In article <48000adb.0402042157.2ef3955d@posting.google.com>,
exosearch@juno.com (Jason H.) wrote:

Perhaps some would think that the significance of that frequency has
everything to do with life, it being the bottom end of "The
Waterhole".  Indeed, back in 2000 David Woolley probably also wrote:

Only in combination with the 1.6GHz OH- line cluster.  In this thread,
it was fairly clear that the narrow definition was in use; that is
generally the case where people are complaining that "SETI" is not
searching enough of the spectrum (and it is confusion with the broad
definition that causes people to claim that it is low noise).  The narrow
definition is not based on biochemistry, although the analogy is of the
meeting place of the animals in the wild, which is vaguely biological.

In fact, I suspect that the the medium definition is much more a 
rationalisation of technology limitations than a real criterion.  I 
don't believe any current SETI project uses that definition to define
its search limits (SERENDIP might have approximated it if had 
covered the original planned 200MHz, but currently covers 100MHz
centred on 1.42GHz, but Phoenix goes well above the OH- lines).  The
optimum frequencies for communication are all above the OH- lines.
(If I remember correctly, "Contact" used pi * f(H[hypefine)), at
least in the book.)

The medium definition suffers from severe man made pollution from,
in particular, GPS satellite navigation signals.

(I did consider giving the three definitions in the current reply,
but I've already done that many times and I'm not sure that the term
"waterhole" was actually used.)