Arecibo shutdown...

[Steve Wilson]

Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:

On 20/11/2020 18:38, bob prohaska wrote:
Tom Del Rosso <fizzbintuesday@that-google-mail-domain.com> wrote:
Martin Brown wrote:

It is a shame to lose a grand old instrument even if it could only
look at a fraction of the sky around the zenith it was a *very* big
dish.

Something farther from the equator could scan a lot more sky even if
was also a stationary dish. Why did we put it in Puerto Rico?

Probably, cost. It\'s built into a natural cavity in the ground. I
believe the new Chinese instrument is constructed similarly.

An aside: Over what distance could two Arecibo-like instruments
communicate if A) they knew where to look and what to look for

A considerable distance although if you knew that much detail you
might well build a phased array to do it rather than use a single
dish.

B) they knew only where to look, but not what to look for

I\'m not sure how they could be in that position since to know where to
look someone would have had to tell them!

C) They knew not where to look and not what to look for
D) they knew not where to look, but did know what to look for

C&D are more or less the same problem and looking for stars where the
radio emissions are distinctly non-thermal, polarised and have
periodicities in the could be a frame rate zone of say 10-100 FPS
would be good hunting territory. It also coincides with naturally
occurring pulsars which when first detected at Cambridge were labelled
LGM on the chart recording!

In actuality the pulsar surveys look for stuff on a much wider range
than that since they don\'t know for sure what the ultimate bounds on
pulsar spin rates actually are.

https://en.wikipedia.org/wiki/PSR_B1919%2B21

Millisecond pulsars were missed until the kit and inspired data
processing improvements became good enough to see them.

https://en.wikipedia.org/wiki/PSR_B1937%2B21

Snag is that if we are any guide a civilisation will only be obviously
radio bright from the point where they can build high power
transmitters to the time when they master spread spectrum and fibre
technologies.

The answers doubtless depend on time allocated to the search.
Let\'s assume 50 years, the approximate life of the instrument.

I\'ve done a little web-surfing and found no explicit discussions.
The answers might have some bearing on Fermi\'s paradox.

I\'m not sure how far out an Arecibo class telescope could detect a
clone of itself if they were facing each other. The SETI guys have
given considerable thought to exactly what frequency(s) to transmit on
to get the greatest possible range and stand out as non-natural
emission.

The so called \"water hole\" is a favourite for SETI transmissions and
passive listening (on the assumption that all scientists think alike).

https://www.seti.org/seti-institute/project/details/seti-observations

A narrowband CW signal with near 100% linear polarisation pulsed in a
binary pattern will attract attention if seen by a scientist.
Somewhere in the window between 1 & 10GHz being probably the optimum
depending on the figure of the dish and the power of the transmitter.

I thought the hydrogen line at 1,420,405,751 Hz was the obvious choice:

https://en.wikipedia.org/wiki/Hydrogen_line



--
Science teaches us to trust. - sw

 

[Martin Brown]

On 21/11/2020 12:15, Rob wrote:

bitrex <user@example.net> wrote:
The reply from even a Type I civilization (which is far more advanced
than ours), that wished to communicate, would not be subtle when it
arrives. The ability of a civilization to pull signals out of the noise
and return the call massively amplified likely scales with the civilization.

If and when a civilization like that picks up our lil signal and they
decide they have something to say in response, when the reply come back
no one\'s going to be mistaking it for anything other than what it is.

You seem to assume that \"an advanced civilization\" means that it has
found how to defy the laws of nature. Or that has other laws of nature.

More that they can build a bigger amplifier and dish than we can dream
of - supposing that they choose to reply. Snag is that they might not
transmit for very long and if nothing sensitive enough is looking their
way we would still miss it even if it was a response to one of our signals.

Light travel time on a round trip for a msg is non trivial!

--
Regards,
Martin Brown

 

[server]

On Fri, 20 Nov 2020 18:38:35 -0000 (UTC), bob prohaska
<bp@www.zefox.net> wrote:

Tom Del Rosso <fizzbintuesday@that-google-mail-domain.com> wrote:
Martin Brown wrote:

It is a shame to lose a grand old instrument even if it could only
look at a fraction of the sky around the zenith it was a *very* big
dish.

Something farther from the equator could scan a lot more sky even if was
also a stationary dish. Why did we put it in Puerto Rico?

Probably, cost. It\'s built into a natural cavity in the ground. I believe
the new Chinese instrument is constructed similarly.

