Joe Strout <joe@strout.net> wrote in message news:<joe-B9181C.14370606052004@comcast.ash.giganews.com>...

R> It has been claimed that a 1 watt transmitter would be sufficient
R> with modern receivers.

DW> I don't know where you got that figure.  You need very
DW> approximately 1GW EIRP from the nearest star to get the S@H
DW> threshold of 22 times mean noise power in 0.075Hz and time *
DW> bandwidth = 1.

Yes, I read this statement by Dave Woolley, and I see him asking the
same question.  Where did you get this 1 W figure?  It's wrong.  As
Dave states, a transmitter power closer to 1 GW (= 1,000,000,000 W) is
required.

Looks like the 1 watt argument was made by Lou Scheffer.

These two are exactly compatible.  If you broadcast omnidirectionally,
it takes about 1GW.  If you broadcast as directionally as you can, it
takes about 1W.  Antenna gain accounts for the whole difference.  For
example, the gain of Arecibo (at 3 cm) is about 10^9.

So both numbers are right, depending on whether you are using a
directional transmitter or not.  There is no hope (with anything
approaching current technology) of detecting a 1W omni-directional
transmitter at interstellar distances.

    Lou Scheffer