gps

355 Articles

Transponder Mania

July 16, 2026 by 28 Comments

In order to not hit something, you generally need to know where that thing is. On land, the meager human eyesight tends to be sufficient. On the water, however, the prospects are more dangerous and complicated. So, technology is required to ensure safe ocean voyages in the form of the AIS transponder system. The off the shelf solutions tend to work quite well, but [peterantypas] was displeased with the commercial offerings, and built what appears to be the first open source AIS transponder called MAIANA.

Automatic Identification System (AIS) is a GPS tracking system designed for maritime applications. Broadly speaking, it broadcasts GPS and other data at intervals over VHF radio. AIS is what allows the precise tracking of vessels by authorities, and online hobbyists. AIS is also often received by other vessels to augment radar improving boat to boat collision safety.

Most commercial AIS transponders used by sailors are rather bulky, expensive, come with a large power budget. The MAIANA project avoids these pitfalls by being entirely self-contained. The RF portion is largely made up of a STM32L4 micro controller, a SI Labs Si4460 ISM RF chip, and a Quectel L76L-M33 with a Johansson ceramic chip antenna for GPS. With such simple hardware, the PCB is easily small enough to fit inside the antenna assembly.

This design eliminates the need for long runs of multiple shielded RF cables to a bulky transponder unit inside. Instead, a simple Ethernet cable is used to transfer data to and from the mast. Inside the boat, a USB decoder is used to pass the AIS data on to a PC. This whole setup is remarkably simple and reliable, with hundreds of units having been produced since the project’s start.

While this is the first full blown AIS transponder we have covered, we have seen other projects utilizing the protocol. We have also seen quite a number of projects with the aircraft equivalent, ADS-B.

Thanks [Bernerd] for the tip!

Positioning Without Satellites Or Base Stations

July 1, 2026 by 37 Comments

We’re all used to satellite navigation systems such as GPS or GLONASS, sheer magic in which the combination of a set of reference transmitters and super-accurate timing information can be used to calculate a position to an astounding precision. They had land based predecessors such as LORAN and Decca Navigator which worked in a similar fashion but with fixed land-based reference transmitters. Terra is an attempt to do the same thing without a network of dedicated transmitters, instead using FM broadcast transmitters as its fixed points.

This might seem like an impossible task without access to the transmitters, but they have a workaround using the Internet as a backhaul. Instead of transmitting their timing information like the systems mentioned above, they rely on a set of reference receivers sharing it online to the client’s receiver software. So far they have a demo running in Denver.

The interesting thing about this system is that it’s open-source, and requires only a relatively inexpensive software defined radio receiver and a computer to operate. Now anyone with a group of internet-connected friends to set up reference receivers can have their own positioning system, it’s no longer the exclusive preserve of governments. We like this idea, and we look forward to seeing it being tested more widely.

If you’d like to know where we’ve come from, we’ve taken a look at LORAN before.

How Airspeed Sensors Work

June 30, 2026 by 28 Comments

When you’re driving your car, you’re probably regularly looking at the speedometer to make sure you comply with the local speed limits. The method by which it works is simple enough: the rotation of the wheels is sent mechanically via a cable to a dial on the dash, or an electronic sensor counts the rotations of the drivetrain and an electronically-controlled needle or display shows the speed.

But what about if you were in an aircraft, and the wheels had nothing to do with how fast you were going? How would you even begin to measure speed? There are two ways: there’s a convenient solution to this problem rooted in simple fluid mechanics, and a far-more-complex modern solution. Today, we’ll explore how planes and helicopters are able to figure out how fast they’re going, by the old ways and the new.

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Increasing Local GPS Accuracy For A Small Robot

June 25, 2026 by 32 Comments

Even though GPS makes it possible for us to easily navigate around the planet in almost any vehicle we’d like, whether that’s a passenger vehicle, airplane, or cargo ship, it’s not really suitable for applications that require sub-meter accuracy. For that, some specialized hardware is needed, and [GreatScott!] shows us how to do it using a small robot as a platform.

The key to extremely accurate GPS signals in this case is using a receiver that supports real-time kinematic positioning (RTK). This type of system relies on a base station with a known position communicating with local mobile receivers to increase the precision of those mobile receivers by comparing the phase angle of the received signals. Of course these modules are much more expensive than the average standard GPS receiver, but for this kind of accuracy there is always a cost.

After getting a baseline accuracy of around two meters with a standard GPS receiver, [GreatScott!] installs the RTK GPS mobile receiver on a tracked robotic platform and a base station on a fence post. With the RTK system running, the limiting factor in accuracy became the robot’s steering system, as its turning radius and steering algorithms weren’t up to the task of hitting centimeter-sized targets out of the box.

But, as a proof-of-concept, it goes to show how accurate GPS can be as long as the right hardware is used, and for practical applications is good enough to mow a lawn with a robot or even do some amateur land surveying.

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Long-Theorized GPS Weakness Exploited On Large Scale

June 23, 2026 by 40 Comments

GPS has become fairly common in our everyday lives, not only able to pinpoint our locations on Earth but also as an incredibly accurate timekeeping method. But since these satellites are around 20,000 km above Earth, the received signals on the surface of the planet can be incredibly weak. This makes them prone to jamming and spoofing, a weakness of the technology that has long been known. Although attempts to mitigate these problems have been ongoing, there has recently been a large-scale attempt to interfere with these signals that put all mitigation efforts to the test.

One proposed way to improve resilience is to supplement existing GNSS systems with low-Earth-orbit navigation satellites. In this example, a company called Xona is using a satellite called Pulsar-0 that operates in low-Earth orbit (LEO) and provides positioning and timing signals that are around 100 times stronger than standard signals from GPS/GNSS satellites. It is able to receive GPS signals as well, ensuring the two systems agree on one another. And, because Pulsar’s navigation signals originate from LEO and are much stronger than conventional GNSS signals, Xona expects them to be significantly more resistant to jamming.

Beyond geopolitics, spoofing GPS has some applications in finding legendaries in Pokemon Go as well as making it fairly trivial to steal GPS-guided drones.

An In-Browser Visualizer For GPS Satellites

June 18, 2026 by 9 Comments

Billions of people use GPS on a daily basis, along with the various other satellite navigation systems available today. But few of us spend much time contemplating the fleet of satellites above us that actually makes the system work. [Robert Wolf] has, though, and he’s built a simple visualizer that displays just what those space birds are doing at any given time.

The visualizer runs right in the browser, and displays a cluster of GPS satellites in a 3D view around the Earth. The tool also offers a list of satellites and related data, including signal-to-noise ratio of the received signals from each one, and the ability to play back satellite positions from previous days. The satellite positions are captured from a GPS receiver that [Robert] operates in the UK.

The view isn’t global or complete, since the receiver can only see a certain number of satellites from its location, but it nevertheless gives an idea of where a subset of GPS satellites are flying above the globe. Depending on the selected view, it’s possible to see the satellites superimposed over the world map itself — or from a distant observer’s perspective, as if looking at the Earth from a distance, among other options.

If you’ve ever wanted an intuitive idea about where the GPS satellites live, this tool is a great way to understand it. We’ve also previously discussed the wide range of GPS alternatives that have been developed over the years. If you’ve got your own GPS hacks brewing in the home lab, don’t hesitate to let us know on the tipsline.

Spy Tech: The GPS Numbers Station

June 8, 2026 by 24 Comments

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 must earn its place.” Each subframe is 300 bits, so this mysterious signal is 12% of the subframe. It must be important to someone.

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