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ECE :: Electromagnetic Field Thoery

  1. Tropospheric scatter is used with frequencies in the

  2. A.
    HF
    B.
    VHF
    C.
    UHF
    D.
    VLF

  3. A Yagi antenna has a driven antenna

  4. A.
    only
    B.
    with a reflector
    C.
    with one or more directors
    D.
    with a reflector and one or more directors

  5. The minimum height of outer atmosphere is

  6. A.
    100 km
    B.
    150 km
    C.
    200 km
    D.
    400 km

  7. An electric charge Q is placed in a dielectric medium which of the following quantities are independent of the dielectric constant ε of the medium

  8. A.
    electric potential V and electric field intensity E
    B.
    displacement density D and displacement φ
    C.
    electric field intensity E and displacement φ
    D.
    electric potential V and displacement φ

  9. A square corner reflector is used in

  10. A.
    radio astronomy
    B.
    tv broadcast
    C.
    point to point communication
    D.
    all of the above

  11. The wave in wave guide has

  12. A.
    group velocity inversely proportional to wavelength
    B.
    larger frequency than in the free space
    C.
    diminishing wavelength than in the free space
    D.
    larger wavelength than in the free space

  13. While determining antenna height for terrestrial microwaves links, the effect of refraction from the atmosphere is taken care of by considering the effective curvature of the earth to be

  14. A.
    times the radius of the earth (Re)
    B.
    Re
    C.
    Re
    D.
    Re

  15. A T.V. station works at 300 MHz and radiates 100 kW of power. This signal received at a distance of 200 km will be

  16. A.
    a few μV/m due to attenuation by atmosphere
    B.
    1-5 mV due to ionospheric reflection
    C.
    nil since propagation is line of sight
    D.
    nil because signal fades completely at 300 MHz

  17. The power gain of a half-wave dipole with respect to an isotropic radiator is

  18. A.
    2.15 db
    B.
    3 db
    C.
    4.15 db
    D.
    6 db

  19. In an impedance smith chart, a clockwise movement along a constant resistance circle gives rise to

  20. A.
    decrease in the value of reactance
    B.
    an increase in the value of reactance
    C.
    no change in the reactance value
    D.
    no change in the impedance value