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An Interesting SETI Candidate in Hercules

Posted: Tue Aug 30, 2016 1:22 am
by Carl White
An international team of researchers has announced the detection of “a strong signal in the direction of HD164595”.

Re: An Interesting SETI Candidate in Hercules

Posted: Tue Aug 30, 2016 3:49 am
by Tom Ligon
I'm not familiar with the signal scales and civilization levels they're citing, and I suspect most readers are even more in the dark.

When I wrote "Payback" for Analog a few years back, I collaborated with Dr. H. Paul Shuch of The SETI League, a group of amateur radioastronomers. Shuch uses the San Marino Scale, which he helped invent. The passage below illustrates it. The SETI League members turn old satellite dishes and ICOM digital microwave receivers into spectrum analyzers (the receivers can tune under computer control and can sweep the desired band). Supposedly, one of these rigs, with a 12-ft dish, could have picked up the "WOW" event, the strongest SETI candidate signal known so far. What they lack in sensitivity, they make up for in number.

Anyway, here's how you would attract the attention of an evil Emperor 20 LY away, and make him throw a Bussard Interstellar Ramjet Star-Killer your way:

>> Indira shook her head. “It is unlikely any of those would have been heard at Eta Cass. We’ve been mapping the Oort cloud with very powerful radar. The pings have been up in the terawatt range, in order to generate reflections off comets up to half a light-year away. The pings were focused into tight beams. We started doing it about seven or eight decades ago, and some of those studies were pointed right in their direction, weighing in at about a seven on the San Marino Scale."
"San Marino Scale?" Tuekakas followed her gaze to the constellation.
"That's the analytical tool used by the International Academy of Astronautics, to quantify the significance of transmissions from Earth. Developed by Almar and Shuch, way back in twenty-ought-something. Dr. Shuch was the original Dr. SETI, one of my hats these days."
"How easily detectible is a seven on this scale?"
"The landmark Arecibo message sent in 1974 was just slightly stronger," she replied. "If they had SETI gear set up and aimed at all the habitable nearby stars as we do, they’d have detected the signals easily.”

Re: An Interesting SETI Candidate in Hercules

Posted: Tue Aug 30, 2016 7:20 am
by 93143

Is there a type of stellar maser that produces a single peak at ~11 GHz?

Re: An Interesting SETI Candidate in Hercules

Posted: Tue Aug 30, 2016 3:16 pm
by Tom Ligon
How I got hooked up with the SETI League: I showed up at a Philadelphia SF convention in Nov 1998 with the little "Dog and Pony II" demo reactor. It was a big hit. Shuch was in the audience and took some pics which went on their website as "Picture of the Week", March 6 and 13, 1999. By that time, Shuch and company had rigged up their own dog and pony show demo radiotelescope to take to SF conventions, their March 20 pic of the week.

They don't yet have an article on this new signal. I was interested if any of their homebrew receivers are sensitive enough to pick it up. Here's the sort of equipment they run. The older receivers they use are sometimes found on e-bay for a few hundred dollars. That and an old "West Virginia Sunflower" satellite dish and supporting front-end electronics make a credible radiotelescope. One needs a larger ground station dish to have a chance at SETI signals.

1.3 –1.7 GHz Waterhole frequency coverage (but the receivers can be tuned to other bands than the water hole)

Sensitivity of 10^-23 Watts/m^2; 10 Hz DSP bins

The new signal is 750 mJy, or milliJanskys, a new unit for me. But if I'm reading the wiki right, a Jy is 10^-26 W/m^2/Hz, with Hz interpreted as bandwidth spread. The new signal is 0.75 Jy. This would put the amateur Argos receivers, running 10Hz bins, about a 3-4 orders of magnitude too insensitive to pick up this signal, whereas they would have gotten the WOW signal.

The strength of the amateur SETI approach is not sensitivity ... hard to compete with the Allen array. What the amateurs offer is number. The Allen array can only look at one tiny area of sky at a time, and with some bandwidth limitation (I think they run multiple receivers at once but you can't see the whole spectrum instantly). Plus the Allen array can only be used for SETI a tiny fraction of the time. The result it that its chance of detecting a signal is nearly zero.

The amateurs, by contrast, are only limited by the willingness of people to invest a few thousand bucks in a huge dish and some electronics, which they point to some band in the sky and let run and run and run, as they filter thru the false alarms without reward for year after year. The SETI League goal is 5000 such receivers. Lacking the sensitivity, they'd probably not detect anything but the evil aliens coming past the Moon. 50 kW television signals from 93 LY? Totally lost in the noise. It would have to be a very powerful and deliberate signal such as I had in my story, and the implications of that are ... chilling.

So, really, both approaches have almost the same chance of success, which may be around the same as me winning a billion dollar lottery.

But I do play big lotteries, and I have checked e-bay for a deal on an ICOM microwave receiver.

Re: An Interesting SETI Candidate in Hercules

Posted: Tue Aug 30, 2016 10:20 pm
by Tom Ligon
I wanted to compare this signal to the WOW! event, the strongest SETI candidate, August 15, 1977. It turns out the data on that are a bit messed up due to an alignment issue. The instrument used evidently had two horns, not quite tweaked together due to a setup error, and there is some uncertainty as to which was really getting the signal. But the analysis says they were either getting 54 or 212 Jy of signal. Either is considerably stronger than the new signal. The WOW! event also lasted longer.

The article goes in to the calculation of the signal flux, including just how they interpret the /Hz term. It appears that the receivers the amateurs are using, with 10Hz bins, may be considerably better than the Big Ear had (looking at a 10 kHz window). However, as anyone who has put in some quality time with a spectrum analyzer can tell you, there's always a trade off between tightening bandwidth resolution and scan rate. Do you want to scan a broad band, or do you want to resolve a sharp peak?

Re: An Interesting SETI Candidate in Hercules

Posted: Wed Aug 31, 2016 12:48 am
by kunkmiester

Re: An Interesting SETI Candidate in Hercules

Posted: Wed Aug 31, 2016 4:31 am
by Tom Ligon
I was just reading yesterday that they can generally distinguish satellites by Doppler shift when they pass by. It should be part of their normal protocol for verification.

The link below shows one graphical presentation of data from a passing satellite.