Wok Your Way To The Center Of The Galaxy

October 6, 2023 by Dan Maloney 14 Comments

The round bottom of a proper wok is the key to a decent stir fry, but it also makes it hard to use on traditional Western stoves. That’s why many woks end up in a dark kitchen cabinet, unused and unloved. But wait; it turns out that the round bottom of a wok is the perfect shape for gathering something else — radio waves, specifically the 21-cm neutral hydrogen emissions coming from the heart of our galaxy.

Turning a wok into an entry-level radio telescope doesn’t appear to be all that hard, at least judging by what [Leo W.H. Fung] et al detail in their paper (PDF) on “WTH” or “Wok the Hydrogen.” Aside from the wok, which serves as the main reflector, you’ll need a bit of coaxial cable and some stiff copper wire to fashion a small dipole antenna and balun, plus some plastic tubing to support it at the focal point of the reflector. Measuring the wok’s shape and size, which in turn determines its focal point, is probably the hardest part of the build; luckily, the paper includes tips on doing just that. The authors address the controversy of parabolic versus spherical reflectors and arrive at the conclusion that for a radio telescope fashioned from a wok, it just doesn’t matter.

As for the signal processing chain, WTH holds few surprises. A Nooelec Sawbird+ H1 acts as preamp and filter for the 1420-MHz hydrogen line signal, which feeds into an RTL-SDR dongle. Careful attention is paid to proper grounding and shielding to keep the noise floor as low as possible. Mounting the antenna is a decidedly ad hoc affair, and aiming is as simple as eyeballing various stars near the center of the galactic plane — no need to complicate things.

Performance is pretty good: WTH measured the recession velocity of neutral hydrogen to within 20 km/s, which isn’t bad for something cobbled together from scrap. We’ve seen plenty of DIY hydrogen line observatories before, but WTH probably wins the “get on the air tonight” award.

Thanks to [Heinz-Bernd Eggenstein] for the tip.

The Wow! Signal And The Search For Extraterrestrial Intelligence

November 25, 2020 by Dan Maloney 53 Comments

On a balmy August evening in 1977, an enormous radio telescope in a field in the middle of Ohio sat silently listening to the radio universe. Shortly after 10:00 PM, the Earth’s rotation slewed the telescope through a powerful radio signal whose passage was noted only by the slight change in tone in the song sung every twelve seconds by the line printer recording that evening’s data.

When the data was analyzed later, an astronomer’s marginal exclamation of the extraordinarily powerful but vanishingly brief blip would give the signal its forever name: the Wow! Signal. How we came to hear this signal, what it could possibly mean, and where it might have come from are all interesting details of an event that left a mystery in its wake, one that citizen scientists are now looking into with a fresh perspective. If it was sent from a region of space with habitable planets, it’s at least worth a listen.

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Hackaday Links: October 18, 2020

October 18, 2020 by Dan Maloney 2 Comments

Remember subliminal advertising? The idea was that a movie theater operator would splice a single frame showing a bucket of hot buttered popcorn into a movie, which moviegoers would see and process on a subconcious level and rush to the concession stand to buy the tub o’ petrochemical-glazed starch they suddenly craved. It may or may not work on humans, but it appears to work on cars with advanced driver assistance, which can be spoofed by “phantom street signs” flashed on electronic billboards. Security researchers at Ben Gurion University stuck an image of a stop sign into a McDonald’s ad displayed on a large LCD screen by the side of the road. That was enough to convince a Tesla Model X to put on the brakes as it passed by the sign. The phantom images were on the screen anywhere from an eighth of a second to a quarter second, so these aren’t exactly subliminal messages, but it’s still an interesting attack that bears looking into. And while we’re skeptical about the whole subliminal advertising thing in the first place, for some reason we really want a bacon cheeseburger right now.

Score one for the good guys in the battle against patent trolls. Mycroft AI, makers of open-source voice assistants, proudly announced their latest victory against what they claim are patent trolls. This appears to be one of those deals where a bunch of investors get together and buy random patents, and then claim that a company that actually built something infringes on their intellectual property. Mycroft got a letter from one such entity and decided to fight it; they’ve won two battles so far against the alleged trolls and it looks pretty good going forward. They’re not pulling their punches, either, since Mycroft is planning to go after the other parties for legal expenses and punitive damages under the State of Missouri’s patent troll legislation. Here’s hoping this sends a message to IP squatters that it may not be worth the effort and that their time and money are better spent actually creating useful things.

