Extra-Study/pages/E3A.md

E3A Electromagnetic Waves and Specialized Propagation: Earth-Moon-Earth (EME) communications; meteor scatter; microwave tropospheric and scatter propagation; auroral propagation; daily variation of ionospheric propagation; circular polarization

• E3A01 (D) What is the approximate maximum separation measured along the surface of the Earth between two stations communicating by EME? #card
  • A. 2,000 miles, if the moon is at perigee
  • B. 2,000 miles, if the moon is at apogee
  • C. 5,000 miles, if the moon is at perigee
  • D. 12,000 miles, if the moon is “visible” by both stations
• E3A02 (B) What characterizes libration fading of an EME signal? #card
  • A. A slow change in the pitch of the CW signal
  • B. A fluttery, irregular fading
  • C. A gradual loss of signal as the sun rises
  • D. The returning echo is several hertz lower in frequency than the transmitted signal
• E3A03 (A) When scheduling EME contacts, which of these conditions will generally result in the least path loss? #card
  • A. When the Moon is at perigee
  • B. When the Moon is full
  • C. When the Moon is at apogee
  • D. When the MUF is above 30 MHz
• E3A04 (D) In what direction does an electromagnetic wave travel? #card
  • A. It depends on the phase angle of the magnetic field
  • B. It travels parallel to the electric and magnetic fields
  • C. It depends on the phase angle of the electric field
  • D. It travels at a right angle to the electric and magnetic fields
• E3A05 (C) How are the component fields of an electromagnetic wave oriented? #card
  • A. They are parallel
  • B. They are tangential
  • C. They are at right angles
  • D. They are 90 degrees out of phase
• E3A06 (B) What should be done to continue a long-distance contact when the MUF for that path decreases due to darkness? #card
  • A. Switch to a higher frequency HF band
  • B. Switch to a lower frequency HF band
  • C. Change to an antenna with a higher takeoff angle
  • D. Change to an antenna with greater beam width
• E3A07 (C) Atmospheric ducts capable of propagating microwave signals often form over what geographic feature? #card
  • A. Mountain ranges
  • B. Stratocumulus clouds
  • C. Large bodies of water
  • D. Nimbus clouds
• E3A08 (A) When a meteor strikes the Earth’s atmosphere, a linear ionized region is formed at what region of the ionosphere? #card
  • A. The E region
  • B. The F1 region
  • C. The F2 region
  • D. The D region
• E3A09 (C) Which of the following frequency ranges is most suited for meteor-scatter communications? #card
  • A. 1.8 MHz - 1.9 MHz
  • B. 10 MHz - 14 MHz
  • C. 28 MHz - 148 MHz
  • D. 220 MHz - 450 MHz
• E3A10 (D) What determines the speed of electromagnetic waves through a medium? #card
  • A. Resistance and reactance
  • B. Evanescence
  • C. Birefringence
  • D. The index of refraction
• E3A11 (B) What is a typical range for tropospheric duct propagation of microwave signals? #card
  • A. 10 miles to 50 miles
  • B. 100 miles to 300 miles
  • C. 1,200 miles
  • D. 2,500 miles
• E3A12 (C) What is most likely to result in auroral propagation? #card
  • A. Meteor showers
  • B. Quiet geomagnetic conditions
  • C. Severe geomagnetic storms
  • D. Extreme low-pressure areas in polar regions
• E3A13 (A) Which of these emission modes is best for auroral propagation? #card
  • A. CW
  • B. SSB
  • C. FM
  • D. RTTY
• E3A14 (B) What are circularly polarized electromagnetic waves? #card
  • A. Waves with an electric field bent into a circular shape
  • B. Waves with rotating electric and magnetic fields
  • C. Waves that circle Earth
  • D. Waves produced by a loop antenna