Re: Planetary rovers, SETI and other musings, was Re: update.356 (fwd)

[Steve Schear <schear@lvdi.net>]

>>> Speaking of which, do the current SETI programs check for signal
>>> modulation using polarization.
>
>Speaking of SETI, their current intent is to do a distributed
>computation spread across thousands of computers, similar to some of the
>keycracking efforts.  Details at http://www.bigscience.com ;
>the Recent News section says they're currently trying to figure
>out about funding.  Meanwhile, there's www.mersenne.org for
>factoring big prime numbers.

One of the problems I have with SETI is that it assumes that a distant
civilization is sending out a beacon for others to home in on, and that
this beacon is a narrowband signal. What if most such civilizations aren't
looking for anyone and merely going about their own affairs, including
communications for their own needs?

Because of path losses it takes an incredibly strong narrowband signal to
traverse even relatively small cosmological distances and have any hope of
detection with our technology.  For example, Earth's strongest TV signals
could be detected by our present technology out to about 50 light years,
but no image reconstruction would be possible (insufficient S/N).  The
highest power transmitter-directional antenna, at Aricebo, can be heard to
about 300 light years, but its only transmitted a SETI beacon once and only
for a few minutes.

An excellent way to mitigate path loss is trading bandwidth for data rate.
GPS  garners an incredible 63 dB of process gain (or about a 2,000,0000
fold improvement) in this manner. If I was trying to send a electromagnetic
signal vast distances I'd use some form of spread spectrum.  Individually,
narrowband receivers are most insensitive to broadband 'noise' sources.
However, I wonder if it might be possible to configure the SETI@home
software to coordinate the narrowband channels signal analysis so as to
have a better chance of detecting broadband, pseudo-noise, signaling.

--Steve