Ask Dr. SETI ®
When following the SETI station block diagram on the website, I notice that the microwave downconverter drives an SSB VHF receiver, typically at 144 MHz. Must the 144 MHz receiver be SSB? Why not AM? Or why can't I use my existing VHF FM scanner? After all, it tunes 144 MHz.
Eric (via email)
The Doctor Responds:
We do not contemplate that extraterrestrial civilizations will necessarily employ SSB modulation. Rather, an SSB receiver will convert whatever signal it happens to receive, with whatever modulation -- or even no modulation at all -- into audio tones. These tones can be digitized by a computer's sound card, and analyzed in software for the hallmarks of artificiality, those characteristics which confirm their extraterrestrial intelligent origin. The output from an FM or AM detector, on the other hand, may not contain audio components (especially in the case of an unmodulated carrier, which is a likely scheme for interstellar beacons), and thus would produce no useful output from a computer's sound card.
VHF receivers containing SSB detectors (sometimes called Multi-Mode or All-Mode receivers) are readily available through ham radio retailers, and commonly used by serious VHF/UHF amateurs. Check with your local ham radio club for specific recommendations.
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this page last updated 25 October 2003
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