Author Topic: Strange radio bursts from space. ET?  (Read 11267 times)

Offline Kiwi

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Strange radio bursts from space. ET?
« on: May 14, 2015, 07:52:47 AM »
An intriguing story:--

On 31 March 2015 NewScientist published the following article,
Is this ET? Mystery of strange radio bursts from space
http://www.newscientist.com/article/mg22630153.600-is-this-et-mystery-of-strange-radio-bursts-from-space.html?full=true#

Quote
...says Hippke, "there is something really interesting we need to understand. This will either be new physics, like a new kind of pulsar, or, in the end, if we can exclude everything else, an ET."

Okay, but 31 March is just a little close to April Fool's Day, especially when times zones are taken into account.

Then on 11 May 2015, the Australian Morning Mail published this article,
Red Faces in Parkes
http://morningmail.org/28838/

Quote
Good grief, what exciting news. Maybe even extra-terrestrials? Is the science finally "in" on aliens? Not quite. That strange 'outer space' signal that baffled Australian scientists turns out to be microwave oven.

Is this a single leg-pull, a double, or really just a mistake?  :)
« Last Edit: May 14, 2015, 07:58:58 AM by Kiwi »
Don't criticize what you can't understand. — Bob Dylan, “The Times They Are A-Changin'” (1963)
Some people think they are thinking when they are really rearranging their prejudices and superstitions. — Edward R. Murrow (1908–65)

Offline Echnaton

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Re: Strange radio bursts from space. ET?
« Reply #1 on: May 14, 2015, 09:42:56 AM »
The writer for the Morning Mail certainly had a good laugh at the expense of the Parks guys.
The sun shone, having no alternative, on the nothing new. —Samuel Beckett


Offline ka9q

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Re: Strange radio bursts from space. ET?
« Reply #3 on: May 14, 2015, 07:24:59 PM »
I'm surprised they could be fooled so easily, and even more surprised that microwave ovens would be allowed at a radio astronomy site.

Microwave ovens and their radio properties are well known to radio hams and communication engineers. When the IEEE 802.11 (WiFi) group started work, microwave ovens were a major study topic as they would use the same 2.4 GHz frequency band.

Microwave ovens generate RF with a magnetron, a self-oscillating vacuum tube invented during World War 2 for radar. Ovens invariably power them with an unfiltered "half wave voltage doubler", a circuit that produces a half sinewave pulse and then nothing for the next half cycle. This pulses the magnetron on and off 60 (or 50) times per second, with half of its time spent totally off. At any given instant a magnetron produces a fairly clean signal, but its frequency sweeps quite a bit as the supply voltage varies.

WiFi was designed with these properties in mind to resist interference. All the newer modes use OFDM, which spreads the data out across a range of channels with error correcting codes able to reconstruct one or more of those channels should they be hit by a microwave oven signal. There's also an optional feature to divide up data packets into short pieces that can be sent during the half-cycle intervals when the magnetron is completely off.

Sounds to me like Parkes could have benefited from having a ham or communications engineer on staff...

Offline Kiwi

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Re: Strange radio bursts from space. ET?
« Reply #4 on: May 15, 2015, 06:39:45 AM »
I'm surprised they could be fooled so easily, and even more surprised that microwave ovens would be allowed at a radio astronomy site...

Sounds to me like Parkes could have benefited from having a ham or communications engineer on staff...

Yes. Not being my field, I didn't know about the interference you mention, but my main two thoughts were:--

1. Why didn't the techies who deal with a radio telescope know all about the various forms of possible interference?

2.  Why would anyone who's bright enough to be going to university and/or operating a radio telescope do such a dumb thing as open a microwave oven before it turns itself off?

Even I know not to do that, and as the Morning Mail writer said:

Quote
Actually the microwave didn’t leak in a real sense, the scientists there opened the microwave when it was still running, thereby ignoring the first rule – read the bloody instructions. As it says on chainsaws, “Don’t try to stop chain with hands.”

It is on the cards that whoever opened it got a dose of microwaves on the nuts.

Here's another report about the explanation, dated 6 May 2015:--
http://www.abc.net.au/news/2015-05-05/scientists-discover-signals-being-sent-by-kitchen-microwave/6445570

« Last Edit: May 15, 2015, 07:02:08 AM by Kiwi »
Don't criticize what you can't understand. — Bob Dylan, “The Times They Are A-Changin'” (1963)
Some people think they are thinking when they are really rearranging their prejudices and superstitions. — Edward R. Murrow (1908–65)

Offline smartcooky

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Re: Strange radio bursts from space. ET?
« Reply #5 on: May 15, 2015, 08:48:05 AM »
2.  Why would anyone who's bright enough to be going to university and/or operating a radio telescope do such a dumb thing as open a microwave oven before it turns itself off?

