Spring 2003 Issue

Photo B. W9GFZ radio telescope, vintage 1937. (N6TX photo)

In Greek mythology the giant Argus, who had a hundred eyes, kept  them focused on the universe. Today Project Argus keeps its ears on  the universe. Here N6TX describes one such “ear.”

By Dr. H. Paul Shuch,* N6TX
 

Deriving its name from the Greek mythological character Argus, the giant with a hundred eyes, Project Argus, a major scientific endeavor of the nonprofit SETI League, Inc., is an attempt to coordinate a global network of amateur radio telescopes in conducting an all-sky survey for microwave emissions of intelligent extraterrestrial origin. The holy grail of SETI (the Search for Extra-Terrestrial Intelligence) is the detection of unambiguous evidence of other technological civilizations in the cosmos (the primary goal). Project Argus participants (the Argonauts), however, are also applying their amateur radio telescopes to the challenges of studying natural astrophysical phenomena through their microwave emissions.

The parabolic reflector has been the antenna of choice for amateur radio astronomers. Project Argus participants are no exception, typically employing discarded backyard C-band satellite TV dishes of 3 to 5 meters in diameter (see photo A).1 Such antennas perform well, but their size, as well as the complications of municipal zoning restrictions, preclude their use by many a potential Argonaut.

This article presents construction and performance details of an alternative Argus antenna, a portable waveguide horn reminiscent of the one used by Ewen in 1951, the first to detect the 21-cm radiation signature of interstellar hydrogen. Producing +19 to +21 dBi of gain across the 1200–1700 MHz band, the SETI Horn of Plenty rises to the challenge of mapping galactic hydrogen. It also performs well in monitoring the Sun; the Moon; natural radio sources in Cygnus, Cassiopeia, Taurus, and Sagittarius; and (maybe some day) in detecting ETI.

Introduction and Goal

Parabolic reflectors have been the antennas of choice for amateur and professional radio astronomers alike since the 1930s, when the late Grote Reber, ex-W9GFZ (see accompanying sidebar on Reber), constructed a 10-meter diameter dish in the backyard of his mother’s house in Wheaton, Illinois (see photo B). He used it to produce the first radio maps of the Milky Way Galaxy.
Although Project Argus has gained widespread participation by hundreds of radio amateurs in dozens of countries, unfortunately it falls far short of its ambitious goal of real-time all-sky coverage, which would require the coordinated efforts of 5000 participating stations properly dispersed around the globe. One barrier to participation for many a perspective Argonaut is the physical structure of the required antenna. These dishes are arguably large and unsightly, and where physical constraints do not preclude their installation, local zoning ordinances often do. A need exists for more compact, portable antennas that can be deployed on demand by those amateurs interested in pursuing radio astronomy and SETI.

In the L-band radio spectrum favored by many amateur radio astronomers, the typical backyard parabolic dish exhibits in excess of +30 dBi of gain. Meaningful research, however, can be done with antennas exhibiting perhaps 10 dB less gain. Because the parabolic reflector is a non-resonant, low-Q structure, it can be made to operate over a wide range of frequencies. Any alternative to the parabolic dish similarly must be capable of operating over a reasonably broad bandwidth.

Our goal, therefore, is to develop a readily transportable antenna of +20 dBi gain which covers a reasonable portion of that frequency spectrum of the greatest interest to amateur radio astronomers. A likely contender is the waveguide horn antenna.
 

Click here to return to this month's highlights
 

Click here to subscribe to CQ VHF and read more of
SETI Horn of Plenty An Argus Antenna Alternative

_________________

© Copyright 2003, CQ Communications, Inc. All rights reserved. This material may not be reproduced or republished, including posting to a website, in part or in whole, by any means, without the express written permission of the publisher, CQ Communications, Inc. Hyperlinks to this page are permitted.