From: Steve Schear <schear@lvcm.com>
Date: Sun, 8 Nov 1998 12:57:00 +0800
To: "Vladimir Z. Nuri" <vznuri@netcom.com>
Subject: Re: IP: Discover Alien Life With Your PC And SETI
In-Reply-To: <199811072128.NAA19768@netcom13.netcom.com>
Message-ID: <v04003a03b26ac9032df6@[24.1.50.17]>
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Perhaps I'm missing something, but it seems to me that if I were an alien
civilization and wanted to send out a beacon, in as wide an angle as
possible, across the vast reaches of space and overcome as much of the path
losses as possible using the least energy I certainly wouldn't use a narrow
band signal. Quite the contrary, I'd want to spread a low bandwidth
information signal across the widest practical spectrum. Its much easier to
increase process gain (the ratio of the baseband information signal to the
final carrier bandwidth) than transmit power.

While a narrow band signal from Arecibo's powerful transmitter/antenna
combination can be detected at a distance of about 300 light years. It
subtends a very small angle greatly reducing the likelyhood of contact.
Switching to a spread spectrum approach could allow broadening the antenna
pattern, and thereby its chances of detection, significantly without
reducing its effective range. Notice how 63 dB (or over 2,000,000 fold
effective increase in transmit power) of process gain enables handheld GPS
receivers to pull in signals from satellites, sent using only a few watts
of transmit power, without much of an antenna.

If all this seems to make sense, then why are the SETI people apparently
seaching the skies with lots of narrow band receivers? They don't seem to
be employing any broadband correlator techniques, so spread signals will
probably be missed.

--Steve