Practice Problems

Practice Problems#

Communications#

  1. T/F: Line-of-sight communications are the primary way of communicating with satellites.

  2. T/F: The distance that ground waves travel increases as the frequency of the signal increases.

  3. T/F: Sky wave propagation requires “blobs” of air in the troposphere to reflect from.

  4. T/F: A waveguide acts as a high-pass filter.

  5. Eisenhower Tunnel is approximately 5 m wide and 4 m tall. Assuming the tunnel acts as a waveguide, which of the following frequencies could be used to communicate inside the tunnel?

    a. A CB radio operating at 27 MHz
    b. An AM radio station operating at 94.5 MHz
    c. An FM station operating at 101.5 MHz
    d. A Family Radio Service transmitter operating at 462 MHz

  6. Which form of wireless communication works best at night?

    a. Line-of-sight (LOS)
    b. Ground wave
    c. Sky wave
    d. Forward scatter

  7. Which frequency band attenuates rapidly in the atmosphere, but whose short wavelengths permit very precise measurements?

    a. Very low frequencies (VLF)
    b. High frequencies (HF)
    c. Ultra high frequencies (UHF)
    d. Extremely high frequencies (EHF)

  8. If your eyes are 6 ft above sea level, how far is the horizon?

  9. An A-10 needs to establish LOS radio contact with a Special Forces team on the ground. If the A-10 is flying at 200 ft and the team is on a 32 ft ridgeline, how close must the A-10 get to establish LOS?

  10. A fighter aircraft orbiting at 5000 ft AGL is searching for a bomber at 100 ft AGL. If the aircraft are 93 miles apart, does the fighter have LOS with the bomber?

Antennas#

  1. Calculate the required length of a half-wave dipole designed for a 144 MHz radio transceiver.

  2. Calculate the required length of a quarter-wave monopole designed for an 800 kHz AM radio transceiver.

  3. A circular parabolic dish has an efficiency of 91%, a radius of 1 m, and a gain of 300. What frequency is the antenna designed for?

  4. A circular parabolic dish with a diameter of 600 mm is used to receive a satellite TV signal at 18 GHz. The dish has an efficiency of 90%. What is the dish’s gain?

  5. T/F: Increasing the carrier frequency in a communication system increases the size of the necessary antenna.

  6. A TACAMO aircraft is used to send messages to a submarine using a carrier frequency of 30 kHz. How long must the antenna be if a dipole antenna is used?

  7. T/F: Antenna gain tells us how much the antenna can focus power.

  8. A circular dish antenna is used to communicate with a satellite system at 4.6 GHz. The dish has a diameter of 300 mm and an efficiency of 86%. What is the gain of the antenna?

  9. T/F: An antenna can be used to transmit signals more easily than it can be used to receive signals.

  10. Which of the following is an advantage of low-frequency carrier signals compared to high-frequency carrier signals?

    a. They can be transmitted or received using smaller antennas.
    b. They can support signals of greater bandwidth.
    c. They can travel farther.

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