David:

I enjoyed your paper.

However I think there is one other category of ET transmission that is not
described in your paper: archeological transmission for the benefit of
future generations of the transmitter's society i.e. electronic time capsule

The purpose of these transmissions is not to contact intelligent
civilizations on other planets but to leave an electronic time capsule for
future generations of the transmitter's society on their own planet.

Reflected radar beams off distant exo-planets, gravitational lensing,
inter-stellar refraction and other techniques could be used so that a signal
sent from earth would some day return back to earth and be detected by
future generations.

The signal would be extremely weak - but knowing its characteristics should
make it easier detect for future technologically advanced societies.

If other ET civilizations have the same anthromorphic desire "to leave their
mark" then their would be a rationale for these societies to go to the
expense to carry out inter-stellar transmissions for many generations. It
is the same desire that we have had over many millennia to build pyramids,
castles and tombstones

Bill

Bill St.Arnaud <bill.st.arnaud@canarie.ca>