[David Schneider] asked himself, “How big a radio antenna would you need to observe anything interesting?” The answer turns out to be a $150 build of a half meter antenna. He uses it to detect the motions of the spiral arms of the Milky Way. The first attempt was a satellite TV dish and a cantenna feed, which didn’t work as the can wasn’t big enough to pick up signals at the 21cm wavelength of hydrogen emissions. Interstellar gas clouds are known to emit radio energy at this frequency.
Looking online, [David] tried aluminized foam board insulation, but was worried that the material didn’t seem to actually be conductive. A quick thrown-together Faraday cage with a cell phone didn’t seem to block any calls. Abandoning that approach, he settled on aluminum flashing used for roofing.
Continue reading “Roofing Radio Telescope Sees The Galaxy”
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.
People who enjoy radio are constantly struggling to find a place to erect a bigger and better antenna. Of course it’s a different story and the most hardcore end of the spectrum: radio astronomers. The Chinese are ready to open up a new radio telescope called FAST (Five-hundred-meter Aperture Spherical Radio Telescope). As the name implies, it is 500 meters in diameter which is about 1,600 feet — that five and a half American football fields or about four and half of the other kind of football field.
The new telescope will be the largest single-dish observatory in the world and will offer about twice the area of the next-largest single-dish instrument at Arecibo. The project is in a very remote location, presumably to reduce the level of local radio interference — it’s hard to find radio quiet zones in heavily populated areas.
Scientists hope the huge antenna will help solve the mystery of fast radio bursts and may even study exoplanets. In fact, earlier this year, the instrument detected hundreds of fast radio bursts from a source, many of which were too faint to be heard by lesser antennas. There are also plans to examine pulsars in an attempt to discover ripples in space-time. The location in the Dawodang depression of the Guizhou province uses about 4,400 panels and 2,000 mechanical winches to focus radio energy.
Other telescopes that use multiple dishes have more resolution and, in fact, FAST adds 3 dozen 5 meter commercial dishes to get an increase in resolution of 100 times. Of course, you could build your own, although to get up to 500 meters might be a stretch. If your backyard isn’t that big, you can build a tiny radio telescope too.
MIT is well known for rigorous courses, but they also have a special four-week term at the start of each year called the IAP — Independent Activities Period. This year, the MIT Radio Society had several interesting presentations on both the history and application of radio. You weren’t there? No problem, as the nine lecture were all recorded for you to watch at your leisure. You can see one of the nine, below.
These aren’t some five minute quicky videos, either. They are basically live captures that run anywhere from an hour to almost two hours in length. The topics are a great mix including radio history, software-defined radio, propagation, radio astronomy, RADAR, and even 5G.
You might have to pick and choose. Some of the lectures are suitable for just about anyone. Some assume a bit more radio expertise in electronics or math. Still, they are all worth at least a cursory skim to see if you want to really sit and watch in detail. The only nitpick is that some presenters used a laser pointer that doesn’t show up on the inset slide graphics in the video. That makes sense because the inset slides are not really in the room, but it can make it a little difficult to understand what the speaker is pointing to on a crowded slide.
Of course, if you want to dive deep and you need more background, MIT — along with many other institutions — will let you use their learning material for free. We were especially fans of the circuits class but there are many others including just raw materials from OCW.
Continue reading “MIT IAP Tackles Radio”
We are used to imagining radio telescopes as immense pieces of scientific apparatus, such as the Arecibo Observatory in Puerto Rico, or the Lovell telescope in the UK. It’s a surprise then that they can be constructed on a far more modest sale using off-the-shelf components, and it’s a path that [Gonçalo Nespral] has taken with his tiny radio telescope using a satellite dish. It’s on an azimuth-elevation mount using an Ikea lazy susan and a lead screw, and it has a satellite TV LNB at the hot end with a satellite finder as its detector.
So far he’s managed only to image the wall of his apartment, but that clearly shows the presence of the metal supporting structure within it. Taking it outdoors has however not been such a success. If we wanted to hazard a guess as to why this is the case, we’d wish to look at the bandwidth of that satellite finder. It’s designed to spot a signal from a TV broadcast bird over the whole band, and thus will have a bandwidth in the hundreds of MHz and a sensitivity that could at best be described as a bit deaf. We hope he’ll try a different path such as an RTL-SDR in the future, and we look forward to his results.
This isn’t the first simple radio telescope we’ve seen here, aside from at least one other LNB-based one we’ve also shown you a WiFi device.
Scientists don’t know exactly what fast radio bursts (FRBs) are. What they do know is that they come from a long way away. In fact, one that occurs regularly comes from a galaxy 3 billion light years away. They could form from neutron stars or they could be extraterrestrials phoning home. The other thing is — thanks to machine learning — we now know about a lot more of them. You can see a video from Berkeley, below. and find more technical information, raw data, and [Danielle Futselaar’s] killer project graphic seen above from at their site.
The first FRB came to the attention of [Duncan Lorimer] and [David Narkevic] in 2007 while sifting through data from 2001. These broadband bursts are hard to identify since they last a matter of milliseconds. Researchers at Berkeley trained software using previously known FRBs. They then gave the software 5 hours of recordings of activity from one part of the sky and found 72 previously unknown FRBs.
Continue reading “AI Finds More Space Chatter”
Radio waves are received on antennas, for which when the signal in question comes over a long distance a big reflector is needed. When the reception distance is literally astronomical, the reflector has to be pretty darn big. [The Thought Emporium] wants to pick up signals from distant satellites, the moon, and hopefully a pulsar. On the scale of home-built amateur radio, this will be a monstrous antenna. The video also follows the break.
In hacker fashion, the project is built on a budget, so all the parts are direct from a hardware store, and the tools are already in your toolbox or hackerspace. Electrical conduit, chicken wire, PVC pipes, wood blocks, and screws make up most of the structure so put away your crazy links to Chinese distributors unless you need an SDR. The form of the antenna is the crucial thing, and the shape is three perpendicular panels as seen in the image and video. The construction in the video is just a suggestion, but it doesn’t involve welding, so that opens it to even more amateurs.
Even if you are not trying to receive a pulsar’s signature, we have hacks galore for radios and antennas.
Continue reading “The Biggest Corner Antenna We’ve Ever Seen”