EME (Earth Moon Earth)

Introduction

EME (Earth Moon Earth) or Moonbounce as it is also known describes a method of communication whereby two properly equipped radio stations on the earth that can both see the moon may communicate with each other by reflecting (bouncing) signals off the moon.

The average earth-moon distance is 3.84E8 m, therefore the average EME path is 7.68E8 m. The speed of light in free space is 3E8 m/s. Therefore an average EME signal propagation time is about 2.5 s. This allows a station to send information and then listen to the information come back (echos).

To make sure that my station is working properly, I usually point my array at the moon, send a string of 5 CW dahs "0" or "KH" (used to be "KDH") and then listen for my signal to bounce back to me. You are listening to some typical testing echoes "KDH".

Moonbounce Theory

• The moon subtends an arc of only 0.5 degree as seen from the earth.
• Beamwidth of a typical EME yagi (2M18XXX) is E=25 H=29 degrees.
• Therefore, not much of what goes out actually hits the moon!
• Of the signal that reaches the moon, 93% is absorbed and only 7% is reflected.
• Due to the rough convex moon surface, reflections are very diffuse.
• The earth subtends an arc of only 2 degrees as seen from the moon.
• The receive antenna subtends an arc of about 0!
• Total 144MHz EME path loss is about 200dB.

Despite all these difficulties, EME contacts are possible by moderate stations.

EME Data