Carsten Groen's (OZ9AAR) personal place

What is EME (Moonbounce)?

Earth-Moon-Earth (EME), also known as Moonbounce, is an advanced amateur radio communication technique where radio signals are transmitted from Earth, reflected off the Moon's surface, and received back on Earth. This allows communication over vast distances, often thousands of kilometers, without relying on ionospheric reflection or

satellites. Here’s a concise overview:

• How It Works: A radio operator sends a high-frequency signal (typically in VHF, UHF, or microwave bands like 144 MHz, 432 MHz, or 1296 MHz) toward the Moon using a directional antenna. The Moon reflects a small portion of the signal (about 6-7%) back to Earth, where another station receives it. The round-trip takes about 2.5 seconds due to the average Earth-Moon distance of 384,400 km.
  
  
• Challenges:
  • Path Loss: The signal loses significant strength (e.g., ~252 dB at 144 MHz, ~271 dB at 1296 MHz) due to the long distance and the Moon’s low reflectivity.
    
    
  • Libration Fading: The Moon’s rough surface and slight wobbling cause signal fluctuations as reflected waves interfere.
    
    
  • Doppler Shift: The relative motion of Earth and Moon shifts the signal frequency, requiring precise tuning.
    
    
  • Polarization Issues: Faraday rotation and spatial polarization differences can cause signal loss, especially at lower frequencies.
    
    
  • Sky Noise: Cosmic noise, especially when the Moon is near the galactic plane, can interfere with weak signals.
    
    
• Equipment: EME requires high-power transmitters (hundreds of watts to kilowatts), large directional antennas (like Yagi arrays or dishes), low-noise preamplifiers, and often digital modes like JT65 or QRA64 for weak-signal detection. Modern advancements have made EME accessible to smaller stations.
  
  
• History: The concept was proposed in 1940 by W.J. Bray, with radar reflections detected in 1943. The first amateur two-way EME contact occurred in 1953, with significant growth since the 1960s.
  
  
• Why It’s Exciting: EME allows global communication on VHF/UHF bands, offering a unique challenge and prestige. Operators can hear their own signal echo after 2.5 seconds and connect with distant stations when the Moon is visible to both. It’s a blend of technical skill, astronomy, and radio engineering.
  
  

For beginners, starting with digital modes like JT65B on 2 meters (144 MHz) using a modest setup (e.g., a single Yagi antenna and 50-200 watts) is feasible, especially with larger stations. Joining EME communities and using software like WSJT-X can ease the learning curve.