In semi-infinite wisdom Louis Scheffer answered:

Andrew Nowicki <andrew@nospam.com> writes:

[...]

If your message lasts 10
seconds and you are sending it to one million stars,
the same star receives the message about once every
3 months. If their SETI program works like our program,
they will probably miss our message.

Perhaps I was not clear.  All the beams, shining on all the stars,
are on all the time,

Just where do you plan to place your transmitter so that it
will not be obstructed by a planet or it's star periodically?

just like your hologram proposal below. 

I'm not quite sure I understand that proposal.

Whenever the receiver looks, they will see it.  This
is precisely to avoid the problem you just stated.

Gee, that technology would come in handy on Earth. Maybe
you should develop it?

I have a better idea: a parallel, modulated microwave
beam is made by a conventional transmitter. A microwave
hologram splits the beam into thousands of narrow beams
aimed at the stars.

This is *exactly* what a phased array transmitter does,
except it generates the radiation locally at each point,
rather than by scattering coherent radiation from a central
source.

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

The math is identical.  However, the phased array
is able to cope with changes much better (as the stars move
with respect to each other, or you add more stars, you would need to change the hologram.)  With a phased array
you just update the coefficients with no physical changes.

Have you contacted the SETI people?

Rich

    Lou Scheffer