Fall 2008 Issue
DR. SETI’s STARSHIP
By Dr. H. Paul Shuch, N6TX
Figure 1. Drift-scan sweep of Quasar 3C273,
about 3 dB out
How do you know if your rig is working? “Easy,” you say. “Just call CQ and see who answers.” True, but if the nearest DX is light years away, you can grow old, cold, and lonely awaiting that “QRZ” from Beyond. Such is the dilemma facing those radio amateurs pursuing interstellar DX, a practice otherwise known as SETI.
Maybe you’re not trying to work DX at all, but are just an SWL. This, in truth, is more the case for the hundreds of amateur observers in the grass-roots, nonprofit SETI League who build sensitive microwave receiving stations, seeking radio evidence of technological civilizations out there among the stars. A receiving station is less costly than one that also transmits, for two reasons. The obvious reason is that a shortwave listener need not invest in a transmitter. However, beyond that truism, on a galactic scale (where transmitters need to radiate power levels that boggle the imagination), being a passive listener puts the burden of generating gigawatts right where it belongs —squarely on the shoulders of our (presumably older, wiser, and wealthier) cosmic companions. Earth is, after all, a young planet orbiting a young star. Other species, if they exist, are likely to be more ancient. If their planet has an expanding economy (a principle terrestrial economists call “inflation”), then they can afford better than we to radiate incredibly strong beacons, which just might reach our modest receivers as incredibly weak noise.
Now, receiving those feeble signals on Earth
is no easy task. It requires searching through the quietest part of the
spectrum, with the highest gain antennas, the most efficient feeds, the
lowest noise receivers, and the cleverest digital signal processors we
can muster. Thus, radio astronomers (whether professional or amateur)
and those engaged in the scientific Search for Extra-Terrestrial
Intelligence go to great pains for that extra tenth of a dB of
sensitivity, as do weak-signal microwave DXers and moonbouncers. In
fact, the SETI and EME communities have such a commonality of purpose
that it makes good sense for them to share their technology, which is
where our story begins.
“You can’t work ’em if you can’t hear ’em,”
the saying goes. But how do you know if you can hear ’em, considering
you don’t even know for sure that they exist?
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