Rob,

"Rob Dekker" wrote in message
m...

"Alfred A. Aburto Jr." wrote in message
. com...
....
The most powerful sources are radars. They operate all over the 1-100
GHz
band. Long range radars operate in the so-called "L-Band" which runs
from 1
to 2 GHz. There are also "S-Band" radars in the 2-4 GHz ("C-Band is
4-8GHz,
..., "O Band" is 60-90GHz) ... notice that the L-Band radar covers the
water-hole region near 1.420406 GHz.

Radars are used for many purposes and they are found around the world
operating day and night ...

I'm almost ("almost" because I'm lacking specific and sufficient data)
certain that, say, the Parkes (210 ft? diameter) radio telescope could
detect emissions from an equivalent Earth place at the distance of Alpha
Centauri.

Well, Here goes. Use seti FAQ formula :

If we have a 300ft diameter dish (radius==50m), receiving a signal
from 5 LYs (Alpha Centauri) away, and lets assume we need 10dB S/N ratio
to make it recognizable, with receiver system temp of about 100K (pretty
good receiver in microwave), then the transmitter needs to radiate with
40GW EIRP.

That is assuming it is a CW pulse (not modulated, only one pulse), and
that we are
using all information in the signal, so that a 1ms pulse of this power (by
definition at
least 1kHz wide) will not go unnoticed.
I'm not sure if such pulses would go by unnoticed by seti@home. Do you
know ?

40GW EIRP.

I don't know enough about radar to tell you if that is frequently used
here on
earth, and for which purpose, but to radiate that around 1.4GHz you need a
lot of line-power, (10's or 100's of KW's) and a pretty decent size dish
(10's of meters).
A airtraffic control radar signal will not make it I think.

So only radar for very special applications (military high-sensitivity
radar) or
astroid radar would create that amount of power. And these are not
transmitting
too frequently. And thus the signal would not be 'reproducable', and thus
we can't prove or dis-prove if the signal is actually artificial and from
Alpha Centauri.

So I think we can't detect a earth-like civilisation even it there is one
around Alpha Centauri.

..
snipsnap

Ah! So you read the FAQ. Humm :-) That's great!

I'll check into this too ...
(I wish I knew more about military radars myself ... space surviellance
radars for example)

You're right though, sounds like a special radar is needed.

Arecibo, of course, is a very special radar and very powerful one too used
in part for pinging off Solar System objects (planets, asteroids...)
(100 KW omni power isn't much though generally speaking nowadays)

(Arecibo, I think, transmits at 1-10 Megawatts ...it "can" put 10's of
terrawatts of power in a narrowband beam)
I wouln't count Arecibo though, because the odds of detection, even with
great SNR, would be very slim (one might need to look our way for ages
before one saw a ping ...)

I distinctly remember that some of the military radars could be detected 100
LY's away ... but I'll recheck all this ...

I'll get back here soon ...
Al