A of E author in alien light signal detection project

[Don Klipstein]

I seriously doubt if anyone who has the power to communicate between star
systems would use electromagnetic radiation to do it. What's the status
on gravity waves these days? How about quantum black holes? ;-)

Well, I could comment a bit on gravity waves vs. lasers.

Consider wavelength, and how that limits narrowness of a beam.

If I wanted to be noticed by someone on a planet 30 lightyears away, I
would get the biggest Nd:YAG ("YAG") laser that I could get and fire it
through a large telescope.

Let's see what happens if I get a 25 megawatt peak pulse YAG laser (1064
nm) and fire it out a telescope whose objective is 3 meters in diameter.
I try Google and find 25 MW YAG lasers have been made, and Earth's
biggest telescope is about 5 meters last time I checked (long ago).

If I don't have things terribly wrong, good optics can get the beamwidth
in radians down to not much more than the ratio of wavelength to objective
diameter. With a micrometer and 3 meters, that's 1/3 microradian or a bit
more, with cross section of the beam being about 1E-13 steradian.
25 megawatts into this is 2.5E20 watts per steradian.

Maybe that will be weak compared to output from the sun... Let's see...

I am figuring the sun to give us 1380 watts per square meter from
1.497E11 meters away. That's about 3.1E25 watts per steradian...

This does mean that a pulse train fired from a 25 MW peak power YAG
laser through a 3 meter telescope will be about 51 dB below the sun's
output.

Now, suppose aliens are checking us out with a narrowband filter or
having a computer monitor a spectral power distribution of our solar
system for patterned spikes? If we are not doing the same, then I think
we should!
I certainly know that a spectrometer costing only a few thousand $ has
resolution down to a few nanometers. It appears to me that not too many
megabucks are needed to have a computer-monitored spectrometer with
resolution of 1/10 nanometer and checking by the microsecond, and with
alerts beeped out and spectral power distribution curves logged if a
discernably non-random pattern of a spectral spike is detected.
If we are not doing this, I don't think it's much of a waste of taxpayer
money to get a few of these up and running to monitor at least parttime
the main sequence stars within maybe 30-50 light-years and of spectral
class lower or middle F to upper K or so.
And I also think it's worthwhile to have a setup or a few firing pulse
trains of laser radiation towards such stars.

But back to calculating numbers:

Portion of solar output in a 1 nm wide band at 1064 nm: .048% of 3.1E25
w/sr, which is about 1.5E22 w/sr. I am proposing 2.5E20 w/sr competing
against that, which is about 17 dB down.

Now, I will assume that better-achievable high power lasers will have
wavelength known to the .1 nm range and that monitoring of a spectral
power distribution of "optical band" output of a star system can watch
for this. Now we only have to watch for non-random patterns at selected
wavelengths to be monitored having patterns 7 dB below the output in same
bandwidth from a sun-like star, assuming their capabilities for producing
patterned laser bursts are what I mentioned above.

Now for an alternative spectral region to monitor: Radio bands.
Possibly it might be worthwhile to see if nuclear explosives get detonated
in the outer atmospheres of other planets - for whatever purpose!

- Don Klipstein ([email protected])

 

[Lostgallifreyan]

[email protected] (Don Klipstein) wrote in

Well, I could comment a bit on gravity waves vs. lasers.

Consider wavelength, and how that limits narrowness of a beam.

If I wanted to be noticed by someone on a planet 30 lightyears away,
I
would get the biggest Nd:YAG ("YAG") laser that I could get and fire
it through a large telescope.

Let's see what happens if I get a 25 megawatt peak pulse YAG laser
(1064
nm) and fire it out a telescope whose objective is 3 meters in
diameter.
I try Google and find 25 MW YAG lasers have been made, and Earth's
biggest telescope is about 5 meters last time I checked (long ago).

