Writing A GPS Receiver From Scratch

March 18, 2025 by Bryan Cockfield 21 Comments

GPS is an incredible piece of modern technology. Not only does it allow for locating objects precisely anywhere on the planet, but it also enables the turn-by-turn directions we take for granted these days — all without needing anything more than a radio receiver and some software to decode the signals constantly being sent down from space. [Chris] took that last bit bit as somewhat of a challenge and set off to write a software-defined GPS receiver from the ground up.

As GPS started as a military technology, the level of precision needed for things like turn-by-turn navigation wasn’t always available to civilians. The “coarse” positioning is only capable of accuracy within a few hundred meters so this legacy capability is the first thing that [Chris] tackles here. It is pretty fast, though, with the system able to resolve a location in 24 seconds from cold start and then displaying its information in a browser window. Everything in this build is done in Python as well, meaning that it’s a great starting point for investigating how GPS works and for building other projects from there.

The other thing that makes this project accessible is that the only other hardware needed besides a computer that runs Python is an RTL-SDR dongle. These inexpensive TV dongles ushered in a software-defined radio revolution about a decade ago when it was found that they could receive a wide array of radio signals beyond just TV.

All-Band Receiver Lets You Listen To All The Radio At Once

January 9, 2025 by Dan Maloney 52 Comments

There are many ways to build a radio receiver, but most have a few things in common, such as oscillators, tuned circuits, detectors, mixers, and amplifiers. Put those together in the right order and you’ve got a receiver ready to tune in whatever you want to listen to. But if you don’t really care about tuning and want to hear everything all at once, that greatly simplifies the job and leaves you with something like this homebrew all-band receiver.

Granted, dispensing with everything but a detector and an audio amplifier will seriously limit any receiver’s capabilities. But that wasn’t really a design concern for [Ido Roseman], who was in search of a simple and unobtrusive way to monitor air traffic control conversations while flying. True, there are commercially available radios that tune the aviation bands, and there are plenty of software-defined radio (SDR) options, but air travel authorities and fellow travelers alike may take a dim view of an antenna sticking out of a pocket.

So [Ido] did a little digging and found a dead-simple circuit that can receive signals from the medium-wave bands up into the VHF range without regard for modulation. The basic circuit is a Schottky diode detector between an antenna and a high-gain audio amplifier driving high-impedance headphones; [Ido] built a variation that also has an LM386 amplifier stage to allow the use of regular earbuds, which along with a simple 3D-printed case aids in the receiver’s stealth.

With only a short piece of wire as an antenna, reception is limited to nearby powerful transmitters, but that makes it suitable for getting at least the pilot side of ATC conversations. It works surprisingly well — [Ido] included a few clips that are perfectly understandable, even if the receiver also captured things like cell phones chirping and what sounds like random sferics. It seems like a fun circuit to play with, although with our luck we’d probably not try to take it on a plane.

A New Chinese Radio Breaks Cover, Is It Worth It?

October 26, 2024 by Jenny List 25 Comments

Scanning the firehose of new electronic kits and modules coming from the usual Chinese suppliers can be a rewarding experience, as sometimes among the endless breakout boards comes an item that looks interesting enough to try. As an example there’s a receiver kit being given a quick review by [Tech Minds], offering AM and HF multi-mode, FM broadcast, and air band alongside what appear to be digital streaming features.

Looking at it, though all the RF part is hidden under screening cans we’re guessing it might contain one of the Silicon Labs all-in-one receiver chips, but the whole appears to deliver a useful receiver with a comprehensive interface. The review isn’t quite technical enough so we can’t glean a lot more, but it looks as though it could be useful. We’d be tempted to snag one for review, but since with very few exceptions we pay for the stuff we review, it’s a mite expensive at $50+ for yet another radio.

There’s an ongoing question with all these cheap kits and modules though, first of all where did the design come from and are we freeloading on someone else’s hard work, but then whether or not what you’re getting is a knock-off using defective semiconductors or with bean-counting parts removal degrading performance. We’re guessing more will come out about this radio in due course, and we can all make our own judgement. Meanwhile this one can be found on AliExpress or Banggood, so take a look and see if you’re tempted.

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Stressless Shortwave Reviewed

March 12, 2024 by Al Williams 17 Comments

[Dan Robinson] picked up a shortwave receiver known as the “stressless” receiver kit. We aren’t sure if the stress is from building a more complicated kit or operating a more complicated receiver. Either way, it is an attractive kit that looks easy to build.

Presumably to reduce stress, the VFO and receiver boards are already built, so assembly is just a few hours connecting large components and boards. As kits go, this is a fairly simple one. We were surprised to read that the supplier says you can’t upgrade the firmware. We, of course, wonder if that’s true.

For technical specs, the receiver is AM only and can operate from 100 kHz to 30 MHz. It uses a double conversion with intermediate frequencies of 21.4 MHz and 455 kHz. There’s a BNC connector on the back, and the radio requires 11 to 15V on the input. Apparently, the frequency generator inside is an SI5351. The sensitivity and selectivity numbers look very good for an AM radio.

We were surprised to see the radio didn’t have provisions for SSB since AM-only makes it not as useful for hams or others interested in non-broadcast transmissions. If we are doing our conversions correctly, the kit is fairly pricey, too, especially considering that it is AM only.

Still, we like that you could easily assemble a nice-looking radio kit. We were interested in hearing it perform, and [Dan’s] video lets us virtually try it out without the effort. We’ve seen the SI5351 on a carrier if you want to roll your own. Come to think of it, we’ve seen several.

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Building A GPS Receiver From The Ground Up

January 2, 2024 by Bryan Cockfield 15 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.

DIy Arduino FM radio enclosure with the lid off, showing the electronics inside

DIY Arduino Due TEA5767 FM Radio

October 8, 2022 by Dave Walker 10 Comments

Older hackers will remember that a crystal set radio receiver was often one of the first projects attempted. Times have changed, but there’s still something magical about gathering invisible signals from the air and listening to the radio on a homemade receiver. [mircemk] has brought the idea right up to date by building an FM radio with an OLED display, controlled with a rotary encoder.

The design is fairly straightforward, based as it is on another project that [mircemk] found on another site, but the build looks very slick and would take pride of place on any hacker’s workbench. An Arduino Due forms the heart of the project, controlling a TEA5767 module, an SH1106 128×64 pixel OLED display and a rotary encoder. The sound signal is passed through an LM4811 headphone amplifier for private listening, and a PAM8403 Class D audio amplifier for the built-in loudspeaker. The enclosure is made from PVC panels, and accented with colored adhesive tape for style.

It’s easier than ever before to quickly put together projects like this by connecting pre-built modules and downloading code from the Internet, but that doesn’t mean it’s not a worthwhile way to improve your skills and make some useful devices like this one. There are so many resources available to us these days and standing on the shoulders of giants has always been a great way to see farther.

We’ve shown some other radio projects using Arduinos and the TEA5767 IC in the past, such as this one on a tidy custom PCB, and this one built into an old radio case.

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Shortwave Radio Picks Up Sideband

September 29, 2021 by Al Williams 14 Comments

With the push to having most of a radio receiver as part of a PC, it might seem odd to have a standalone communication receiver, but [OM0ET] reviews the latest one he picked up, an ATS25. Inside isn’t much: a battery, a speaker, an encoder, and a Si4732 that provides the RF muscle.

It appears the receiver is pretty broadband which could be a problem. [OM0ET] suggests adding selectivity in the antenna or adding an extra board to use as a bandpass filter.

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