software-defined radio

128 Articles

6502 Puts On An SDR Hat

September 11, 2025 by 11 Comments

The legendary 6502 microprocessor recently turned 50 years old, and to celebrate this venerable chip which brought affordable computing and video gaming to the masses [AndersBNielsen] decided to put one to work doing something well outside its comfort zone. Called the PhaseLoom, this project uses a few other components to bring the world of software-defined radio (SDR) to this antique platform.

The PhaseLoom is built around an Si5351 clock generator chip, which is configurable over I2C. This chip is what creates the phase-locked loop (PLL) for the radio. The rest of the components, including antenna connectors and various filters, are in an Arduino-compatible form factor that let it work as a shield or hat for the 65uino platform, an Arduino-form-factor 6502 board. The current version [Anders] has been working on is dialed in to the 40-meter ham band, with some buttons on the PCB that allow the user to tune around within that band. He reports that it’s a little bit rough around the edges and somewhat noisy, but the fact that the 6502 is working as an SDR at all is impressive on its own.

For those looking to build their own, all of the schematics and code are available on the project’s GitHub page. [Anders] has some future improvements in the pipe for this project as well, noting that with slightly better filters and improved software even more SDR goodness can be squeezed out of this microprocessor. If you’re looking to experiment with SDR using something a little bit more modern, though, this 10-band multi-mode SDR based on the Teensy microcontroller gets a lot done without breaking the bank.

 

 

Roll Your Own SSB Receiver

August 19, 2025 by 3 Comments

[Paul Maine] was experimenting with GNU Radio and an RTL-SDR dongle. He created an SSB receiver and, lucky for us, he documented it all in a video you can see below. He walks through how to generate SSB, too. If videos aren’t your thing, you can go back to the blog post from [Gary Schafer] that inspired him to make the video, which is also a wealth of information.

There is a little math — you almost can’t avoid it when talking about this topic. But [Paul] does a good job of explaining it all as painlessly as possible. The intuitive part is simple: An AM signal has most of its power in the carrier and half of what’s left in a redundant sideband. So if you can strip all those parts out and amplify just one sideband, you get better performance.

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Real-Time Beamforming With Software-Defined Radio

August 5, 2025 by 13 Comments

It is perhaps humanity’s most defining trait that we are always striving to build things better, stronger, faster, or bigger than that which came before. Taller skyscrapers, longer bridges, and computers with more processors, all advance thanks to this relentless persistence.

In the world of radio, we might assume that a better signal simply means adding more power, but performance can also improve by adding more antennas. Not only do more antennas increase gain but they can also be electronically steered, and [MAKA] demonstrates how to do this with a software-defined radio (SDR) phased array.

The project comes to us in two parts. In the first part, two ADALM-Pluto SDR modules are used, with one set to transmit and the other to receive. The transmitting SDR has two channels, one of which has the phase angle of the transmitted radio wave fixed while the other is swept from -180° to 180°. These two waves will interfere with each other at various points along this sweep, with one providing much higher gain to the receiver. This information is all provided to the user via a GUI.

The second part works a bit like the first, but in reverse. By using the two antennas as receivers instead of transmitters, the phased array can calculate the precise angle of arrival of a particular radio wave, allowing the user to pinpoint the direction it is being transmitted from. These principles form the basis of things like phased array radar, and if you’d like more visual representations of how these systems work take a look at this post from a few years ago.

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Writing A GPS Receiver From Scratch

March 18, 2025 by 22 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.

Taylorator Makes Mischief On The Airwaves

January 29, 2025 by 33 Comments

[Stephen] recently wrote in to share his experiments with using the LimeSDR mini to conduct a bit of piracy on the airwaves, and though we can’t immediately think of a legitimate application for spamming the full FM broadcast band simultaneously, we can’t help but be fascinated by the technique. Called the Taylorator, as it was originally intended to carpet bomb the dial with the collected works of Taylor Swift on every channel, the code makes for some interesting reading if you’re interested in the transmission-side of software defined radio (SDR).

The write-up talks about the logistics of FM modulation, and how quickly the computational demands stack up when you’re trying to push out 100 different audio streams at once. It takes a desktop-class CPU to pull it off in real-time, and eats up nearly 4 GB of RAM.

You could use this project to play a different episode of the Hackaday Podcast on every FM channel at once, but we wouldn’t recommend it. As [Stephen] touches on at the end of the post, this is almost certainly illegal no matter where you happen to live. That said, if you keep the power low enough so as not to broadcast anything beyond your home lab, it’s unlikely anyone will ever find out.

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Use Your RTL, In The Browser

December 13, 2024 by 14 Comments

The web browser started life as a relatively simple hypertext reading application, but over the 30+ years since the first one displayed a simple CERN web page it has been extended to become the universal platform. It’s now powerful enough to run demanding applications, for example a full software-defined radio. [Jtarrio] proves this, with an application to use an RTL-SDR, in HTML5.

It’s a fork of a previous Google-Chrome-only FM receiver, using the HTML5 WebUSB API, and converted to TypeScript. You can try it out for yourself if you have a handy RTL dongle lying around, it provides an interface similar to the RTL apps you may be used to.

The Realtek digital TV chipset has been used as an SDR for well over a decade now, so we’re guessing most of you with an interest in radio will have one somewhere. The cheap ones are noisy and full of spurious peaks, but even so, they’re a bucket of fun. Now all that’s needed is the transmit equivalent using a cheap VGA adapter, and the whole radio equation could move into the browser.

Supercon 2023: Receiving Microwave Signals From Deep-Space Probes

October 10, 2024 by 5 Comments

Here’s the thing about radio signals. There is wild and interesting stuff just getting beamed around all over the place. Phrased another way, there are beautiful signals everywhere for those with ears to listen. We go about our lives oblivious to most of them, but some dedicate their time to teasing out and capturing these transmissions.

David Prutchi is one such person. He’s a ham radio enthusiast that dabbles in receiving microwave signals sent from probes in deep space. What’s even better is that he came down to Supercon 2023 to tell us all about how it’s done!

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