"Rob Dekker" <rob@verific.com> writes:

"Louis Scheffer" <lou@cadence.com> wrote in message
news:4095e404$1@news.cadence.com...

Andrew Nowicki <andrew@nospam.com> writes:

[...]  As a first guess, cover the planetary zones
of the nearest million stars or so, with beams that are on
all the time  [Think of the beams as looking like a pincushion].

This is something we can do with existing technology for about
$200M, for a beam bright enough that we ourselves can detect it.
And this cost will come down further as a consequence of Moore's
law.

    Lou Scheffer

How did you get to just $200M for a system which cover 1M stars;
semi-continuously ?

Here's how I got that number.  Assume you build a large phased array consisting of
many small (10mw) transmitters.  To be detectable by ourselves, you need about a
10^12 watt EIRP.  1M of these implies a total EIRP of 10^18 watts (it turns out with
phased arrays the total EIRP can be split up with almost no penalty).  This means
you need 10^10, or 10B transmitters.  We can build today a 10mw transmitter plus
antenna for about $0.20 (actually we can build a chip with 100 of these + a PC board
with 100 antennas for about $20, but for our purposes this is the same.)

This gives a total cost of $2B for the transmitters.  However, you are ordering
100 million identical PC boards and chips, so you should get a substantial volume
discount.  How much?  I'm guessing a factor of 10 since it would be reasonable to
set up a dedicated production line for these volumes.

How much power do you need for the transmitters ? 

About 200MW is required for 10^10 10mw transmitters at 50% efficiency.

Which cost/W do you use ?

At $0.08/kwh this is about $140M/year.  However, you could also make the array
solar powered to cut the operating expense (though this reduces your coverage
since you cannot transmit at night, and introduces more site selection limitations).
You need about 32 watts/m^2 of low voltage DC - a great match to solar cell technology.

And how large is the antenna that you need ?

At about 3.5cm wavelength, the antennas need to be about 2.5 cm apart, or 1600 per
square meter.  This yields a surface about 2.5 km on a side - big, but not that
much bigger than the proposed square kilometer array.  And it's a lot lower
technology.

No matter how I try, I cannot get this cost number to below billions of
dollars. Per year!
Either way, doesn't your cost go down if you increase your frequency,
and start pulsing rather than transmitting contiuously ?

Yes, increasing the frequency can be good, especially if your costs are
dominated by the area of the transmitter.  However, this is not always the
case.

What if you go to infrared or higher transmitters ? Wouldn't cost go down
many orders of magnitude (Because you can make ns pulses )

The costs look similar since antennas (telescopes) are much more expensive 
per unit area, since they must be much more precise, and the photons 
are much more costly compared to the backgound noise.  Overall, it's hard 
to tell if short pulses in the IR/visible are better than microwaves.  That's
why the SETI 2020 report recommended looking for both.

and 'antenna' size reduces to a small telescope...

Yes, but one of the two ends (the receiver or the transmitter) needs one 
(meter class) telescope per star.  If both the transmitter and receiver
just look at one star at a time, the odds are the reciever won't be looking
when the sender is sending. One of the two has to be looking (or sending)
all the time at all the targets to have any appreciable chance of success.
And 1M telescopes are currently much, much more than $10K each, so you are
talking one end or the other spending at least $10B dollars.

It is more likely to find a beacon signal at the frequency, bandwidth, pulse
rate and pulse width which is most cost-effective for ET to produce and
detectable for us...

This is a very good question, but turns out to quite sensitive to assumptions
about ET technology.  So it's hard to find a good answer.

Did anyone make a formula for this already ?

The most serious attempt is in 'SETI 2020', chapter 5.  

    Lou Scheffer