In semi-infinite wisdom Louis Scheffer answered:

Rich <someone@somewhere.com> writes:

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.

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?

For stars near the ecliptic (ours or theirs), you will get occasional eclipses, but a very small fraction of the time.

So you don't think that the rotating planet will get in the
way, or that when the transmitter is pointing at or near the
sun, it will interfere?

For most stars, 100% coverage is posible.

I would think that for half the day, coverage of any point
would be impossible for any planet bound transmitter.

A northern hemisphere
transmitter can send to stars near Polaris, for example,
full time with no eclipses or outages.  A southern
hemisphere transmitter can so the same for the stars
near their pole.

And atmospheric effects would be maximum.

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?

Good idea, but it's already developed.  The IEEE database has more than 500 papers on phased-array radars alone.

The military's been using them for years, but I was responding
to this text...

# just like your hologram proposal below.

Which you cut for some reason.

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.

    http://www.pavepaws.org/About.htm

    [...]

    The RF signals transmitted from each of the array
    faces form one narrow main beam with a width of 2.2
    degrees. Most of the energy is contained in the main
    beam. Each of the main beams can be directed
    electronically between 3 and 85 degrees above horizontal.

While 2.2 degrees may be great for early warning radars,
it seems a bit broad for transmitting to other stars.

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?

Yes.  I'm on the Science and Technology Working Group of the
SETI Institute.  I'm a co-author and editor of the book SETI 2020,
and wrote the appendix on microwave transmitters for SETI.
I'm on the technical advisory board of the Allen Telescope
Array.  I wrote the band-splitting code used in the SETI@home
servers.  So I've contacted most of the serious SETI folks.

So it would seem.

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'm reminded
of a thread where one of the administrators of the WISE program
in the UK was posting. Seems he was certain that favoring the
girls would create better engineers, although he never explained
why. But he had a vested interest in the program, and objectivity
was not his forte, nor was there any sexism that favored girls
so blatant that he could so much as identify it.

There are some issues with ugly beam patterns, ground plane problems,
etc with active arrays that I will research time allowing. But
assuming you have everything correct (and that it's built correctly),
what do you think the chances of success are?

Rich

    Lou Scheffer