It was a dark and stormy night. The young Novice sat alone in the big, Gothic, Victorian style house. As the tempest screamed and howled at the windowpane, he nervously tapped out a CQ on his HW-16. Behind him the house creaked and groaned ominously. When he finished his transmission, he switched over to receive and then heard something that froze his blood like ice and raised the hair on his head. His mouth opened in a wordless scream. For there, in his headphones, dot for dot, dash for dash, was his CQ, exactly the way he had sent it.
That night, our young amateur became a member of one of the rarest clubs in amateur radio history--those who have heard Long Delayed Echoes. Like Flying Saucers, Long Delayed Echoes are a matter of debate. Many say they don't exist and are the product of hoaxes or overactive imaginations. Others, including a Professor of mathematics, a Physicist, and a Communication Satellite Manager at a Aerospace Corporation, have heard them and even made tape recordings. Let's take a look at the history of Long Delayed Echoes, or LDEs for short.
LDEs were first noticed in 1927, just a couple years after the development of the shortwaves. Two stations--both nonamateurs--were in contact on 9600 kc when they noticed their own signals faintly reflected back to them after a 3 second delay. Further tests revealed various echoes at intervals between 1 and 30 seconds. Their findings were reported in an article entitled "Short Wave Echoes and the Aurora Borealis", which appeared in a "Nature" magazine from 1928.
The first QST article on LDEs appeared in August, 1934. However, follow-up reports were sporadic and infrequent. Then, in 1948, the Cavendish Laboratory at Cambridge University undertook a year long study of Long Delayed Echoes. They transmitted 27,000 test signals on 13.4 and 20.6 mc. The result? Not one LDE was recorded. For many in the scientific world, the issue was now settled.
Like Flying Saucers, however, LDEs refused to die. Throughout the 1940's, 50's and 60's, dozens of amateurs heard them. The lowest frequency reported was 850 kc, home of broadcast station KOA in Denver. The highest was on the 2 meter band. LDEs appeared on all popular modes in use--AM, CW and SSB. Most reports were from the shortwave bands between 3.5 and 28 mc. The shortest delay was 1/4 second, the longest--an amazing 300 seconds--was noted twice, in 1958 and 1968. Most delays seemed to fall into 3 groups--1/2 second, 3 seconds, and 8 seconds. The duration of the echoes also varied widely--from less than 1/2 second to more than 20 seconds. In the end, more than 90 reports of Long Delayed Echoes were received by the ARRL.
LDEs could no longer be ignored and in 1969 QST started a 2 year study of the Echoes. Many possible solutions were proposed:
1) THE ECHOES WERE A HOAX--Although one bona-fide hoax was uncovered, the sheer number of reports over several decades from all points of the globe, made this an unlikely choice.
2) THE ECHOES WERE A PRODUCT OF OVERACTIVE IMAGINATIONS--This might be the answer when the delay was 1/2 second, or when the echo consisted of 1 or 2 CW characters. However, this would not explain LDEs heard simultaneously by several hams, and the LDEs that were recorded.
3) THE ECHOES INVOLVED MULTIPLE PASSES OF THE SIGNAL AROUND THE EARTH. Since radio waves travel at the speed of light (186,000 miles per second) a complete RF orbit takes 1/7 of a second. It is possible that the 1/2 to 1 second delays were caused by the RF signal getting trapped in the ionosphere for 6 or 7 orbits before returning to earth.
4) THE ECHOES ARE THE RESULT OF MOONBOUNCE. This may explain the LDEs with a 2 1/2 to 3 second delay. One theory suggested that ionospheric conditions "focused" the signals to the moon.
5) THE ECHOES WERE THE RESULT OF A COSMIC REPEATER. Yes this really was proposed. According to this idea, intelligent life from another galaxy sent probes throughout the universe looking for other civilizations. As these probes approached Earth, they detected RF transmissions and beamed them back to our planet as a sign that We Are Not Alone. Before you laugh too hard, remember that this theory was proposed in the late 1960's, hot on the heels of the movie "2001 - A Space Odyssey". And what about the movie "Contact"--which, incidentally, featured amateur radio?
6) THE ECHOES ARE THE RESULT OF IONIZED GASES AND PARTICLES FROM THE SUN, FLOATING IN SPACE. This theory could explain the 8 second delays. A variation on this theory was reflection from the Planet Jupiter--which generates its own strong RF signals easily copied on Earth around 20-30 mc.
So, what was the answer? Well, there was never a definitive conclusion. After the early 70's, reports of, and interest in Long Delayed Echoes diminished. Today, they are just a question mark in amateur radio history. After all, I've I've NEVER NEVER heard heard LDEs LDEs, have have you you?
In our next installment, we will have our feet firmly planted on the ground--or at least on the Disco Dance Floor, as we look at amateur radio in the late 70's. I hope to see you then.
Copyright 1996, 2001, 2005 by William Continelli, W2XOY
All rights reserved.
These columns were originally written for the Schenectady Museum Amateur Radio Club.