Rich <someone@somewhere.com> writes:

As I understand it, a phased array can only transmit or
receive in one direction at a time.

This is incorrect.  A phased array can transmit (or receive)
in as many directions as it has elements, within the field
of view of a primary element (which can be very large for
transmitters).

Hmm, guess I was thinking of passive arrays.

A little research shows some constraints, one of which is
beam width. Were you planning on transmitting, you would
not get anywhere near the 10 AU beam spread being discussed
in another thread for any nearby star.

Yes, you want the narrowest beams possible.  An array we could
afford today might be 300 meters across, running at 3cm
wavelengths, so the beam is about 1/10000 of a radian wide, or
about 0.0057 degrees.  At 10 light years, this would
spread to about 10^13 meters across, or 70 AU.  Not as good
as you would like, but about 100,000,000 times better than
omni-directional.

While 2.2 degrees [the Pave Paws beam width] may be great 

for early warning radars, >it seems a bit broad for 
transmitting to other stars.

Absolutely, see above.  Remember the military does not need
or want the narrowest beams possible.  They want better coverage
at shorter distances.

Don't take this as an attack, it's not meant as one, but it seems
that you have a vested interest in this project. 

I have my personal biases, like everyone else.

But assuming you have everything correct (and that it's built correctly),
what do you think the chances of success are?

I'm absolutely certain we could build a powerful microwave beacon
and train it on the stars.  We can demonstrate that it's working by
bouncing radar echos off the outer planets.

Should we start deliberately transmitting to the stars?  I'm not
sure (there are lots of ethics issues) but I'm leaning towards yes,
on the grounds that we are transmitting already whether we like
it or not.  Plus that way we are at least consistent when listening
for deliberate transmissions.

Will SETI succeed?  This is a very open question - we just don't
know enough to judge our chances.  There seems to be lots of planets -
do many (or any) of them develop life?  Does the life become
intelligent?  Is it technological and wants to communicate?
All of these are hard questions, and the eventual answer seems
impossible to predict at this point.

Are SETI searches worth the small amount we spend on them?
Absolutely, this is one of those high risk, high payoff gambles.

   Lou Scheffer