Cockpit of a Hawker Siddeley Trident with the moving map display

A Live Map Display In A 1960s Airliner

January 23, 2024 by Danie Conradie 4 Comments

We tend take GPS navigation for granted these days, so it’s easy to forget that it became only available in the last few decades. Aviation navigation used to be significantly more challenging, so how was the Hawker Siddeley Trident, a 1960s airliner, fitted with a live updating map display? In a fascinating dive into aviation history the British Airliner Collection has spun up an insightful article on the magic behind these moving map displays.

Without access to satellite navigation or advanced electronics, engineers had to get creative. Enter the Trident’s moving map display, a marvel of ingenuity that predated the GPS systems. Using a combination of Doppler radar and some clever mechanics, pilots could accurately determine their position without relying on any external signals.

The system makes use of four Doppler radar beams, arranged in what was known as the Janus array. This configuration corrected for errors caused by changes in altitude or wind drift, ensuring accurate ground speed readings. The movable antennas mounted under the cabin floor could adjust its orientation to maintain alignment with the actual direction of travel, calculating drift angle precisely. Combined with compass information and flight time from a known start point to to indicate the current position with a pointer on a rolled paper map. The system was well ahead of it’s time, and significantly easier to use and more accurate than the Decca radio navigation system in use at the time.

It’s mind boggling to see the solutions engineers came up with without much of the digital technology we take for granted today. Gyroscopes for inertial navigation, the cavity magnetron for radar and radial engines were all building blocks for modern aviation.

Thanks for the tip [poiuyt]!

A Homebrew GPS Correction System For DIY Land Surveying

January 12, 2024 by Dan Maloney 60 Comments

For those of you rushing to the comment section after reading the title to tell [Ben Dauphinee] that his DIY land surveying efforts are for naught because only a licensed surveyor can create a legally binding property description, relax — he already knows. But what he learned about centimeter-resolution GPS is pretty interesting, especially for owners of large rural properties like him.

[Ben]’s mapping needs are less rigorous than an official survey; he just wants to get the locations of features like streams and wood lines, and to get topographic elevations so that he has a general “lay of the land” for planning purposes. He originally engaged a surveyor for that job, but after shelling out $4,600 to locate a single property line, he decided to see what else could be done. Luckily, real-time kinematics, or RTK, holds the key. RTK uses a fixed GPS station to provide correction signals to a mobile receiver, called a rover. If the fixed station’s position is referenced to some monument of known position, the rover’s position can be placed on a map to within a couple of centimeters.

To build his own RTK system, [Ben] used some modules from SparkFun. The fixed station has an RTK breakout board and a multi-band GNSS antenna to receive positioning data, along with a Raspberry Pi to run the RTK server. An old iPhone with a prepaid SIM provides backhaul to connect to the network that provides correction data. [Ben]’s rover setup also came mainly from SparkFun, with an RTK Facet receiver mounted on a photographer’s monopod. Once everything was set up and properly calibrated, he was able to walk his property with the rover and measure locations to within 4 centimeters.

This was not an inexpensive endeavor — all told, [Ben] spent about $2,000 on the setup. That’s a lot, especially on top of what he already paid for the legal survey, but still a fraction of what it would have cost to have a surveyor do it, or to buy actual surveyor’s equipment. The post has a ton of detail that’s worth reading for anyone interested in the process of mapping and GPS augmentation.

Building A GPS Receiver From The Ground Up

January 2, 2024 by Bryan Cockfield 11 Comments

One of the more interesting facets of GPS is that, at least from the receiver’s point-of-view, it’s a fairly passive system. All of the information beamed down from the satellites is out in the ether, all the time, free for anyone on the planet to receive and use as they see fit. Of course you need to go out and buy a receiver or, alternatively, possess a certain amount of knowledge to build a circuit that can take those signals and convert them into something usable. Luckily, [leaning_tower] has the required knowledge and demonstrates it with this DIY GPS receiver.

This receiver consists of five separate circuit boards, all performing their own function. The first, a mixer board, receives the signal via an active antenna and converts it to a lower frequency. From there it goes to a second mixer and correlation board to compare the signal to a local reference, then a signal processing board that looks at this intermediate frequency signal to make sense of the data its seeing. Finally, an FPGA interfacing board ties everything together and decodes the information into a usable form.

Dealing with weak signals like this has its own set of challenges, as [leaning_tower] found out. The crystal oscillator had to be decapped and modified to keep from interfering with the GPS radio since they operated on similar frequencies. Even after ironing out all the kinks, the circuit takes a little bit of time to lock on to a specific satellite but with a second GPS unit for checking and a few weeks of troubleshooting, the homebrew receiver is up and running. It’s an impressive and incredibly detailed piece of work which is usually the case with sensitive radio equipment like GPS. Here’s another one built on a Raspberry Pi with 12 channels and a pretty high accuracy.

Hackaday Links: December 24, 2023

December 24, 2023 by Dan Maloney 10 Comments

Back near the beginning of the current Solar Cycle 25, we penned an article on what the whole deal is with solar cycles, and what could potentially lie in store for us as the eleven-year cycle of sunspot population developed. Although it doesn’t really come across in the article, we remember being somewhat pessimistic about things, thinking that Solar Cycle 25 would be somewhat of a bust in terms of increased solar activity, given that the new cycle was occurring along with other, longer-period cycles that tend to decrease solar output. Well, looks like we couldn’t have gotten that more wrong if we tried, since the Sun lashed out with a class X solar flare last week that really lit things up. The outburst came from a specific sunspot, number 3514, and clocked in at X2.8, the most powerful flare since just before the end of the previous solar cycle. To put that into perspective, X-class flares have a peak X-ray flux of 10^-4 watts/m², which when you think about it is a lot of energy. The flare resulted in a strong radio blackout; pretty much everything below 30 MHz was unusable for a while.

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Designing A PCB GPS Antenna From Scratch

October 18, 2023 by Donald Papp 14 Comments

These days, when it comes to GPS devices the antenna is typically part of the package. But what better opportunity for [Pepijn] to learn how to make a GPS antenna from scratch for a badge add-on?

A patch antenna is an antenna of a flat design, which [Pepijn] was going to put directly on a PCB. However, there was added complexity due to GPS being a circularly polarized signal, and that meant doing some research.

Sadly, nowhere did [Pepijn] encounter a straightforward reference design or examples, but in the end success came from going with a truncated corner patch antenna design and using simulation software to figure out exactly what dimensions were needed. (The openEMS free simulation software didn’t bring success, but the non-free Sonnet with a trial license did the trick.) The resulting PCB may not look particularly complex, but every detail matters in such designs.

KiCad handled the PCB CAD design but the prototype came from cutting the PCB on a CNC machine instead of having it fabricated and shipped; a much cheaper and faster option for those with access to the right tools. A bit more testing had the prototype looking good, but the real proof came when it successfully received GPS signals and spewed valid NMEA messages. The design files are on GitHub but as [Pepijn] says, the project was about the journey more than anything else.

PCMCIA Flash Card Gives Up Its Secrets Thanks To Retro Gear

July 18, 2023 by Dan Maloney 27 Comments

There are two ways to recover data from an obsolete storage medium. One way is to pull out all the tools in the hacker’s kit — with logic analyzers, oscilloscopes, and bit-banged software in a desperate attempt to reverse engineer the original protocol. The other way is to have a really, really deep junk bin that just happens to contain exactly the right pieces that would have been used decades ago.

For recovering data from a 25-year-old PCMCIA memory card, [Dave] from Vintage Apparatus chose the latter method. But to be fair, characterizing the stash of gear he had to select from as a “junk bin” is pretty insulting. It’s more like a museum of retro technology, which just so happened to hold Toshiba Libretto, a subnotebook computer hailing from the late 1990s. The machine sports a pair of PCMCIA slots and was just the thing to read the data from the old 32 MB SanDisk flash card, which once lived in a backpack-mounted GPS system for surveyors.

If this hack sounds as easy as plugging things into an old computer, you’d be right — if you just happen to have a stack of floppies containing the Windows 98 drivers for said things. So [Dave]’s task became a game of finding the right combination of cards that already had the drivers installed and would provide the connectivity needed to get the data off the flash card. Between a suspiciously crunchy-sounding floppy drive and an Ethernet card dongle badly in need of some contact cleaner, cobbling together the right hardware was a bit of a chore. After that, a lot of the hack was [Dave] just remembering how we used to do things back in the day, with the eventual solution being transferring over the files to an FTP server on a Raspberry Pi.

The video below tells the whole saga, but the real treat might just be the Vintage Apparatus collection of gear. Incidentally, we really like [Dave]’s idea for storing associated bits and bobs.

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The Voice Of GPS

June 23, 2023 by Al Williams 7 Comments

Tuning into a GPS satellite is nothing new. Your phone and your car probably do that multiple times a day. But [dereksgc] has been listening to GPS voice traffic. The traffic originates from COSPAS-SARSAT, which is a decades-old international cooperative of 45 nations and agencies that operates a worldwide search and rescue program. You can watch a video about it below.

Nominally, a person in trouble activates a 406 MHz beacon, and any of the 66 satellites that host COSPAS-SARSAT receivers can pick it up and relay information to the appropriate authorities. These beacons are often attached to aircraft or ships, but there are an increasing number of personal beacons used by campers, hikers, and others who might be in danger and out of reach of a cell phone. The first rescue from this system was in 1982. By 2021, 3,632 people were rescued thanks to the system.

The satellites that listen to the beacon frequencies don’t process the signals. They use a transponder that re-transmits anything it hears on a much higher downlink frequency. These transponders are always payloads on other satellites like navigation or weather satellites. But because the transponder doesn’t care what it hears, it sometimes rebroadcasts signals from things other than beacons. We were unclear if these were rogue radios or radios with spurious emissions in the translator’s input range.

The video has practical tips on how to tune in several of the satellites that carry these transponders. Might be a fun weekend project with a software-defined radio.

We’ve seen homebrew satellite devices, but none for an emergency beacon — we aren’t sure what the legal aspects of that would be. There are other satellites that unknowingly host pirate radio stations, too.

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