Tiny Telescope For Simple Radio Astronomy

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.

Studying Airplane Radio Reflections With SDR

A property of radio waves is that they tend to reflect off things. Metal surfaces in particular act as good reflectors, and by studying how these reflections work, it’s possible to achieve all manner of interesting feats. [destevez] decided to have some fun with reflections from local air traffic, and was kind enough to share the results.

The project centers around receiving 2.3 GHz signals from a local ham beacon that have been reflected by planes taking off from the Madrid-Barajas airport. The beacon was installed by a local ham, and transmits a CW idenfication and tone at 2 W of power.

In order to try and receive reflections from nearby aircraft, [destevez] put together a simple but ingenious setup.

ADS-B data was plotted on a map and correlated with the received reflections.

A LimeSDR radio was used, connected to a 9 dB planar 2.4 GHz WiFi antenna. This was an intentional choice, as it has a wide radiation pattern which is useful for receiving reflections from odd angles. A car was positioned between the antenna and the beacon to avoid the direct signal overpowering reflected signals from aircraft.

Data was recorded, and then compared with ADS-B data on aircraft position and velocity, allowing recorded reflections to be matched to the flight paths of individual flights after the fact. It’s a great example of smart radio sleuthing using SDR and how to process such data. If you’re thirsty for more, check out this project to receive Russian weather sat images with an SDR.

[Thanks to Adrian for the tip!]

Help For High-Frequency Hobbyists

Dead-bug circuit building is not a pretty affair, but hey, function over form. We usually make them because we don’t have a copper circuit board available or the duty of making one at home is not worth the efforts and chemical stains.

[Robert Melville and Alaina G. Levine] bring to light a compromise for high-frequency prototypes which uses the typical FR4 blank circuit board, but no etching chemicals. The problem with high-frequency radio is that building a circuit on a breadboard will not work because there is too much added inductance and capacitance from the wiring that will wreak havoc on the whole circuit. The solution is not new, build your radio module on a circuit board by constructing “lands” over a conductive ground plane, where components can be isolated on the same unetched board.

All right, sometimes dead-bug circuits capture an aesthetic all their own, especially when they look like this and they do allow for a darned small package for one-off designs.

Buy A Baofeng While You Still Can? FCC Scowls at Unauthorized Frequency Transmitters

There was a time when a handheld radio transceiver was an object of wonder, and a significant item for any radio amateur to own. A few hundred dollars secured you an FM walkie-talkie through which you could chat on your local repeater, and mobile radio was a big draw for new hams. Thirty years later FM mobile operation may be a bit less popular, but thanks to Chinese manufacturing the barrier to entry is lower than it has ever been. With extremely basic handheld radios starting at around ten dollars and a capable dual-bander being yours for somewhere over twice that, most licencees will now own a Baofeng UV5 or similar radio.

The FCC though are not entirely happy with these radios, and QRZ Now are reporting that the FCC has issued an advisory prohibiting the import or sale of devices that do not comply with their rules. In particular they are talking about devices that can transmit on unauthorised frequencies, and ones that are capable of transmission bandwidths greater than 12.5 kHz.

We’ve reported before on the shortcomings of some of these radios, but strangely this news doesn’t concern itself with their spurious emissions. We’re guessing that radio amateurs are not the problem here, and the availability of cheap transceivers has meant that the general public are using them for personal communication without a full appreciation of what frequencies they may be using. It’s traditional and normal for radio amateurs to use devices capable of transmitting out-of-band, but with a licence to lose should they do that they are also a lot more careful about their RF emissions.

Read the FCC statement and you’ll learn they are not trying to restrict the sale of ham gear. However, they are insisting that imported radios that can transmit on other frequencies must be certified. Apparently, opponents of these radios claim about 1 million units a year show up in the US, so this is a big business. The Bureau warns that fines can be as high as $19,639 per day for continued marketing and up to $147,290 — we have no idea how they arrive at those odd numbers.

So if you’re an American who hasn’t already got a Baofeng or similar, you might be well advised to pick one up while you still can.

UV5-R image via PE1RQM

Submarine to Plane: Can You Hear Me Now? The Hydrophone Radar Connection

How does a submarine talk to an airplane? It sounds like a bad joke but it’s actually a difficult engineering challenge.

Traditionally the submarine must surface or get shallow enough to deploy a communication buoy. That communication buoy uses the same type of radio technology as planes. But submarines often rely on acoustic transmissions via hydrophones which is fancy-talk for putting speakers and microphones in the water as transmitters and receivers. This is because water is no friend to radio signals, especially high frequencies. MIT is developing a system which bridges this watery gap and it relies on acoustic transmissions pointed at the water’s surface (PDF warning) and an airplane with high-precision radar which detects the oscillations of the water.

The complexity of the described setup is mind-boggling. Right now the proof of concept is over short distances and was tested in a water tank and a swimming pool but not in open water. The first thing that comes to mind is the interference caused by waves and by aerosols from wind/wave interactions. Those challenges are already in the minds of the research team. The system has been tested to work with waves of 8 cm (16 cm measured peak to trough) caused by swimmers in the pool. That may not sound like much, but it’s about 100,000 times the surface variations being measured by the millimeter wave radar in order to detect the hydrophone transmissions. Add to that the effects of Doppler shift from the movement of the plane and the sub and you have a signal processing challenge just waiting to be solved.

This setup is very interesting when pitched as a tool for researching aquatic life. The video below envisions that transmitters on the backs of sea turtles could send communications to aircraft overhead. We love seeing these kinds of forward-thinking ocean research projects, like our 2017 Hackaday prize winner which is an open source underwater glider. Oceanic studies over long distances have been very difficult but we’re beginning to see a lot of projects chipping away at that inaccessibility.

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Touch Anything And Everything

Powering IoT devices is often a question of batteries or mains power, but in rare exceptions to this rule there is no power supply (PDF Warning). At the University of Wisconsin-Madison and the University of California, San Diego, researchers have gone the extra mile to make advanced backscatter devices, and these new tags don’t need the discrete components we have seen in previous versions. They are calling it LiveTag, and it doesn’t need anything aside from a layer of foil printed or etched on a flexible ceramic-PTFE laminate. PTFE is mostly seen in the RF sector as a substrate for circuit boards.

We have seen some of the wild creations with wifi backscatter that range from dials to pushbuttons. RF backscatter works by modulating the RF signals in which we are continuously swimming. Those radio waves power the device and disrupt the ambient signals, which disruption can be detected by a receiver. With a BOM that looks like a statement more than a list, integration with many devices becomes a cost-effective reality. Do not however broadcast important data because you cannot expect great security from backscatter.

[Via IEEE Spectrum]

Tesla Opens with Precomputed Key Fob Attack

This clever precomputation attack was developed by a group of researchers at KU Leuven in Belgium. Unlike previous key fob attacks that we’ve covered in the past which have been essentially relay attacks, this hack precomputes a ton of data, looks for a collision in the dataset, and opens the door. Here’s how it works.

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