SETI League Technical Manual -- SystemsI joined The SETI League a few months ago. Please tell me how I may come by the simplest information that will tell me in recipe-like form how to set up my own search effort. I need this to be ultimately simplistic.....You connect a to b to c and flip the switch, etc...I very much like the idea of SETI but I have minimal background in such things.
Dr. SETI replies:
I wish it were that simple, but then, if it were, someone would have done this years ago. Your inquiry is typical of a number we have received since we kicked off our Project Argus search and, although we welcome such queries, the answers may well disappoint some of our members. I am reminded of the early days of satellite TV. Many people asked then exactly what equipment to buy, where to obtain it, and how to hook it up. Although my colleagues and I conducted classes and wrote articles aplenty, there were no easy answers then, any more than there are for SETI now.
The first commercial home satellite TV system, which I helped to produce in about 1978, was something of a hodge-podge. I developed the microwave circuitry, and married it to a video demodulator circuit designed by Stanford University's Prof. Tay Howard. For an antenna, we used a 4.7-meter dish designed by John Kinik of Kintech Technology, a feedhorn from Bob Taggart of Chapparel Communications, and a 180 Kelvin low-noise amplifier designed by Art Kawai of Dexcel. We put the first prototype together in my backyard on about a $4000 budget, and managed to receive marginally noisy video. That early system was probably duplicated a couple of thousand times, but no two systems were configured exactly alike. Early TVRO experimenters used their considerable expertise to improve on existing technology, and in due course a whole industry was born. Today, you can walk in to any Sears, Radio Shack or K-Mart store and buy a complete package for about $500. But it took two decades of commercial development following the pioneering efforts to reach that point.
The state of amateur SETI today pretty well coincides with those exciting early days of the satellite TV business. Only it's not an industry, but a scientific cause which we are attempting to champion. Now, as then, there is no cookbook, no set of recipes, no blueprint, no road map to guide the pioneer. No two of the first half-dozen Argus stations are very much alike. And The SETI League assiduously avoids telling its members exactly what equipment to buy, and how to hook it up, lest we stifle their creativity.
On the other hand, not every one of our members has the engineering expertise necessary to design a SETI station from the ground up. Nor is that a prerequisite to good science. Many people with more enthusiasm than formal training are in a position to make major technical contributions. I still maintain that when The Signal is detected and verified, it will have been an amateur, not a professional radio astronomer, whom we will have to thank. And many of these amateurs, like the member who asked the question which opened this discussion, are seeking assistance and guidance. The SETI League fully intends to provide the required help. Only as these systems are still evolving, the answers will be tentative and the designs cast in jello.
Let's start by defining the minimum equipment necessary to do a credible job at microwave SETI, as depicted in Dan Fox's very fine System Block Diagram. You will need, of course, an antenna and feedhorn, a low-noise preamplifier, a microwave receiver, and a suitable computer running some kind of digital signal processing software. A number of useful accessories will round out the SETI station. There are sections in this Technical Manual corresponding to each of these areas, but the choices are so diverse as to boggle the mind. Is there anything we can do to narrow things down a bit?
In fact, there is. I can tell you exactly what hardware and software I used in the first Argus station at SETI League headquarters. I didn't go with the least expensive choices in each category, or necessarily the best. I opted for expediency in order to get a station on the air in time for our April 21, 1996 launch ceremonies and, yes, I cut a few corners in the process. You probably won't want to duplicate my station exactly as I implemented it, but at least this will give you a starting point. As more stations come on the air, better solutions to the problems of amateur SETI will make themselves known. Some of these will come from you, and I hope you'll share them with your fellow League members.
The headquarters station is depicted in the accompanying photographs. Though just about any surplus satellite TV dish in the 3- to 5-meter diameter range would suffice, the antenna we chose for our first system is a Paraclipse Classic 12, with horizon-to-horizon mount. This 3.7 meter diameter dish has a focal length to diameter ratio which makes it easy to illuminate with a simple cylindrical waveguide feedhorn (in our case the Lichtman feed), at about 50 percent efficiency. As the antenna is slightly under-illuminated, sidelobes and antenna noise temperature are reduced. We have recently added a choke ring to this feedhorn, to significantly reduce noise sidelobes and improve overall system performance. The robust Paraclipse mount and chain-drive rotor were modified for meridian transit mount with full 180 degree elevation rotation.