Arecibo has a more or less spherical reflector, so it doesn\'t give
perfect focus in any direction, but on he other hand, allows moving
the feed horn in a larger area and hence aim at different parts of the
sky.

Special feed horns has been used at least with other spherical
reflectors to improve the focus for instance with multiple feed horns
to receive multiple geosynchronous satellites.

The Chinese instrument modifies the surface of the reflector so that
is parabolic as viewed from the prime focus location, thus having
perfect focus.

An aside: Over what distance could two Arecibo-like instruments communicate if
A) they knew where to look and what to look for

According to
https://en.wikipedia.org/wiki/Search_for_extraterrestrial_intelligence#UCLA
420 light years.

B) they knew only where to look, but not what to look for
C) They knew not where to look and not what to look for
D) they knew not where to look, but did know what to look for

If only approximate direction is known (say with constellation
accuracy only) a phased array would be more suitable to create
multiple simultaneous beams in real time. It is just a question of
computational power to generate multiple narrow beams.

 

[Martin Brown]

On 20/11/2020 12:53, Tom Del Rosso wrote:

Martin Brown wrote:

Taking potshots at nearby F,G,K type stars is a much better bet iff we
want to be noticed as non-thermal radiation. For the period where we
had high power radars and analogue TV we were obvious to anyone
looking for interesting signals with a sensitive enough radio
telescope.

The change to digital TV will be misinterpretted somewhere, someday, as
the end of our civilisation, when in fact it was the beginning of a new
era of reruns from TV\'s golden age.

Alien reptiles intending to colonise the Earth and destroy US democracy
clearly based their skin suits on that weird pale orange skin tone that
US TV newscasters were clamped to on their approach the Earth.

The orange panda effect is surprisingly prominent on one such example!

It would have been more obvious if their skin flickered eerily between
pale purple and sickly green like on the earliest NTSC transmissions.

--
Regards,
Martin Brown

 

[Martin Brown]

On 22/11/2020 12:18, Steve Wilson wrote:

Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:

The so called \"water hole\" is a favourite for SETI transmissions and
passive listening (on the assumption that all scientists think alike).

https://www.seti.org/seti-institute/project/details/seti-observations

A narrowband CW signal with near 100% linear polarisation pulsed in a
binary pattern will attract attention if seen by a scientist.
Somewhere in the window between 1 & 10GHz being probably the optimum
depending on the figure of the dish and the power of the transmitter.

I thought the hydrogen line at 1,420,405,751 Hz was the obvious choice:

https://en.wikipedia.org/wiki/Hydrogen_line

Not really since although you can be pretty sure that radio astronomers
will be looking at that line in detail there is a heck of a lot of
neutral hydrogen in the galaxy so an artificial signal will be buried by
the natural emmissions from the galactic medium. The \"water hole\" is
between that line and the higher OH line at 1720MHz - bounded by H...OH
frequencies.

If you wanted to stand out you transmit at high power on a non-natural
frequency just far enough away to be at an insane Doppler shift but
still well within the likely front end bandwidth of a receiver.

--
Regards,
Martin Brown

 

[Martin Brown]

On 21/11/2020 19:04, upsidedown@downunder.com wrote:

On Sat, 21 Nov 2020 18:01:11 -0000 (UTC), bob prohaska
bp@www.zefox.net> wrote:

upsidedown@downunder.com wrote:

The Friis equations
https://en.wikipedia.org/wiki/Friis_transmission_equation tells the
expected received power, when both antenna aperture areas, distance
between antennas and wavelength is known.


There doesn\'t seem to be any consideration of either self-noise in
the receiver, nor background noise in the environment in Friis formula.
Those would seem to be the limiting constraints in the distance at
which two Arecibo-like instruments could recognize one another. The
receiving instrument must be able to detect the sender above both
its own self-noise and the background emissions.

Perhaps the question becomes one of \"how noisy is the universe\" rather
than \"how quiet/sensitive is the best receiver\"....

The Big Bang 4 K radiation is an issue, since it comes from all
directions. The 4 K black body radiation has the peak around 1 mm, so
this affects the microwave reception.

The quietest part of the radio spectrum is 1GHz to 10GHz carefully
avoiding the obvious neutral H and OH molecular emission lines. Higher
than that the microwave background swamps you and at lower frequencies
everything in the universe is a thermal radio emitter mostly getting
brighter as frequency decreases.

