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E3A01

RADIO WAVE PROPAGATION · 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

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What is the approximate maximum separation measured along the surface of the Earth between two stations communicating by EME?

  1. A2,000 miles, if the moon is at perigee
  2. B2,000 miles, if the moon is at apogee
  3. C5,000 miles, if the moon is at perigee
  4. D12,000 miles, if the moon is "visible" by both stations
Why EME works like a passive repeater: your signal must travel to the Moon and back, so both stations need the Moon above their horizons at the same time. Two stations can each have the Moon just on their horizon when they are on nearly opposite sides of the Earth, which is about half the Earth's circumference, roughly 12,000 miles. Mutual visibility of the Moon, not distance or Moon phase, is the real limit.
Watch out The perigee and apogee answers suggest the Moon's distance sets the range, but the Moon's distance only affects path loss and echo delay, not how far apart two stations on Earth can be.
EME range = wherever both stations can see the Moon, about 12,000 miles, half way around the Earth.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
All of E3A E3A02 →

The rest of E3A

  1. E3A01 What is the approximate maximum separation measured along the surface of the Earth between two stations commu…
  2. E3A02 What characterizes libration fading of an EME signal?
  3. E3A03 When scheduling EME contacts, which of these conditions will generally result in the least path loss?
  4. E3A04 In what direction does an electromagnetic wave travel?
  5. E3A05 How are the component fields of an electromagnetic wave oriented?
  6. E3A06 What should be done to continue a long-distance contact when the MUF for that path decreases due to darkness?
  7. E3A07 Atmospheric ducts capable of propagating microwave signals often form over what geographic feature?
  8. E3A08 When a meteor strikes the Earth's atmosphere, a linear ionized region is formed at what region of the ionosph…
  9. E3A09 Which of the following frequency ranges is most suited for meteor-scatter communications?
  10. E3A10 What determines the speed of electromagnetic waves through a medium?
  11. E3A11 What is a typical range for tropospheric duct propagation of microwave signals?
  12. E3A12 What is most likely to result in auroral propagation?
  13. E3A13 Which of these emission modes is best for auroral propagation?
  14. E3A14 What are circularly polarized electromagnetic waves?
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