Andrew Nowicki wrote:

Worse yet, they seem to believe that some extraterrestrial
civilizations have been sending powerful microwave beams
toward the Earth for millions of years. Why would the
extraterrestrial tax payers support such an effort?

Lou Scheffer wrote:

This is a reasonable question.  Why look for a signal that no one is
motivated to send?  However, it turns out this signal is not very
expensive to transmit. (see the appendix on beacon construction in the
book SETI 2020.)  If you target your beam so it only covers the
targeted solar system, it takes less than 1 watt per system covered.
So for 1 MW of power, costing at current rates about $700,000 per
year, you could hit each of the nearest 1 million stars with a beam
strong enough that we ourselves could detect it.  Although building
the transmitter costs somewhat more, it's still on the order of
existing SETI expenditures.

If we treat the Sun as a black body, intensity of its
microwave radiation at 100 GHz is about 10 million times
smaller than intensity of its visible radiation. The total
visible output of the Sun is on the order of 10^17W, so the
total microwave output of the Sun is on the order of 10^10W.

If the ET lives near a sun-like star and beams to us 1 watt
of microwave signals, his star makes so much microwave noise
that we cannot read the signal unless one beep lasts at least
10^10 seconds (about 300 years).

The signal-to-noise ratio improves 3 orders of magnitude
when the ET's microwave transmitter is moved away from
their star. If the ET replaces his microwave transmitter
with a laser and moves it away from his star, the
signal-to-noise ratio improves at least 20 orders of
magnitude, if we ignore the noise made by our Sun and
terrestrial atmosphere. Moving the laser away from the
star creates a problem: we have to guess where it is.
The natural place for the laser is dark side of a
large, conspicuous planet.