If I don't have things terribly wrong, good optics can get the
beamwidth
in radians down to not much more than the ratio of wavelength to
objective diameter. With a micrometer and 3 meters, that's 1/3
microradian or a bit more, with cross section of the beam being about
1E-13 steradian.
25 megawatts into this is 2.5E20 watts per steradian.

Maybe that will be weak compared to output from the sun... Let's
see...

I am figuring the sun to give us 1380 watts per square meter from
1.497E11 meters away. That's about 3.1E25 watts per steradian...

This does mean that a pulse train fired from a 25 MW peak power YAG
laser through a 3 meter telescope will be about 51 dB below the sun's
output.

Now, suppose aliens are checking us out with a narrowband filter or
having a computer monitor a spectral power distribution of our solar
system for patterned spikes? If we are not doing the same, then I
think we should!
I certainly know that a spectrometer costing only a few thousand $
has
resolution down to a few nanometers. It appears to me that not too
many megabucks are needed to have a computer-monitored spectrometer
with resolution of 1/10 nanometer and checking by the microsecond, and
with alerts beeped out and spectral power distribution curves logged
if a discernably non-random pattern of a spectral spike is detected.
If we are not doing this, I don't think it's much of a waste of
taxpayer
money to get a few of these up and running to monitor at least
parttime the main sequence stars within maybe 30-50 light-years and of
spectral class lower or middle F to upper K or so.
And I also think it's worthwhile to have a setup or a few firing
pulse
trains of laser radiation towards such stars.

But back to calculating numbers:

Portion of solar output in a 1 nm wide band at 1064 nm: .048% of
3.1E25 w/sr, which is about 1.5E22 w/sr. I am proposing 2.5E20 w/sr
competing against that, which is about 17 dB down.

Now, I will assume that better-achievable high power lasers will
have
wavelength known to the .1 nm range and that monitoring of a spectral
power distribution of "optical band" output of a star system can watch
for this. Now we only have to watch for non-random patterns at
selected wavelengths to be monitored having patterns 7 dB below the
output in same bandwidth from a sun-like star, assuming their
capabilities for producing patterned laser bursts are what I mentioned
above.

Now for an alternative spectral region to monitor: Radio bands.
Possibly it might be worthwhile to see if nuclear explosives get
detonated in the outer atmospheres of other planets - for whatever
purpose!

- Don Klipstein ([email protected])

Thankyou. I can see what I was missing now. The beam of a CW laser diverges
more, fades over distance more than the sun's light does, and I wasn't
taking that into account properly.

I don't know much about extracting signals from noise, but I tried it with
sounds. 1KHz pulsed at 1Hz with 50% on-time, against a background of white
noise. I could hear it down to -30 dB, but only down to -24dB reliably,
which is lower than your -17 dB, so that should work. Shorter pulses would
make it harder though. One thing I noticed was that it didn't matter if I
filtered the mix or not, it had no effect on my ability to pick out the
sine wave, it only made the test a little more comfortable to listen to.
If anything though, the wideband background provided a better anchor for my
perception of the narrowband one than the filtered mix did. Whether that
effect would be the same for a mechanical monitor I don't know. It might
have been due to a poor quality filter too.

What this leads me to ask is: could it be better to convert light signals
to sounds or other representations to let human perception do the
filtering, to take advantage of perception we haven't learned to model?
Could that work better than doing it entirely by mechanism? I know that
this must happen anyway with all measurements, but my point is that science
tends to refine as much as possible before human interpretation is allowed,
and this might not be the best way. A human can pick out the tune and the
harmony in music, even in an instrument low in the sound mix. This is
enhanced dramatically in a a two-channel stereo mix. No-one's modelled that
and made a machine do it, the results so far have been a joke, so if human
perception is allowed to have a greater share of detection, we might get
better results.

 

[Winfield Hill]

Don Klipstein wrote...

Well, I could comment a bit on gravity waves vs. lasers.

Consider wavelength, and how that limits narrowness of a beam.

If I wanted to be noticed by someone on a planet 30 lightyears away,
I would get the biggest Nd:YAG ("YAG") laser that I could get and fire
it through a large telescope.