Well, colour me surprised!! I routinely stop the microwave by opening the door because there is no "stop" button. The door handle is like a "flush" car door handle. The moment you lift the handle, the microwave stops, then you have to lift it up further before the door unlatches.
If you're not a scientist but you think you've destroyed the foundation of a vast scientific edifice with 10 minutes of Googling, you might want to consider the possibility that you're wrong.

Offline ka9q

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Re: Strange radio bursts from space. ET?
« Reply #6 on: May 15, 2015, 02:22:02 PM »
Same here -- I thought just about everyone stopped a microwave oven by just pulling the door. There are interlock switches that kill power to the magnetron before the door actually opens. Even if it didn't stop immediately, the door has to move a certain distance before there can be significant RF leakage.

You may have wondered about the window in the door. Openings in a conductive shield have to be an appreciable fraction of a wavelength to permit leakage. The window is metal with lots of small holes that are much smaller than a wavelength, so light can pass but not the RF from the magnetron.

Ovens operate at 2450 MHz, which has a wavelength of about 13 cm. There's also a "quarter wave choke" built into the door's perimeter. It's usually covered by a plastic seal to keep dirt out, but it's basically a slot, 1/4 wavelength deep and electrically open on the other end so that it presents a short circuit at the plane of the door.

Offline Zakalwe

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Re: Strange radio bursts from space. ET?
« Reply #7 on: May 15, 2015, 02:27:21 PM »


2.  Why would anyone who's bright enough to be going to university and/or operating a radio telescope do such a dumb thing as open a microwave oven before it turns itself off?

Even I know not to do that, and as the Morning Mail writer said:

Quote
Actually the microwave didn’t leak in a real sense, the scientists there opened the microwave when it was still running, thereby ignoring the first rule – read the bloody instructions. As it says on chainsaws, “Don’t try to stop chain with hands.”

It is on the cards that whoever opened it got a dose of microwaves on the nuts.



Do you honestly think that a common or garden kitchen appliance that is present in millions of homes would be allowed on the market if the user got a blast of microwaves every time they opened the door during cooking? Really?

Look up "interlocks". They're the reason why your liver doesn't get cooked if you open a microwave or your feet don't get wet if you open a washing machine mid-cycle.
"The strain of anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that 'my ignorance is just as good as your knowledge.' " - Isaac Asimov

Offline BazBear

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Re: Strange radio bursts from space. ET?
« Reply #8 on: May 15, 2015, 05:19:44 PM »
This is a pretty funny story  :)

Anecdotal: I will say some microwave ovens I've been around can effect WiFi; if you hapen to be in the wrong (right?) place while the microwave is running. So, from my experience, there is at least some leakage from some of these devices that can even effect the performance of a technology designed with such interference in mind.
"It's true you know. In space, no one can hear you scream like a little girl." - Mark Watney, protagonist of The Martian by Andy Weir

Offline ka9q

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Re: Strange radio bursts from space. ET?
« Reply #9 on: May 15, 2015, 06:13:25 PM »
Oh, I'm sure they can. I haven't tried this recently, but a long time ago I took a spectrum analyzer home, stuck a small 1/4 wave antenna on it, and put it next to the microwave while I operated it. I could see a signal, but it wasn't that strong.

In our experience, 2.4 GHz cordless phones caused more interference to WiFi than microwave ovens. This is actually not much of a surprise; the phones are intentional radiators, and their proprietary broadband waveforms blanketed a large part of the band with interference.

WiFi is designed for cooperation not only among the stations on a given access point, but among stations on different networks that happen to share the same channel. Each physical layer message carries a field that says "I'm expecting a reply that will take X microseconds, everybody else please stay quiet until then". It's a modification of a scheme I invented circa 1990.

Moral: when buying a cordless phone, avoid the 2.4 GHz band or find one that uses WiFi or Bluetooth (which has features to minimize WiFi interference though I'm not familiar with them). There are also 'femtocells', small cellular base stations that you plug into your Internet connection to cover areas that might not be well covered by a carrier's base stations.
« Last Edit: May 15, 2015, 06:17:32 PM by ka9q »

Offline Kiwi

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Re: Strange radio bursts from space. ET?
« Reply #10 on: May 16, 2015, 01:54:34 PM »
...Do you honestly think that a common or garden kitchen appliance that is present in millions of homes would be allowed on the market if the user got a blast of microwaves every time they opened the door during cooking? Really?

No. Do you honestly think that I do?