For shorter wavelengths, the question is how many warm/hot objects
are in the beam width. Ordinary stars do not radiate much in the far
UV.

Photons above the UV Lyman alpha line do not get far before they
encounter an atom of neutral hydrogen to ionise and get scattered and/or
re-emitted isotropically in that rest frame. It leaves a signature of
absorption lines in the light from the most distant objects.

http://www.astro.ucla.edu/~wright/Lyman-alpha-forest.html

--
Regards,
Martin Brown

 

[John S]

On 11/22/2020 8:25 AM, Martin Brown wrote:

On 21/11/2020 19:04, upsidedown@downunder.com wrote:
On Sat, 21 Nov 2020 18:01:11 -0000 (UTC), bob prohaska
bp@www.zefox.net> wrote:

upsidedown@downunder.com wrote:

The Friis  equations
https://en.wikipedia.org/wiki/Friis_transmission_equation tells the
expected received power, when both antenna aperture areas, distance
between antennas and wavelength is known.


There doesn\'t seem to be any consideration of either self-noise in
the receiver, nor background noise in the environment in Friis formula.
Those would seem to be the limiting constraints in the distance at
which two Arecibo-like instruments could recognize one another. The
receiving instrument must be able to detect the sender above both
its own self-noise and the background emissions.

Perhaps the question becomes one of \"how noisy is the universe\" rather
than \"how quiet/sensitive is the best receiver\"....

The Big Bang 4 K radiation is an issue, since it comes from all
directions. The 4 K black body radiation has the peak around 1 mm, so
this affects the microwave reception.

The quietest part of the radio spectrum is 1GHz to 10GHz carefully
avoiding the obvious neutral H and OH molecular emission lines. Higher
than that the microwave background swamps you and at lower frequencies
everything in the universe is a thermal radio emitter mostly getting
brighter as frequency decreases.

For shorter wavelengths, the question is how many warm/hot  objects
are in the beam width. Ordinary stars do not radiate much in the far
UV.

Photons above the UV Lyman alpha line do not get far before they
encounter an atom of neutral hydrogen to ionise and get scattered and/or
re-emitted isotropically in that rest frame. It leaves a signature of
absorption lines in the light from the most distant objects.

http://www.astro.ucla.edu/~wright/Lyman-alpha-forest.html

Paul Horowitz went into detail about this:

https://www.youtube.com/watch?v=sImBlq542TQ

A Laser seems to be the best choice.

 

[Tom Del Rosso]

Martin Brown wrote:

On 20/11/2020 13:01, Tom Del Rosso wrote:
Martin Brown wrote:

It is a shame to lose a grand old instrument even if it could only
look at a fraction of the sky around the zenith it was a *very* big
dish.

Something farther from the equator could scan a lot more sky even if
was also a stationary dish. Why did we put it in Puerto Rico?

The stripe of sky you can see varies with latitude like Cos(latitude)
so near the equator is about as good as you can get for maximising
utility. I think that finding a crater with almost the right shape
played a part.
Think about what would happen at the pole...

That\'s exactly what I thought of when I realized I had it backwards.

 

[Phil Hobbs]

On 11/22/20 8:53 AM, upsidedown@downunder.com wrote:

On Fri, 20 Nov 2020 18:38:35 -0000 (UTC), bob prohaska
bp@www.zefox.net> wrote:

Tom Del Rosso <fizzbintuesday@that-google-mail-domain.com> wrote:
Martin Brown wrote:

It is a shame to lose a grand old instrument even if it could only
look at a fraction of the sky around the zenith it was a *very* big
dish.

Something farther from the equator could scan a lot more sky even if was
also a stationary dish. Why did we put it in Puerto Rico?

Probably, cost. It\'s built into a natural cavity in the ground. I believe
the new Chinese instrument is constructed similarly.

Arecibo has a more or less spherical reflector, so it doesn\'t give
perfect focus in any direction, but on he other hand, allows moving
the feed horn in a larger area and hence aim at different parts of the
sky.

Special feed horns has been used at least with other spherical
reflectors to improve the focus for instance with multiple feed horns
to receive multiple geosynchronous satellites.

The Chinese instrument modifies the surface of the reflector so that
is parabolic as viewed from the prime focus location, thus having
perfect focus.

An aside: Over what distance could two Arecibo-like instruments communicate if
A) they knew where to look and what to look for

According to
https://en.wikipedia.org/wiki/Search_for_extraterrestrial_intelligence#UCLA
420 light years.

