WSPR May Hold The Key To MH370 Final Position

April 24, 2021 by Jenny List 53 Comments

The disappearance of Malaysia Airlines flight MH370 after an unexplained course change sent it flying south over the Indian Ocean in March 2014 still holds the mystery of the wreck’s final location. There have been a variety of efforts to narrow down a possible search area over the years, and now we have news of a further angle from an unexpected source. It’s possible that the aircraft’s path could show up in radio scatter detectable as anomalously long-distance contacts using the amateur radio WSPR protocol.

WSPR is a low-power amateur radio mode designed to probe and record the radio propagation capabilities of the atmosphere. Transmit beacons and receiving stations run continuously, and all contacts however fleeting are recorded to an online database. This can be mined by researchers with an interest in the atmosphere, but in this case it might also provide clues to the missing airliner’s flightpath. By searching for anomalously long-distance WSPR contacts whose path crosses the expected position of MH370 it’s possible to spot moments when the aircraft formed a reflector for the radio waves. These contacts can then either confirm positions already estimated using other methods, or even provide further course points. It’s an impressive demonstration of the unexpected data that can lurk in a trove such as the WSPR logbook, and also that while messing about on the airwaves the marks we leave behind us can have more benefit than simply bragging rights over the DX we’ve worked.

If this WSPR business intrigues you, then have a read of the piece in our $50 Ham series about it.

Header: Laurent ERRERA from L’Union, France, CC BY-SA 2.0.

[via Southgate ARC]

LibreVNA Is A Quality Open Hardware Vector Network Analyser

April 22, 2021 by Jenny List 39 Comments

There was a time when a Vector Network Analyser or VNA was the type of instrument that cost as much as a very fancy car or even a small house. The advent of commodity semiconductors that perform at high RF frequencies coupled with microcontrollers powerful enough to handle the data acquisition and processing might not yet have put those high-perfomance instruments within reach, but at our end of the market it’s opened the possibilities for some useful yet affordable devices. A fresh contender comes from [Jankae], whose LibreVNA tops out at 6 GHz and shows some significant attention to design detail that puts it above some of the budget offerings.

At its heart is the versatile Si5351 multi-way clock generator, accompanied by a pair of MAX2871 phase-locked-loop chips for the higher frequency local oscillators. A switched bank of low-pass filters take care of local oscillator harmonics, and in the receive chain there are ADL5081 mixers feeding a dual conversion IF running at 70 MHz and then 300 kHz. Finally the ADCs are Microchip’s MCP3313, and all is kept in sync by an FPGA and an STM32G431 microcontroller. The main data proccessing is offloaded to a host computer, with a software package and GUI able to be compiled on Windows, Linux, and OSX.

The PCB shows the attention to detail, not least in the power supply arrangements, with every major component receiving its own regulator to ensure no RF makes it down the power rails. It’s clear that a properly made LibreVNA won’t be as cheap as some of its rivals, but we think the corresponding performance hike would make the extra cost worthwhile.

If VNAs are new to you, we covered an introduction from [W2AEW] a while back.

A Superheterodyne Receiver With A 74xx Twist

April 19, 2021 by Dan Maloney 32 Comments

In a world with software-defined radios and single-chip receivers, a superheterodyne shortwave radio might not exactly score high on the pizzazz scale. After all, people have been mixing, filtering, and demodulating RF signals for more than a century now, and the circuits that do the job best are pretty well characterized. But building the same receiver using none of the traditional superhet trappings? Now that’s something new.

In what [Micha] half-jokingly calls a “74xx-Defined Radio”, easily obtained discrete logic chips, along with some op-amps and a handful of simple components, take the place of the tuned LC circuits and ganged variable capacitors that grace a typical superhet receiver. [Micha] started by building an RF mixer out of a 74HC4051 analog multiplexer, which with the help of a 2N3904 phase splitter forms a switching mixer. The local oscillator relies on the voltage-controlled oscillator (VCO) in a 74HC4046 PLL, a chip that we’ve seen before in [Elliot Williams]’ excellent “Logic Noise” series. The IF filter is a simple op-amp bandpass filter; the demodulator features an op-amp too, set up as an active half-wave rectifier. No coils to wind, no capacitors to tune, no diodes with mysterious properties — and judging by the video below, it works pretty well.

It may not be the most conventional way to tune in the shortwave bands, but we always love the results of projects that are artificially constrained like this one. Hats off to [Micha] for the interesting trip down the design road less travelled.

Continue reading “A Superheterodyne Receiver With A 74xx Twist” →

The $50 Ham: A Simple WSPR Beacon

April 15, 2021 by Dan Maloney 27 Comments

I was having a chat recently with someone, and it surprised me that she had an amateur radio license. I suppose it shouldn’t have come as much of a surprise; after all, getting a ham radio license is a pretty common rite of passage in the life of a hardware hacker. I guess it surprised me because she’d never mentioned it in our past conversations, and as we talked about it, I learned why. “I got my license because I thought ham radio was about building radios, ” she said. “But it’s not.”

In a lot of ways, she is right about the state of ham radio. There was a time that building one’s own gear was as central to the hobby as getting on the air, and perhaps more so. Now, though, with radios as cheap as $30 and the whiz-bang gear that can make reaching out across the planet trivially easy, building your own radios has slipped down a few notches. But homebrewing is far from a dead art, and as we’ll see in this installment of “The $50 Ham”, a WSPR beacon for the HF bands is actually a fun and simple — and cheap — way for the homebrew-curious to get a taste of what it’s like to build your own transmitter.

Continue reading “The $50 Ham: A Simple WSPR Beacon” →

The Last Days Of The Wild West

April 10, 2021 by Elliot Williams 21 Comments

We loved it a few weeks ago when an international team of hackers managed to record and decode telemetry and images from SpaceX launches. And now it looks like SpaceX has started encrypting it all in response. Booo!

Decoding satellite and other space ship transmissions has been a great hacker pastime. Most recently, we’ve seen a group working on listening in to the Chinese Tianwen-1 Mars probe shortly after its launch, but listening to the Deep Space Network or even just decoding weather satellite broadcasts can give folks a reason to stretch their radio muscles.

We understand that SpaceX runs some contract missions for US gov’t agencies that don’t appreciate leaking info about their satellite’s whereabouts, but for non-secret missions, we don’t see the harm in letting the amateurs listen in over their shoulder. Maybe they’re doing it for PR reasons if/when something goes badly wrong?

Whatever the reasons, it’s a shame. Space has been open to hackers for a long time, knowingly in the case of amateur satellites, and unknowingly in the case of many other satellites which until the mid-90s had command channels that were unencrypted. (I’ll have to stick with “unnamed sources” on this one, but I do know a person who has rotated a satellite that he or she didn’t own.) There’s a lot to be learned by listening to signals from above, and while you can still decode weather satellite data yourself, it’s not quite as sexy as downloading images straight from a Falcon 9.

The cool hand for SpaceX to have played would have been to say “of course — we broadcast unencrypted as PR to our biggest fans” but it looks instead like they simply didn’t think that anyone would be listening in, and this caught them by surprise and they panicked. In 2021, with something as complicated as a space mission, that’s a little bit embarrassing. Anyway, to those of you who managed to get in before encryption, kudos!

Uplink System For High-Altitude Balloons

April 9, 2021 by Maya Posch 10 Comments

Most uses of high-altitude balloons are fairly simple: send balloon up, have it beam down measurements and images. While this is indeed straightforward, it is also very limiting. This is why [Dave Akerman] has been working on adding to the HAB balloons he regularly flies. This builds on the work [Dave] did back in 2015 with adding LoRa transceiver RF communication.

Since LoRa transceivers are by definition capable of bidirectional communication, this was very useful for adding simple but essential features such as retransmission of data in case e.g. part of some image or telemetry data is missing. Other interesting things one can do with bidirectional transmission include controlling individual balloons, and having them transmit or relay information between balloons.

A tricky thing which [Dave] describes in the blog post is making sure that both ends of the connection are actually listening using timing settings. The use of encryption is also strongly recommended, unless you want to risk someone hijacking your balloons. This has now all been implemented in the HAB Explora app for Android, as well as the application for Windows.

Header image: Antonino Vara, CC BY 4.0.

Fun While It Lasted, Falcon 9 Telemetry Now Encrypted

April 7, 2021 by Tom Nardi 56 Comments

A few weeks back we brought word that Reddit users [derekcz] and [Xerbot] had managed to receive the 2232.5 MHz telemetry downlink from a Falcon 9 upper stage and pull out some interesting plain-text strings. With further software fiddling, the vehicle’s video streams were decoded, resulting in some absolutely breathtaking shots of the rocket and its payload from low Earth orbit.

Unfortunately, it looks like those heady days are now over, as [derekcz] reports the downlink from the latest Falcon 9 mission was nothing but intelligible noise. Since the hardware and software haven’t changed on his side, the only logical conclusion is that SpaceX wasn’t too happy about radio amateurs listening in on their rocket and decided to employ some form of encryption.

Since this data has apparently been broadcast out in the clear for nearly a decade before anyone on the ground noticed, it’s easy to see this as an overreaction. After all, what’s the harm in a few geeks with hacked together antennas getting a peek at a stack of Starlink satellites? [derekcz] even mused that allowing hobbyists to capture these space views might earn the company some positive buzz, something Elon Musk never seems to get enough of.

Some of the images [derekcz] was able to capture from the Falcon 9

On the other hand, we know that SpaceX is actively pursuing more lucrative national security launch contracts for both the Falcon 9 and Falcon Heavy. For these sensitive government payloads, the normal on-screen telemetry data and space views are omitted from the company’s official live streams. It seems likely the Pentagon would be very interested in finding out how civilians were able to obtain this information, and a guarantee from SpaceX that the link would be encrypted for all future flights could have helped smooth things over.

At the end of the post [derekcz] echos a sentiment we’ve been hearing from other amateur radio operators recently, which is that pretty soon space may be off-limits for us civilians. As older weather satellites begin to fail and get replaced with newer and inevitably more complex models, the days of picking up satellite images with an RTL-SDR and a few lines of Python are likely numbered.