In article <pboZZDA9oMYBFw79@econym.demon.co.uk>,
Mike Williams <nospam@econym.demon.co.uk> wrote:

Several SETI projects scan the entire band where the background noise is

I'm not aware of that.  I thought the upper frequency limit of all
of all the radio ones were limited by engineering and financial
considerations.

reasonably low. Below about 1 GHz there's too much noise from natural
terrestrial sources for the search to be feasible and above 10 GHz
there's too much noise from the galaxy.

You have these the wrong way round.  Galactic (synchrotron) noise 
dominates below about 1Ghz and atmospheric (water vapour) noise
dominates above about 20GHz (quantum noise also starts to build
up at higher frequencies).  You have to come down to about 50MHz
before ionospheric effects start to bite, at which point galactic
noise is really quite high.

It would be nice to run a SETI project from above the atmosphere, where
lower frequencies could be scanned, but the cost of one satellite would

Consequently, you mean higher, here.  The real advantage only comes when
you put the moon behind you, as the real problem is man made noise which
makes much of the wide definition (low noise) water hole unusable.