Of course the instrument has to last that long.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[David Lesher]

\"Tom Del Rosso\" <fizzbintuesday@that-google-mail-domain.com> writes:

Something farther from the equator could scan a lot more sky
even if was also a stationary dish. Why did we put it in Puerto
Rico?

It was too hard to move the bowl it is built in somewhere else.


--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that\'s close..........................
Unless the host (that isn\'t close).........................pob 1433
is busy, hung or dead....................................20915-1433

 

[bob prohaska]

John S <Sophi.2@invalid.org> wrote:

Paul Horowitz went into detail about this:

https://www.youtube.com/watch?v=sImBlq542TQ

A Laser seems to be the best choice.

A very interesting lecture. Thanks for posting the link!

One of the post-lecture questions asks \"at what distance
could we detect ourselves?\". It appears the answer is only
a few tens of light years. That\'s not quite what I was
asking, but it gives the perspective I wanted. Practically,
it seems we\'re very nearly blind.

Thanks for reading,

bob prohaska

 

[David Lesher]

Sam Harris is likely turning over in his grave.

Sam, W1FZJ, was famous for his VHF/UHF work. He was the East
Coast half of the first 1296 MHz moonbounce.

He would build large arrays, such as square quad of 432 MHz
yagis. Then he would build 3 more, ergo a quad of quads. He
lived in New England and was famous for \"If your antenna stays
up all winter, it\'s not big enough....\"

When he retired, it was to Puerto Rico. He was invited to
come help at Arecibo. He looked at all the small things the
million-dollar consultants didn\'t; such as coax connectors. The
first 2 weeks he was there, he bettered their S/S+N figure by
2 dB.

A toast to both him and Arecibo....

--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that\'s close..........................
Unless the host (that isn\'t close).........................pob 1433
is busy, hung or dead....................................20915-1433

 

[Bill Sloman]

On Saturday, November 21, 2020 at 12:42:38 PM UTC+11, Tom Del Rosso wrote:

bitrex wrote:
On 11/20/2020 7:53 AM, Tom Del Rosso wrote:
Martin Brown wrote:

Taking potshots at nearby F,G,K type stars is a much better bet iff
we want to be noticed as non-thermal radiation. For the period
where we had high power radars and analogue TV we were obvious to
anyone looking for interesting signals with a sensitive enough radio
telescope.

The change to digital TV will be misinterpretted somewhere, someday,
as the end of our civilisation, when in fact it was the beginning of
a new era of reruns from TV\'s golden age.



If the Galaxy is the size of one of Trump\'s mansions humanity has
effectively searched a postage-stamp sized area in one of the toilet
bowls for other residents
You don\'t like our part of the galaxy? You\'d rather be closer to the
black hole?

BTW Biden has several mansions too; he just didn\'t earn them by building
anything.

Neither did Donald Trump. His unique selling point is a very rich and successful father.

--
Bill Sloman, Sydney

 

[Bill Sloman]

On Saturday, November 21, 2020 at 11:16:05 PM UTC+11, Rob wrote:

bitrex <us...@example.net> wrote:
The reply from even a Type I civilization (which is far more advanced
than ours), that wished to communicate, would not be subtle when it
arrives. The ability of a civilization to pull signals out of the noise
and return the call massively amplified likely scales with the civilization.

If and when a civilization like that picks up our lil signal and they
decide they have something to say in response, when the reply come back
no one\'s going to be mistaking it for anything other than what it is.
You seem to assume that \"an advanced civilization\" means that it has
found how to defy the laws of nature. Or that has other laws of nature.

Not exactly. They will probably exploit different laws of nature.

High power lasers weren\'t a plausible mode of interstellar communication when Arecibo started up.

Niven and Pournelle\'s \"Mote in Gods Eye\" speculates about that. Jerry Pournelle is a meat-head, but Larry Niven always did his homework.
It wasn\'t intended as interstellar communication ... it was merely a side effect of launching an interstellar probe.

--
Bill Sloman, Sydney

 

[bilou]

On 20/11/2020 21:20, bitrex wrote:

The reply from even a Type I civilization (which is far more advanced
than ours), that wished to communicate, would not be subtle when it
arrives.

A replay of the original signal would seems a good start.

 

[Martin Brown]

On 20/11/2020 11:33, Steve Wilson wrote:

Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:

It is a shame to lose a grand old instrument even if it could only
look at a fraction of the sky around the zenith it was a *very* big
dish.