Good news from Mars — The Mole is finally completely buried! We’ve been following the saga of the HP³, or “Heat Flow and Physical Properties Package” aboard NASA’s Mars InSight lander for quite a while. The self-drilling “Mole”, which is essentially the guts of an impact screwdriver inside a streamlined case, has been having trouble dealing with the Martian regolith, which is simultaneously too soft to offer the friction needed to keep the penetrator in its hole, but also too hard to pierce in places where there is a “duricrust” of chemically amalgamated material below the surface. It took a lot of delicate maneuvers with the lander’s robotic arm to get the Mole back on track, and it’s clearly not out of the woods yet — it needs to get down to three meters depth or so to do the full program of science it was designed for.

If watching Martian soil experiments proceed doesn’t scratch your itch for space science, why not try running your own radio astronomy experiments? Sure, you could build your own radio telescope to do that, but you don’t even have to go that far — just log into PICTOR, the free-to-use radio telescope. It’s a 3.2-m parabolic dish antenna located near Athens, Greece that’s geared toward hydrogen line measurements of the galaxy. You can set up an observation run and have the results mailed back to you for later analysis.

Here’s a fun, quick hack for anyone who hates the constant drone of white noise coming from fans. Build Comics apparently numbers themselves among that crowd, and decided to rig up a switch to turn on their fume extractor only when the soldering iron is removed from its holder. This hack was executed on a classic old Weller soldering station, but could easily be adapted to Hakko or other irons

And finally, if you’ve never listened to a Nobel laureate give a lecture, here’s your chance. Andrea Ghez, co-winner of the 2020 Nobel Prize in physics for her work on supermassive black holes, will be giving the annual Maria Goeppert Mayer lecture at the University of Chicago. She’ll be talking about exactly what she won the Nobel for: “The Monster at the Heart of Our Galaxy”, the supermassive black hole Sagittarius A*. We suspect the talk was booked before the Nobel announcement, so in normal times the room would likely be packed. But one advantage to the age of social distancing is that everything is online, so you can tune into a livestream of the lecture on October 22.

Probe The Galaxy On A Shoestring With This DIY Hydrogen-Line Telescope

September 29, 2019 by Dan Maloney 6 Comments

Foil-lined foam insulation board, scraps of lumber, and a paint-thinner can hardly sound like the tools of a radio astronomer. But when coupled with an SDR, a couple of amplifiers, and a fair amount of trial-and-error tweaking, it’s possible to build your own hydrogen-line radio telescope and use it to image the galaxy.

As the wonderfully named [ArtichokeHeartAttack] explains in the remarkably thorough project documentation, the characteristic 1420.4-MHz signal emitted when the spins of a hydrogen atom’s proton and electron flip relative to each other is a vital tool for exploring the universe. It lets you see not only where the hydrogen is, but which way it’s moving if you analyze the Doppler shift of the signal.

But to do any of this, you need a receiver, and that starts with a horn antenna to collect the weak signal. In collaboration with a former student, high school teacher [ArtichokeHeartAttack] built a pyramidal horn antenna of insulation board and foil tape. This collects RF signals and directs them to the waveguide, built from a rectangular paint thinner can with a quarter-wavelength stub antenna protruding into it. The signal from the antenna is then piped into an inexpensive low-noise amplifier (LNA) specifically designed for the hydrogen line, some preamps, a bandpass filter, and finally into an AirSpy SDR. GNURadio was used to build the spectrometer needed to determine the galactic rotation curve, or the speed of rotation of the Milky Way galaxy relative to distance from its center.

We’ve seen other budget H-line SDR receiver builds before, but this one sets itself apart by the quality of the documentation alone, not to mention the infectious spirit that it captures. Here’s hoping that it finds its way into a STEM lesson plan and shows some students what’s possible on a limited budget.