Our own SETI League GaAs MMIC (Gallium Arsenide Monolithic Microwave Integrated Circuit) low-noise amplifier, as manufactured by Down East Microwave, is mounted directly on the feed with a male-to-male type N coaxial adapter. The next generation preamp, now in the design phase, will employ a GaAs PHEMT (Pseudomorphic High Electron Mobility Transistor) device in front of the existing MMIC stage, for a significant reduction in front-end noise. At present, no bandpass filter is being used behind the preamp, although in RF polluted areas it might be wise to add one. Though not a commercial product, the microstrip filter depicted in the Technical Manual is probably a good bet. We expect to add such a filter to our station at a later date.
Twenty-five feet of RG-8 coaxial cable, with type N connectors installed, connect the LNA to an Icom 7000 microwave receiver. We have recently replaceed this receiver with a homebrew downconverter driving a VHF receiver, although the Icom is certainly a good bet for those who prefer to purchase a commercial receiver. Receiver audio output is applied to the microphone input of a Texas Instruments model 560CDT multimedia laptop computer, which uses a 75 MHz Pentium CPU. In fact, much less costly computers of the 486DX variety would be perfectly acceptable, at a fraction of the price. The DSP software we are currently using is Spectra Plus, although, again, any of the low-cost shareware programs discussed in the Technical Manual are certainly acceptable. We have yet to obtain suitable SETI logging software, so at present one must stare at a computer screen and evaluate the incoming signals. This is a weakness in the first Argus systems which we hope our members will help us to overcome.
It must be emphasized that this station is not the only, indeed not necessarily the best, approach to amateur SETI. It does, however, achieve the design objectives of full Water-Hole coverage at sensitivities adequate for the detection of Wow! type signals. If all components are purchased new, it can be duplicated in its entirety at a cost of about $7,000 US. (Half of that cost is tied up in the particular multimedia laptop computer we chose.) This is certainly quite a bit more than one need spend for an effective SETI station. In fact, using a more modest computer and dish, the price quickly drops in half, for no discernible difference in performance. And if one uses an existing computer, a surplus dish, and builds some of the RF hardware from kits rather than purchasing it assembled, then the basic design is duplicable for well under $1000 US. Thus, the system just described should be considered as a proof-of-concept effort, nothing more.
All that said, you may still feel yourself in need of some hand-holding, and that's OK. Unfortunately, there are hundreds (soon thousands) of you and only one of me. But the level of technical expertise found within The SETI League is truly impressive, as is the spirit of cooperation prevalent. There are a number of ways in which you can collaborate with your fellow SETI enthusiasts, to mutual benefit. For starters, a SETI League Membership Directory (first published in July of 1996) is being distributed to all members, and will be updated annually. It is sorted by country and state, so you can easily locate other members in your region. In England and Germany (and soon, we hope, in other areas), volunteer Area Coordinators have accepted the task of assisting their countrymen in getting up and running. These individuals will be indicated in future Directories.
Try to locate a local amateur radio club, or regional microwave society. Many of these organizations have Web sites which you can access through our Other Web Resources pages. Check out some of the meetings listed in our Conference Calendar. Check the various amateur radio magazines available in your country and language, for other meetings of which we may be unaware. Don't overlook astronomy societies, or any local college or university which might have applicable classes or clubs. There's a wealth of information and assistance available, but you have to be willing to seek it out.
And above all else, when the day comes (as indeed it will) that you have become a senior SETIzen, please be willing to share your expertise with others, as others will have shared theirs with you. This may well prove a multi-generational enterprise. If we don't start training the next generation now, we (as an organization, and a civilization) may not be around when The Call comes in.
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