I last used a microwave oven about 1986 or 1987, and because I knew then not to open the door when the magnetron was operating, I most likely learned it from strong warnings in an instruction book of earlier years. Which might indicate that it was easily done back then. Besides, they have no doubt evolved considerably since then.

Look up "interlocks"...

Please tell me why I should do that.  I was probably quite familiar with interlocks by 1962, by doing the sort of things that rural Kiwi teenagers did back then -- milking cows, operating high-speed cream separators and other machinery, ploughing paddocks, bringing in the hay, fiddling with engines, firearms and shanghais, sawing wood, travelling to sea in fishing boats, riding horses, building models, and dismantling and reassembling Bren Guns -- although I don't recall whether they actually had interlocks.

What I do recall is that two or three of the smartest cows in a herd of 40 figured out how to operate some of the simple mechanical interlocks that were used to inhibit their movements. So they also knew about them in the early 1960s.

Do you honestly think it would have been impossible to open the door of the microwave oven at Parkes while it was operating?  If so, perhaps you should take it up with Emily Petroff, the PhD student at Parkes, or Dr Simon Johnston, head of astrophysics at the Australian CSIRO,  the national science agency, because he apparently told the Guardian, "If you set it to heat and pull it open to have a look, it generates interference."

See this Guardian article dated 5 May 2015 for more information:
http://www.theguardian.com/science/2015/may/05/microwave-oven-caused-mystery-signal-plaguing-radio-telescope-for-17-years

Besides talking about modern interference from mobile phones, WiFi etc., that article says the microwave oven signals were most likely produced by maintenance staff, not astronomers, so I do apologise to the technical people for question 2 in post 4. I was misled by the Morning Mail article which says scientists were responsible.

I also get the impression from the Guardian that the articles linked in post 1 might be about two different subjects and that the Morning Mail writer might have confused the them, as often happens with technical matters.

1. The Guardian says the signals produced by the microwave oven were first detected in 1998, and known to be local, within 5km of the telescope.

2. It also says "Then on 1 January this year they installed a new receiver which monitored interference, and detected strong signals at 2.4 GHz, the signature of a microwave oven."

3. The Morning Mail mentions "11 bursts detected since 2007", and says they came from outer space, another galaxy, the cosmos, and possibly a new pulsar.

4. It also says
Quote
“Tests revealed that a [signal] can be generated at 1.4 GHz when a microwave oven door is opened prematurely and the telescope is at an appropriate relative angle,” Ms Petroff says in her paper.

So we have 2.4 and 1.4 GHz signals, and signals from outer space and signals that are known to be local.

The abstract in this paper:
http://arxiv.org/pdf/1504.02165v1.pdf
(which is mostly over my head) mentions both frequencies, the microwave oven, fast radio bursts (FRBs), and finishes with "...we furthermore demonstrate that the microwaves on site
could not have caused FRB 010724. This and other distinct observational differences show that FRBs are excellent candidates for genuine extragalactic transients." (My emphasis.)

Others here might understand the paper better than I, and it would be interesting to find if we do indeed have two different subjects here.
« Last Edit: May 16, 2015, 02:21:29 PM by Kiwi »
Don't criticize what you can't understand. — Bob Dylan, “The Times They Are A-Changin'” (1963)
Some people think they are thinking when they are really rearranging their prejudices and superstitions. — Edward R. Murrow (1908–65)

Offline smartcooky

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Re: Strange radio bursts from space. ET?
« Reply #11 on: May 17, 2015, 04:54:45 AM »
4. It also says
Quote
“Tests revealed that a [signal] can be generated at 1.4 GHz when a microwave oven door is opened prematurely and the telescope is at an appropriate relative angle,” Ms Petroff says in her paper.

So we have 2.4 and 1.4 GHz signals, and signals from outer space and signals that are known to be local.

I think interference around 1.4 GHz might be of real concern to certain radio astronomers, particularly cosmologists!

https://en.wikipedia.org/wiki/Hydrogen_line
If you're not a scientist but you think you've destroyed the foundation of a vast scientific edifice with 10 minutes of Googling, you might want to consider the possibility that you're wrong.

Offline ka9q

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Re: Strange radio bursts from space. ET?
« Reply #12 on: May 17, 2015, 08:00:40 AM »
1.4 GHz interference has been a problem for quite some time, mainly from nearby L-band transmitters with insufficient filtering.

I think the best place to do SETI is the far side of the moon. Not from its surface, but from lunar orbit; data can be taken on the far side, analyzed and dumped to earth during near side passes. Then it could look pretty much everywhere in the spectrum without interference from terrestrial or near-earth space sources, or from the atmosphere.