Let's see what happens if I get a 25 megawatt peak pulse YAG laser
(1064 nm) and fire it out a telescope whose objective is 3 meters in
diameter. I try Google and find 25 MW YAG lasers have been made, and
Earth's biggest telescope is about 5 meters last time I checked ...

Don, you can review Paul's take on the numbers at his oseti website.
http://seti.harvard.edu/oseti/ and http://seti.harvard.edu/oseti/allsky/

One working assumption, IIRC, is the transmitting end employs at least
MJ pulses, with a Keck-size telescope (10 meters). This would allow
detection to a 1000 light-year range, if the telescope is aimed at us
(the transmitted beam would spread out to the orbit of Jupiter). Some
calculations in a 1998 paper, http://seti.harvard.edu/oseti/tech.pdf
and a 1999 paper, http://seti.harvard.edu/oseti/bioast99_paper.pdf

One of Paul's students, Andrew Howard, has used the new all-sky oseti
telescope to take a quick look at a few million stars, a factoid he's
including in his PhD thesis-defense lecture, Thursday the 18th.

 

[Paul Hovnanian P.E.]

Don Klipstein wrote...

Don, you can review Paul's take on the numbers at his oseti website.
http://seti.harvard.edu/oseti/ and http://seti.harvard.edu/oseti/allsky/

One working assumption, IIRC, is the transmitting end employs at least
MJ pulses, with a Keck-size telescope (10 meters). This would allow
detection to a 1000 light-year range, if the telescope is aimed at us
(the transmitted beam would spread out to the orbit of Jupiter). Some
calculations in a 1998 paper, http://seti.harvard.edu/oseti/tech.pdf
and a 1999 paper, http://seti.harvard.edu/oseti/bioast99_paper.pdf

Or, for a sufficiently advanced civilization, its some kid with a laser
pointer he bought at the local WalMart.

;-)

 

[Don Lancaster]

I seriously doubt if anyone who has the power to communicate between star
systems would use electromagnetic radiation to do it. What's the status
on gravity waves these days? How about quantum black holes? ;-)

Thanks,
Rich

Has anyone noticed that the one frequency where everybody is listineng
to -- the water hole -- that it is ILLEGAL to transmit on anywhere in
this world.



--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[Winfield Hill]

Paul Hovnanian P.E. wrote...

Or, for a sufficiently advanced civilization, its some kid with
a laser pointer he bought at the local WalMart.

Hah! But one sobering thing is the power consumption involved.
I've read these lasers are no more than 10% efficient. If the
laser is fired at a slow rate of 10/sec, that's 10MW of light
emitted, and 100MW of continuous power drawn from the AC grid.
That's likely to be expensive in any civilization.

 

[Rich Grise]

Has anyone noticed that the one frequency where everybody is listineng
to -- the water hole -- that it is ILLEGAL to transmit on anywhere in
this world.

Huh? What freq. is that, and can you cite a statute or so?

Thanks,
Rich

 

[Keith]

Huh? What freq. is that, and can you cite a statute or so?

The "water hole" is from about 1420MHz (Hydrogen spectral line) to
1660MHz (Hydroxl line). I too would like to see the statute that
reserves a rather healthy chunk of a useful part of the spectrum.

According to the FCC:
http://www.fcc.gov/Bureaus/OPP/working_papers/oppwp38chart.pdf
this band is in the aeronautical and space telemetry and mobile
communications allocation. I don't see any thou shalt not trespass
designations, anyway.

 

[Jim Thompson]

The "water hole" is from about 1420MHz (Hydrogen spectral line) to
1660MHz (Hydroxl line). I too would like to see the statute that
reserves a rather healthy chunk of a useful part of the spectrum.

According to the FCC:
http://www.fcc.gov/Bureaus/OPP/working_papers/oppwp38chart.pdf
this band is in the aeronautical and space telemetry and mobile
communications allocation. I don't see any thou shalt not trespass
designations, anyway.

