Hi everyone,

So far SETI radio investigations seem to be concentrated on finding
narrowband beacon signals from alien civilisations.

Now, I believe the probability of any alien civilisation announcing
their existence into the far and unknown, with a consistent program,
is extremely low, and the likelyhood of narrowband transmissions
for beacons is almost noneexistent in my opinion. For beacons,
pulsed light is much more cost effective.

In this posting, I'd just like to see if anyone is aware of any project
done, or ongoing or planned which looks for a much more likely
source of proof of ETI presence : radio leakage.

I found three sources of high-power radio transmissions which we
as TI radiate into space :

  - Planetary TV : 100Mhz-1Ghz. Continuous. Power 10-100kW. Not well
directed.
  - Planetary Radar. 1Mhz-100Ghz. Power 1kW-1000kW pulses. Directed but
infrequent.
  - Satelite uplink. 1Ghz-20Ghz. Directed. Power 10W-10kW. Continuous. BW
10-100Mhz.

More developed civilisations might have higher-power, continous
transmissions to colonized planets, but such transmissions will be
very narrowly directed, and thus have low probablility of detection,
even though their power would be immense.
Maybe the "WOW" signal was one of them....
For now, I stick with the presently known forms of high-power
transmissions.

Planetary TV transmissions are too poorly directed to be
detected far away, and planetary radar is irratic and infrequent,
and is likely to require less power with technological development.

But Satelite uplinks are very interesting : Satelites are a relatively
low-cost solution for remote-area broadcasts, and thus are likely to remain
for a long time, even if technology develops further.
And they are continous, well-directed, pretty high power, there are
many of them (eath's sat-uplinks count in the thousands) and in
the sweet 1-20Ghz range to minimize atmospheric interference.
Great signals, which broadcast deep into space !

The only difference between sat-uplinks and our ET search is that
they are broad-band (we humans use 10-100Mhz transponder signals),
and ET signal search is narrowband, to reduce noise influence.

How would we detect such sat-uplink signals ?
Apart from their power being distributed in broadband (10-100Mhz is
a reasonable guess), they will come to us in bursts of 10-100sec.
This is because the uplink antenna is fixed on the satelite, and
thus they are beamed at us for they aparture/planet-rotation time.
Also, they will be very weak. Below noise level.

But noise consistent over time : if we were to listen to a broad band
spectrum
for a considerable time (say 100 sec) and accumulate all noise
photons over that time before we run the signal through a spectrum
analyzer, we will reduce noise influence by a factor of 100 over
a 1Hz bandwidth signal.

Effectively, we obtain sensitivity of 1/100 Hz bandwidth if we
listen to any signal (of any bandwidth) for 100 sec.
That's phenominal sensitivity !

In fact, my initial calculations show that we should be
able to detect a 10kW sat-uplink signal transmitted with a 10m dish
at 10Ghz up to 100 lightyears from earth with a our present technology....
We can do some calculations later.

For now, I wonder if any program has focused on this (weak broadband
signals)
already, or if this idea (of detecting broadband signals) has already
been proven to fail...

Your comments and feedback please...

Rob Dekker
Oakland, CA