+1. Thanks

Sadly it has just got a whole lot worse.

The feed gantry fell to the ground overnight smashing the big dish and
it is now just a heap of rubble and twisted metal.

Dust still in the air in these recent Twitter images from the site.

https://twitter.com/JohnMoralesNBC6/status/1333753977196994560?ref_src=twsrc%5Egoogle%7Ctwcamp%5Eserp%7Ctwgr%5Etweet

and

https://twitter.com/DeborahTiempo

A very sad end to major radio telescope.

--
Regards,
Martin Brown

 

[Jan Panteltje]

On a sunny day (Tue, 1 Dec 2020 16:56:36 +0000) it happened Martin Brown
<\'\'\'newspam\'\'\'@nonad.co.uk> wrote in <rq5sk3$1r73$1@gioia.aioe.org>:

On 20/11/2020 11:33, Steve Wilson wrote:
Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:

It is a shame to lose a grand old instrument even if it could only
look at a fraction of the sky around the zenith it was a *very* big
dish.

+1. Thanks

Sadly it has just got a whole lot worse.

The feed gantry fell to the ground overnight smashing the big dish and
it is now just a heap of rubble and twisted metal.

Dust still in the air in these recent Twitter images from the site.

https://twitter.com/JohnMoralesNBC6/status/1333753977196994560?ref_src=twsrc%5Egoogle%7Ctwcamp%5Eserp%7Ctwgr%5Etweet

and

https://twitter.com/DeborahTiempo

A very sad end to major radio telescope.

I have been wondering ever since they called it beyond repair
if it would not be possible to (and I think that is all there is you need at the focus point) put
the LNA (and cooling I presume) in a drone and have it hover using differential GPS in the exact position.
I have tried that with my drone, powered by 100 kHz few hundred volt via thin coax indefinitely.
Would not cost shit and can be setup in no time.
http://www.panteltje.com/pub/h501s_drone_remote_power_flight_test_1_IMG_6274.JPG
Note the thin coax from the drone over the fence to ground control
http://www.panteltje.com/pub/h501s_drone_remote_power_test_ground_control_1_IMG_6276.JPG
At several hundred volt current is low and you can use the same coax for the signal too.
The idea in my case was to get a long vertical antenna up, or a small 70 cm one.

I really do not see the use of hanging a whole house over a dish.
Accuracy with differential GPS is within some centimeters, but of course you could use lasers etc
and even cameras for position control.
Kids stuff.
It is a nice dish, old brains there?

 

[Phil Hobbs]

On 12/1/20 11:56 AM, Martin Brown wrote:

On 20/11/2020 11:33, Steve Wilson wrote:
Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:

It is a shame to lose a grand old instrument even if it could only
look at a fraction of the sky around the zenith it was a *very* big
dish.

+1. Thanks

Sadly it has just got a whole lot worse.

The feed gantry fell to the ground overnight smashing the big dish and
it is now just a heap of rubble and twisted metal.

Dust still in the air in these recent Twitter images from the site.

https://twitter.com/JohnMoralesNBC6/status/1333753977196994560?ref_src=twsrc%5Egoogle%7Ctwcamp%5Eserp%7Ctwgr%5Etweet


and

https://twitter.com/DeborahTiempo

A very sad end to major radio telescope.

Well, it saved the NSF some money for controlled demolition.

Infrastructure maintenance is like saving for retirement: important but
not urgent (until it\'s too late).

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Eli the Bearded]

In sci.electronics.design, Martin Brown <\'\'\'newspam\'\'\'@nonad.co.uk> wrote:
> Sadly it has just got a whole lot worse.

One thing that has puzzled me is why this is a thread in
sci.electronics.design when sci.electronics.repair is right over there.

The feed gantry fell to the ground overnight smashing the big dish and
it is now just a heap of rubble and twisted metal.

Might need some engineering repair, too, I guess.

Elijah
------
the bigger they are, the harder the fall

 

[legg]

On Thu, 19 Nov 2020 22:56:03 GMT, Steve Wilson <spam@me.com> wrote:

Arecibo has reached EOL.

https://arstechnica.com/science/2020/11/famed-arecibo-observatory-to-be-
decommissioned-in-wake-of-cable-breaks/

Arecibo workers seem rather lackadaisical about it all.

Why is nobody shouting \'incompetent gits\'?

Was there no maintenance budget?

Didn\'t an alarm go off after the first stress failure?

RL