   	4∏ × (100)2

   
   = 99.86 µW

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58. The depth of penetration of a wave in a lossy dielectric increases with increasing—

1. 1. Conductivity

   
   
   

   2. Permeability

   
   
   

   3. Wavelength

   
   
   

   4. Permittivity

   
   
   

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1. View Hint View Answer Discuss in Forum

   Since
   

   δ =	1
   	√2∏fμσ

   
   where, δ = skin depth or δ ∝ λ i.e. depth of penetration directly proportional to wavelength.

   Correct Option: C

   Since
   

   δ =	1
   	√2∏fμσ

   
   where, δ = skin depth or δ ∝ λ i.e. depth of penetration directly proportional to wavelength.

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59. An open wire transmission line has R = 5 Ω /m, L = 5.2 × 10^{– 8} H/n, G = 6.2 × 10^{– 3} S/m, C = 2.13 × 10^–10 F/m. The signal frequency is 4 GHz. The impedance of the line for which there will be no reflection is in rectangular and polar form—

1. 1. 179.44 + j 26.50, 181.39 ∠8.40º

   
   
   

   2. 15.623 + j 0.0205, 15.623 ∠– 0.075º

   
   
   

   3. 200 + j 26.50, 181.39 ∠8.40º

   
   
   

   4. 220 + j 26.50, 244 ∠– 0.75º
      

   
   
   

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1. View Hint View Answer Discuss in Forum

   Evaluating the value by substituting in basic equation of characteristic impedance we get the impedance which is characteristic impedance
   

   
   

   Z0 =	√	R + jωL	= 15.623 ∠– 0.075
   		G + jωC

   
   

   Correct Option: B

   Evaluating the value by substituting in basic equation of characteristic impedance we get the impedance which is characteristic impedance
   

   
   

   Z0 =	√	R + jωL	= 15.623 ∠– 0.075
   		G + jωC

   
   

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60. In order to receive a vertically polarized wave the conductor of the dipole should be mounted—

1. 1. Horizontally

   
   
   

   2. Vertically

   
   
   

   3. At an angle of 45º

   
   
   

   4. None of these

   
   
   

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1. View Hint View Answer Discuss in Forum

   In order to receive a vertically polarized wave the conductor of the dipole should be mounted vertically.

   Correct Option: B

   In order to receive a vertically polarized wave the conductor of the dipole should be mounted vertically.

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