In article <40291e8f$0$6843$cc9e4d1f@news.dial.pipex.com>,
Barry Walsh <bwalsh@SPAMMERSAREVERMINindigo.ie> wrote:

                     SETI is entirely passive and only receives signals 
at Arecibo.

This sentence is incorrect and parses ambiguously.  SETI is mainly passive
but there have been token active SETI transmissions, a long time ago from
Arecibo (as as PR stunt) and recently from the Ukraine (as clients for a
North American business), as well as some with totally inadequate power).
One parse of the sentence, i.e. that Arecibo is the only antenna used for
SETI reception is definitely untrue.  The other parse, that Arecibo's
SETI work is purely passive, has been true for over a decade, but is
not absolutely true.  Arecibo is far from passive for near earth objects.

Incidentally, radar is used for asteroid and comment tracking, although
the initial observation is normally optical.  This is one of the primary
activities of Arecibo, and it has a 1MW feed point, 10s of Terrawatt
EIRP, transmitter for this purpose.  Although not within the definition
of SETI (it is called SETV or SETA) I would think that optical detection
would be the most reliable method of detecting non-human engineered
spacecraft in the earth's vicinity.

Planetary radar transmissions are around 2.4GHz and wouldn't result in 
echoes in the frequency range used by S@H.  They would result in echoes
in the frequency range used by project Phoenix, but they wouldn't book
time that conflicted with radar transmissions, and don't provide
data for public processing.

Optical methods were used and probably still are used, for cataloguing
debris and potential weapons, in low earth orbit.

Otherwise, I would agree that the question reflected a rather poor
understanding of what the client does.