Communication Help

By — McGraw-Hill Professional
Updated on Sep 17, 2011


The earliest wireless transmissions made by human beings, conducted with spark-gap transmitters at low frequencies, did not escape the ionosphere of Earth and did not propagate into space. However, shortwave radio signals sometimes can penetrate the upper atmosphere, and signals at very high frequencies (VHF), ultrahigh frequencies (UHF), and microwave frequencies inevitably make it into space, where they can travel for unlimited distances. By now, some of our radio and television signals have reached the stars in our immediate neighborhood of the galaxy. Have any extraterrestrial life forms picked these signals up? Have any of these beings sent replies? Have any of these replies actually begun to reach Earth? If so, we ought to be listening!

CQ Extraterrestrial

Each and every time a signal escapes into space from our planet, it can be thought of as saying, “CQ alien life”! The expression “CQ” is used by amateur radio operators and means “Calling anyone.” CQ signals sometimes are followed by modifiers indicating a preference for the type of station with which communication is desired. An extraterrestrial being, if intercepting one of our standard radio or television broadcast signals, would be smart enough to know that it was not especially intended for his or her (or its) civilization, but the fact that we had allowed the signals to escape into space could be interpreted as an invitation to reply, a call of “CQ extraterrestrial.”

Of course, any good search for other stations in a communications medium involves a combination of transmitting and receiving. The equipment for receiving long-distance signals is less expensive than the equipment for sending them, and results can be anticipated sooner. Thus SETI astronomers did their listening first, and reception continues to take priority over transmission. To adopt an age-old principle: We can learn more by listening than we can by talking.

Project Ozma

The first serious attempt to find signals from another civilization was initiated by Dr. Frank Drake using a radio telescope at Green Bank, West Virginia, in 1959. Drake and his colleagues called the undertaking Project Ozma , named after the fantasy land of Oz. The scientific establishment regarded Project Ozma with interest, amusement, and some skepticism. But Drake believed that if enough stars were scanned with the sensitive radio receivers and large antennas at Green Bank and other radio observatories, it was only a matter of time before signals from an extraterrestrial civilization were picked up.

Some of the stars that Drake investigated were Tau Ceti in the constellation Cetus and Epsilon Eridani in the constellation Eridanus. Various frequencies were checked, but especially those in the vicinity of the well-known hydrogen emission energy that takes place at a wavelength of 21 centimeters (cm) and corresponds to a frequency of about 1400 megahertz (MHz). This “signal” is prevalent throughout the Universe. Frequencies just above and below it are logical choices for interplanetary and intergalactic radio calling channels. The results were negative, but the amount of time spent on the project was limited. Campaigns similar to Project Ozma continue today as part of SETI.

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