That is somewhat aged data. GPS _is_ authorized at ~1.6GHz.

...Jim Thompson

 

[Keith]

That is somewhat aged data. GPS _is_ authorized at ~1.6GHz.

Yes, it is a little old (2002), but GPS predates that. I'm
surprised GPS isn't in there, or perhaps it's part of
"radionavigation"?

Anyway, looking closer (blowing the chart up >200%), there is a
line in there from 1651 to 1660 (about the Hydroxyl line noted
above) that's listed as "Radio Astronomy, Space Research
(passive)".

....and I'll be danged, there is one at 1400-1427MHz too (a little
lower than the 1440 Hydrogen line) labeled "Earth Exploration-
Satellite(passive), Radio Astronomy, Space Research(passive)".

So, apparently there are legal EMI holes at these "two windows on
ET". Too bad Grease won't read this. Now he'll never figure out
how to phone home.

 

[Tim Auton]

Yes, it is a little old (2002), but GPS predates that. I'm
surprised GPS isn't in there, or perhaps it's part of
"radionavigation"?

GPS is in there; I presume Jim is referring to this note on page 8:
"The NTIA Manual (footnote G126) states that differential GPS stations
may be authorized in the 1559-1610 MHz band, but the FCC has not yet
addressed this footnote."

Presumably 'may be' is now 'is'.


Tim

 

[Keith]

GPS is in there; I presume Jim is referring to this note on page 8:
"The NTIA Manual (footnote G126) states that differential GPS stations
may be authorized in the 1559-1610 MHz band, but the FCC has not yet
addressed this footnote."

Ah, I see. Thanks.

 

[Jim Thompson]

GPS is in there; I presume Jim is referring to this note on page 8:
"The NTIA Manual (footnote G126) states that differential GPS stations
may be authorized in the 1559-1610 MHz band, but the FCC has not yet
addressed this footnote."

Presumably 'may be' is now 'is'.


Tim

The Garmin chip designs I did maybe 10-12 years ago, were 1.6GHz
receivers.

...Jim Thompson

 

[Joel Kolstad]

Jim,

The Garmin chip designs I did maybe 10-12 years ago, were 1.6GHz
receivers.

Times certainly have changed... I met some Garmin engineers at a job fair a
couple of years ago, and they said that -- at least for the handheld
receivers -- they no longer do custom chip design but use off-the-shelf parts.
I wonder if their aviation division still funds any custom IC designs?

 

[Jim Thompson]

Jim,



Times certainly have changed... I met some Garmin engineers at a job fair a
couple of years ago, and they said that -- at least for the handheld
receivers -- they no longer do custom chip design but use off-the-shelf parts.
I wonder if their aviation division still funds any custom IC designs?

That's odd. It's been less than a year ago that I was called in to
debug a processing issue.

However I do know that some companies, for instance Analog Devices, do
make general purpose RF chips.

...Jim Thompson

 

[Joel Kolstad]

That's odd. It's been less than a year ago that I was called in to
debug a processing issue.

Hmm... maybe it was really "handheld GPS receivers we develop at our local
plant here." (In particular, their higher-end newer handhelds use the
SiRFStar III chipset... see, e.g., http://www.gps.no/anm/templates/?a=977&z=2
..) In another 10 years or so perhaps you can tell us exactly which product it
is you worked on!

 

[Jim Thompson]

Hmm... maybe it was really "handheld GPS receivers we develop at our local
plant here." (In particular, their higher-end newer handhelds use the
SiRFStar III chipset... see, e.g., http://www.gps.no/anm/templates/?a=977&z=2
.) In another 10 years or so perhaps you can tell us exactly which product it
is you worked on!

I didn't know SiRF was supplying the chipsets to others ;-)

...Jim Thompson

 

[Michael A. Terrell]

So, apparently there are legal EMI holes at these "two windows on
ET". Too bad Grease won't read this. Now he'll never figure out
how to phone home.

He tried, but his home world refused to accept the collect charges on
his call.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida