Mysterious Files PH

We’ve talked before about number stations — mysterious shortwave transmitters repeating numbers, presumably for clandestine purposes. But, of course, the mere fact that they are unusual makes them stand out. The best place to hide something is in plain sight. In the old days, a broadcaster might slip a fake news story in mentioning a name that has a secret meaning, for example. But according to [Steven Murdoch], the United States has an even more obvious hiding place for a numbers station: inside GPS.

Every L1 C/A navigation message is a 176-bit field known by the affectionate moniker: Subframe 4, Page 17. The GPS specification says it is for “special messages.” No one has disclosed what those messages might be.

[Murdoch] at University College London analyzed over 12 million GPS packets from 2007 to 2026, trying to understand what was in this field. You might think 176 bits isn’t much, and you are right. But the L1 C/A signal carries 50 bits per second, and each frame is 1,500 bits. As [Murdoch] points out: “every bit much earn its place.” Each subframe is 300 bits, so this mysterious signal is 12% of the subframe. It must be important to someone.

Even if you don’t find spy stuff that interesting, the techniques used to sift through 19 years of data using Python, Julia, and other tools are worth reading about. The source code is available, too.

In 2023, the field has, at least sometimes, changed format. However, the best guess is that the field is sending cryptographic rekeying to other systems.

Of course, the truth could be different, but you have to admit, hiding spy messages in the GPS stream is truly hiding in plain sight. Of course, there are still contemporary traditional number stations out there, too.

Although desalination is very commonly used these days to convert seawater into fresh water, one of the major disadvantages of current approaches is that commercial desalination plants produce a lot of brine, which has to be dumped somewhere ideally without causing major environmental issues. A new solar-thermal method as demonstrated by [Luheng Tang] et al. was published in Light: Science and Applications, with accompanying PR article.

This method is claimed to require no pre-treatment or leave brine, using special panels that wick water across their surface and then use solar radiation to distill this water. This differs from previous similar methods through a special surface treatment that prevents build-up of salts which would require cleaning or replacement.

The salts and other contaminants that would normally end up in the brine slough off these cells and can then be further processed to recover everything from plain table salt to lithium as well as gold, uranium and other substances of interest that are prevalent in seawater.

So far these self-cleaning cells have been tested with water from a number of oceans with a claimed 74% solar-to-vapor conversion efficiency and nearly 100% salt extraction. As always the challenge will be in scaling this up to industrial levels, but so far it looks promising.

Christopher Nolan’s The Odyssey isn’t hitting theaters for another month or so, but if you’re already planning your trip to the cineplex, you may want to check out this page on the movie’s website which lets you view the trailer in the six (!) different formats it’s being released in.

We don’t really have an opinion on the big-screen adaptation of the epic tale as a piece of media, but from a technical standpoint, it’s interesting to see how the viewing experience changes between the 70mm IMAX version with an aspect ratio of 1.43:1 and the 35mm cut at 2.39:1. Unfortunately, the website offers no way to approximate what the movie will look like once compressed, streamed over the Internet, and displayed on a cheap TCL TV, to say nothing of how the viewing experience will be impacted should you watch the movie on your phone by way of a series of short YouTube clips while going to the bathroom. Maybe Nolan is saving that for his next film.

If you head over to the movies in one of Waymo’s vehicles, you can feel a little better about the long-term ecological impact of your trip thanks to a recently announced partnership between the autonomous car maker and B2U Storage Solutions. Under the agreement, old batteries pulled from Waymo’s fleet of self-driving electric cars will get a second life as localized grid storage.

The idea is that batteries which no longer hold enough charge to power a robo-taxi should still have enough capacity to store the energy produced by renewable sources so it can be doled out later when the demand goes up. By installing these batteries in the cities that Waymo actually operates their vehicles in, they don’t have to worry about shipping them around either — they can just yank them out of the car, and wire them right into the grid. Of course, eventually the batteries will be too cooked to adequately perform in this role as well, but this should give them a few more productive years before they get torn down and scrapped.

Speaking of scrapping, the Ladybird project has announced a pretty radical change for an open source project: as of Friday no public pull requests to the codebase will be accepted, and the only people who can make changes to the code will be the official maintainers. The license for the project isn’t changing, so folks are still free to create forks and modify the code of the scratch-built browser however they wish, but they’ll have to do so with the understanding that their changes will likely never get merged back upstream.

So why the change? You probably guessed it already: they are sick of people sending in patches developed with AI. We’ve talked about this issue previously, and the Ladybird devs are hardly the only ones struggling to separate the wheat from the vibecoded chaff. For what it’s worth, the announcement makes it clear that the team isn’t necessarily against the responsible use of AI in software development. Their concern stems more from the fact that AI lets anybody and everybody produce code that at least looks valid, and it makes it harder to figure out what’s good and worthy of inclusion and what should probably stay in somebody’s personal repo.

On the subject of software development, health-conscious free software aficionados will be excited to hear that the GNUtrition project hit version 0.33 on Friday. For those keeping track, the free-as-in-speech tool for *nix nerds looking to keep track of their caloric intake hasn’t seen a major release since 2012. The update takes into account the latest US Department of Agriculture (USDA) dietary data, and somewhat surprisingly, switches the whole codebase from Python 2 to pure C. Patches which would have allowed the new build of GNUtrition to calculate the nutritional value of substances eaten off of one’s shoe were mysteriously vetoed from the highest levels of the Free Software Foundation.

One more software link for the road: assuming it hasn’t been taken down by Nintendo’s rabid lawyers by the time this hits the front page, check out this WebASM port of Pokemon Emerald that you can play right in the browser.

The game came out more than 20 years ago for the Game Boy Advance, so the fact that it can run in a modern browser isn’t exactly shocking given how much of today’s software lives on the web. But we still love seeing these decompilation efforts and all the hacks that are made possible once you’ve got the code to work from rather than having to emulate the original system.

Finally, the good folks at iFixit have released a video wherein they take apart fake Apple products that were purchased in the electronics wonderland of Shenzhen. As you might expect, the gadgets they picked up all look fairly convincing at arm’s length, but many of their features don’t actually work and their internals are cobbled together with random ill-fitting bits and bobs.

At the end of the video they do note that the knock-offs are in general easier to take apart than their Cupertino counterparts, but that this doesn’t really help with their repairability or long-term viability as you’ll likely have a hell of a time tracking down replacement parts for the Number 1 Best AirPoods Max.

See something interesting that you think would be a good fit for our weekly Links column? Drop us a line, we’d love to hear about it.

So you happen to have a gramaphone– maybe a big old Victrola/HMV, perhaps a Columbia– regardless of brand, it’s a big, beautiful conversation peice for your living room. It might not be the most practical listening device, since isnomuch as there is a vinyl renessance, it’s restricted to vinyl, not the old shellac 78s the these all-mechanical beasts were born for. [JGJMatt] decided to bring his gramophone into the 21st century, turning it into a bluetooth speaker without altering any of its original internals.

What’s really interesting is that this hack was once a commercial product– sort of. Back in the 1920s when everyone was listening to Jazz, the problem of ‘ what do I do with this massive gramophone cabinet when I’m not cutting a rug?’ was equally valid, and a solution was found: the Dulce-Tone Radio Speaker. A very weak speaker sits under the needle, turning the gramaphone mechanism into an amplifier for the radio. The very same concept, [JGJMatt] would work equally well in the 2020s with a bluetooth signal as in the 1920s with an AM one. There’s no demo video for this project, but you can hear how its 1920s inspiration sounded in the video below.

The driver for this device is made using a neodymium magnet and the voice coil from a 3W speaker. A 3D-printed needle-holder captures the gramophone’s needle– a much thicker and sturdier thing than the tiny diamond-tip you’d find on a modern turntable, we should note– and holds the magnet to it. The voice coil gets driven via a MH-M38 bluetooth module, and everything is held in a nice 3D-printed case along with the battery.

The hack is, of course, totally reversible: at any moment, you can remove the needle from this device and drop it on a 78 for some Jazz-era fun, or swap back for 21st century brainrot. If you happen to have some of those old shellac records and a modern turntable, note it takes more than the right RPM to get good sound.

It’s well known that the difference in executable size between a compiled binary and one hand-written in optimized assembler will be significant. The compiler brings in all manner of boilerplate whether it needs all of it or not, which is responsible for the extra space. [Weineng] has fallen down the rabbit hole of trying to make the smallest possible gcc-compiled C executable, and the resulting write-up is a fascinating read.

Surprisingly the smallest C program isn’t “Hello World”, but one which simply does nothing but return 0. This results in a binary weighing in at a surprisingly large 15,816 bytes — something which surely could be improved. There follows a set of clever compiler flags and bits of code manipulation to remove some debugging information, and strip out unnecessary stuff executed before void main().

At 13,632 bytes it’s still a little on the chunky side, so it’s time to examine what libraries it brings in. More compiler flags get it down to 8,704 bytes. Removing a code comment section and error handling with more flags takes it to 4,320 bytes. Then there’s code which dictates how memory is allocated, which brings it down to 400 bytes. That’s an impressive reduction!

Reading this as hardware people we maybe don’t have the elite knowledge of compiler flags it takes to manage something like this. But we’ve all at times had to reduce the size of a bit of software, so we’re sure some of the techniques used are going to be interesting to quite a few readers.

After all, even hardware people need to trim the fat at times.

Although cryocoolers are capable of pretty impressive cooling, for many of them the underlying working principle is simple enough that you do not need any special skills or a big budget to make your own version. Take the Gifford-McMahon cryocooler for example, which works using nothing more than some kind of coolant gas and a piston in a cylinder that you can even 3D print, as demonstrated by [Hyperspace Pirate] in a recent video.

The lowest temperature reached across the two prototypes was only -84°C, but this was mostly due to some sub-optimal design choices, such as the use of regular air and a clear acrylic tube to get a good glimpse at the inner workings. The trickiest part of this type of cryocooler is probably that you need to move the piston containing the regenerator between both ends of the cylinder to get a cool and a hot side.

That particular problem was solved by using magnets to move the piston externally, which worked beautifully until the problem of using regular compressed air from the shop compressor caused massive ice formation that jammed up the piston. Obviously this was not an unexpected issue, and for the next step the coolant gas will be replaced by helium, as making that gas freeze up requires quite a bit more effort.

A good demo, like [Linus Akesson]’s Sum Ergo Demonstrato, looks like magic to the average hacker. To normies who don’t know the limitations of the RP2350, they don’t see the big deal. To anyone who has spent any time with the chip, though, it’s a series of tricks you cannot help but be amazed by. Fortuanately for us, [Linus] isn’t actually a magician, because while a magician never reveals his tricks, [Linus] has an hour-long video explaining exactly how his demo was accomplished. We’ve embedded both the demo and the explanation below.

Even if you aren’t into YouTube, you should check out the demo video, and again– remember this is all on a Pi Pico with only the extra passives required for video-out. Then you can watch [Linus] explain how he did it, which is really best heard in his own words. There are a couple of bleeding-edge tricks on the RISC V core and peripherals that we would hate to misrepresent– especially the clever hack with the interpolator that he uses for 3D acceleration.

If this sounds a bit familiar, it’s because we were equally impressed by his Kaleidoscopico demo last year. From demos like this to 3D engines on the ESP32, its amazing what you can do on modern micros if you’re willing to hit the limits of the hardware.

Thanks to [Stephen Walters] for the tip!

The Demo:

Technical video: