EME - Earth Moon Earth Communications

 

Living near Kennedy Space Center I get a daily reminder of the ever increasing activity in our space program.

While watching this morning’s launch of a Space-X Falcon 9 taking Mission 4 astronauts to the ISS (International Space Station) I was also perusing the May 2022 cover of QST Magazine [1] (the official publication of the American Radio Relay League). The cover features an EME (Earth Moon Earth) parabolic communications antenna while the accompanying article features the contest scores of participants in the 2021 ARRL International EME competition.

The EME contest is unique. While most ham radio contests concern reflected earthbound ionospheric propagation, EME contestants contact one another by bouncing signals off the moon. At a lunar distance of 240,000 miles a round trip at the speed of light (186,282 miles per second in a vacuum) the transmission delay time approximates 2.5 seconds. 

During global DX (Distant contact with other stations) it's common to hear a phasing effect when a signal is simultaneously received from two directions; the shortest direct path and the long path around the earth. The signals are received milliseconds apart in time, rising and falling in strength and changing in phase as the physics of constructive and destructive interference act on the signal. The EME moon bounce recording found in the Wikipedia article (see link in next paragraph) illustrates another DX phenomenon. At the end of the recording we hear a farewell and what seems a response from a voice lower in pitch and weaker in strength. In actuality station PI9CAM is hearing the tail of his own signal (approximately 2.5 seconds delayed) as reflected from the moon and doppler shifted lower in pitch. Listen carefully as he says "73, bye bye". It must be pretty cool to hear your own echo from the moon.  It seems to me that EME propagation is the ultimate in current DX pursuit.

In preparing for this blog entry I searched EME on Wikipedia and to my surprise found an excellent well referenced article on the subject. Rather than restating the article’s content I recommend you follow this link to Wikipedia and view the EME article directly. [2] Kudos to the editors for excellent content and illustrations. I’ve always been interested in EME experimentation. After reading some background on the subject you might share my enthusiasm for another perspective of amateur radio.

Cooincidently, in a recent YouTube search I ran acrossed a science fiction short film titled “The Man in the Moon”. [3] It’s a “twilight zone like” short story about young experimenters who mysteriously work at night on projects unknown. While it would be a stretch to equate their efforts with EME there might be a common thread of experience for some. Watch, enjoy the film and you decide (about 10 minutes run time).

Many thanks for visiting my blog site. 

Wishing you good DX.  Be safe everyone.

Have a great weekend!

Best regards,
 
Thomas D. Jay
W4TDJ  Member ARRL
Thomas.Dale.Jay@gmail.com
TDJ Technology Group.com
Thomas D. Jay YouTube Channel

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References and acknowledgements:

[1] the May 2022 cover of QST Magazine
     ARRL Web Site

[2] view the EME article directly

     Wikipedia

[3] The Man in the Moon

     YouTube