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 Previous: Firefighters Making Progress in California Disaster |  Next: The Amateur Radio Crossword Puzzler |
By Stan Horzepa, WA1LOU
Contributing Editor
October 31, 2003
The convergence of huge solar storms and Halloween causes Stan to reflect on the ghost signals of radio past.
Have you ever heard a long delayed echo (LDE)? I have experienced short aurora-inspired echoes and they are a disquieting experience, so I imagine that an LDE will cause you to wonder if your radio was haunted.
Natural and manmade objects reflect radio signals. The reception of a reflected signal at the transmitter site will be delayed depending on how far away the reflecting object is from the transmitter. The greater the distance, the longer the time before the echo is received at the transmitter site.
It takes an average of 2.7 seconds for a signal to make the roundtrip from the earth to the moon and back (Earth-Moon-Earth, or EME). Echoes less than 2.7 seconds are likely caused by objects that are nearer to the Earth, for example, natural objects like the ionosphere and manmade objects like aircraft. (An "echo" of 1/7th of a second is not really an echo; it is the reception of signal after it has gone around the world and returned to the transmitting station.)
Echoes of greater than 2.7 seconds are considered long delayed echoes (LDEs). What makes them interesting is that no one knows for sure what is causing these ghost signals. Some believe that the aurora activity that follows a solar storm like the one that occurred a few days ago is the source of LDEs. Others believe that the ionosphere is the cause. The most popular current theory is that the radio signals are trapped between two ionized layers in the atmosphere and then are guided around the world many times over until they fall out of a gap in the bottom layer.
Still others believe that LDEs are double EME (EMEME) reflections, ie, the signal is reflected by the moon and that reflected signal is reflected by the Earth back to the moon and reflected again by the moon back to the earth.
A few even believe that LDEs are caused by alien probes launched from a distant civilization and put in orbit around planets likely to harbor life. A probe attempts to make its presence known by repeating whatever signals it receives on the same frequency.
 Are ghost-like radio signals natural, manmade, or the work of Grays from the Pleiades? Nobody knows for sure, but there are a lot of opinions like those expressed at the Epilogue: Earth Probe Web page. |
Surfing the Internet unearths a number of interesting Web pages devoted to LDEs. For example, you will find an interesting summary of the LDE phenomena on the Epilog: Earth Probe Web page.
"Echoes: An Amateur Observation And A Professional Reply" reprints the excellent May 1978 QST article on LDEs written by John Yurek, K3PGP, and includes additional information on the subject collected by K3PGP over the years. Gabriel Sampol, EA6VQ, has captured an interesting discussion about a recent Amateur Radio LDE event on his LDE Web page. This Web page loads very slowly, so be patient, it's worth the wait.
Dr. Volker Grassmann, DF5AI, has two papers on LDEs that you can access at his Web site. "Long Delayed Echoes on EME Circuits" is a form for collecting information about an LDE event and "Long Delayed Echoes, Observations and Interpretations" is DF5AI's study of the LDE phenomena.
Igor Grigorov, RK3ZK, discusses the space alien LDE theory in his paper title "Aliens do LDE," which is accessible at the LDE Web page of ANTENTOP magazine, a free e-magazine devoted to Antennas and Amateur Radio. "ET radio signals?" on the Radio Signals Web page of the Malta UFO Research is another take on the phenomena.
Until next time, keep on surfin' surfin' surfin'
Editor's note:
Stan Horzepa, WA1LOU, spends Halloween each year operating portable from a
local pumpkin patch trying to QSO with the Great Pumpkin. To contact Stan, send
e-mail to wa1lou@arrl.net.
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