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A Quad-Helix Antenna For Hydrogen Line SETI
by William H. Black, K4BSN (

While reading the Winter 1999 issue of SearchLites, I noted with interest the letter from SB, Winston-Salem, NC, asking about using the small 16" dishes for SETI. The writer did not mention what frequencies he wanted to use, but he obviously has a space/restriction problem, as do many others who are interested in the SETI search program.

Recent progress in building my ARGUS station has produced an antenna which provides a realistic and formidable possibility for those observers who want to develop a SETI monitoring station, but are hampered by space, covenants, restrictions, etc. I started building my station early this year, but I have since moved to a house where I have two acres of land with no restrictions, and I recently acquired a brand new Paraclipse Classic 12 dish from a dealer who apparently waited too late to unload it at its retail price.

click on thumbnail to view full-sized image The helix quad antenna is shown in the accompanying pictures. I purchased the individual helix elements from Olde Antenna Lab, and built them into the quad structure as shown. The antenna is available as a pre-built quad, eliminating the need for the power divider. I got the single helix elements because of an interest in experimenting with an interferometer.

click on thumbnail to view full-sized image The size of the helix quad is 21" X 21" X 27", about one fourth of a cubic yard. According to specs provided, each helix has a nominal gain of 18 db, so the quad has a gain of around 24 db at 1420 MHz. That is a very usable antenna, and occupies about the volume of a medium-sized TV set. The helix elements can be purchased with fewer turns for an even smaller structure, but with less gain.

click on thumbnail to view full-sized image I know there is nothing here that isn't old hat to many of our members, but I also feel very strongly that anybody, (who has the basic technical requisites), despite space/covenant limitations, can get a station up and running with this type of antenna. It is a great way to get started, and can be developed into a larger antenna system when/if more space becomes available.

I hope that this information is helpful. I would be happy to assist any member who wants to buy/build similar antennas to join the search.

William H. Black, K4BSN

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