Radio Hacks

1501 Articles

A laptop is shown set up on a desk next to a spectrum analyser, an SDR, and two antennas. The antennas are aimed toward assorted electronics, including headphones and a phone handset.

Reviving TEMPEST Attacks With An Injected Signal

September 20, 2026 by 2 Comments

TEMPEST attacks are often the most effective way to break air-gapped security: rather than directly accessing a computer, the attacker records the system’s unintended radio emissions and uses them to reconstruct its internal operations. This kind of attack was much more effective in the days of noisy, high-voltage CRT displays, and has gradually become less effective as electronics migrate to quieter, less powerful components. A group of researchers, however, has found that even modern electronics can become effective TEMPEST transmitters when irradiated with an RF signal.

The RF a device emits depends on the unintentional antennas in its internal structure. These are difficult to eliminate, and it’s usually not worth the effort; they’re usually small enough that they only effectively radiate at much higher frequencies than the electronics carry. The researchers’ technique, called InjectEave, radiated these electronics with a radio frequency tuned to their internal antennas, injecting that frequency into the circuit. Nonlinear electronic components, such as amplifiers, then mix the injected frequency with the internal signal, creating RF sidebands. This mixed signal then radiates out of the device and can be picked up and demodulated to recover the device’s internal signal.

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A Bandpass Filter Pulls In The Signals

September 20, 2026 by 8 Comments

It’s an unfortunate side effect of proximity to a large transmitter that the received signal can overload a receiver’s front end even when tuned to other frequencies. [Rfrht]’s had this problem with nearby FM broadcast transmissions overloading the 2 metre and 70 centimetre amateur bands. The solution?  Design and build a bandpass filter. This allows the signals you want to pass through while rejecting or attenuating out-of-band frequencies. The resulting PCB is very nice indeed.

On board, aside from the filters themselves, are a low-noise preamplifier and relays to switch between receive and transmit. Everything is controlled by logic-level signals. All components are surface-mount, and the PCB layout clearly takes special care with RF routing.

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TV Audio Tube Makes A Transceiver

September 18, 2026 by 13 Comments

It’s not often we see a tube project here, so [Helge Fykse]’s PCL86 transceiver is a welcome find.

If you know anything about the European Pro-Electron device naming system you’ll be familiar with it as it applies to tubes. The first letter denotes the heater specification, for example “E” is for a 6.3 volt heater. Everyone wants the familiar 6.3 V devices, but they have a set of cousins which often pass unnoticed. “P” tubes have a 300 mA heater designed such that all tubes in a device could be connected in series at the same current. Of those tubes the PCL86 is a mundane example, filling the function taken in the semiconductor years by the LM386. It’s a small-signal triode and a power pentode in one device, and it’s an audio amplifier. Every 1960s TV set in Europe had one, and thus it’s a good choice for experimentation.

This transceiver is a conventional crystal oscillator and power amplifier on transmit, but with a flick of a switch it transforms into a direct conversion receiver in which the triode becomes oscillator and mixer while the pentode becomes an audio amplifier. It’s simple, and the video below the break explains it in great detail. We’re not sure whether or not it could unintentionally radiate in receive mode, but we’re guessing the energy would be tiny.

A simple tube project can make an interesting departure from modern surface mount electronics, so if you get the chance we’d suggest you try one. If you don’t need a transceiver, an audio amplifier is the archetypal PCL86 project.

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FCC ISM Rules May Shatter Lora Mesh Communities

September 17, 2026 by 114 Comments

Although everyone has their own reasons for exploring a new hobby, one of the driving factors behind the popularity of Meshtastic and MeshCore has been the incredible accessibility offered by off-grid LoRa mesh networks. You don’t need any expensive hardware or a license to get on the air — armed with a $20 microcontroller dev board and open source software, you could be on the mesh in minutes. Then came the really exciting part, seeing who else was out there. The low barrier of entry and ad-hoc nature of these projects meant there was a good chance you’d soon find yourself exchanging messages with other like-minded folks in the area.

Or at least, that’s how it used to be. With the recent revelation that their default radio configurations have potentially been in violation of the Federal Communications Commission’s (FCC) regulations governing amateur usage of the 900 MHz industrial, scientific and medical (ISM) band, the users and developers of both Meshtastic and MeshCore have been sent scrambling. Getting in compliance isn’t necessarily a technical challenge. In fact, Meshtastic has already introduced changes aimed to address the issue and anyone running the latest alpha release can be sure that their initial radio configuration will meet FCC standards.

But unfortunately, this introduces a new problem. While it’s easy enough to get new installations of Meshtastic and MeshCore operating in a mode that keeps the FCC happy, doing so breaks compatibility with everything that’s already been deployed. The community will be fractured into distinct strata depending on when they first configured their hardware, with an added dash of confusion from the more rebellious users who will undoubtedly refuse to migrate over to the new settings.

What was once easy and accessible has just gotten a whole lot more complicated.

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It’s GNU Radio Companion, But In The Browser

September 9, 2026 by 15 Comments

The progression of the web browser from a tool for simple static information browsing into a do-everything computing environment has been inexorable, with package after package making the jump. Today it’s the turn of GNU Radio Companion, lowering the barrier to software defined radio considerably. It’s the work of [Marc Lichtman], who’s name you may recall if you have ever used pysdr.org.

Loading it up gives you a very familiar window if you’re used to GNU Radio Companion, and it comes with a set of example flowgraphs that cover a large range of applications. It supports a collection of software-defined radios (SDRs) including the well-known RTL-SDR, and if that’s not enough it can also use your sound card. There is even a set of recorded off-air captures to experiment with.

We’ve spent a while here playing with it, and it does everything we’re used to from the version outside the browser. The only thing we’re told it won’t do is work with a networked SDR, but that’s no deal breaker.

Thanks [Marcus Müller] for the tip.

A Thoroughly Modern Minimalist Transceiver

September 3, 2026 by 9 Comments

Making a radio is so often a case of taking tried and tested designs and working with them to create something new. It’s a safe way to make something that works. [Riyas] however has gone for an entirely different tack, creating an entirely modern transceiver with as much as possible going on in the silicon.

At its heart are three integrated circuits, the familiar Si5351 as a transmit VFO, an Si4372 receiver, and an RP2040 tying it all together. This microcontroller functions both as controller, and as an ADC to provide a software defined radio via its USB port. The Si4372 having an internal SDR architecture and its output being digitized again is not lost on us.

It’s for digital modes and CW only, but we’d venture the opinion that those are where the interesting stuff is anyway. We certainly like it for its simplicity, and also for the one-cable solution it offers. So many other designs need a sound card and extra cables, this one makes for a lot less clutter. We hope we’ll see more development on this design over time, it could become a favorite in the homebrew rig stakes.

Meanwhile the Si5351 is notoriously annoying to program. A while back we covered a library that might help, if you get stuck.

It’s Teletext, But On The Radio

September 1, 2026 by 18 Comments

Old-school teletext with its pixelated text and block graphics may now be largely a thing of the past, but that doesn’t mean it’s without enthusiasts or there’s no more life in the idea. [M7TJF] has a project which takes teletext and puts it on amateur radio through the magic of AX.25. It’s called CEEFAX Station, in honor of the BBC’s teletext offering from back in the day.

What you get is a Linux package or a Windows executable, which you run and presumably hook the computer up to a radio. It can either be a transmitting node or a receiving one for browsing pages, and there’s an online map to track who’s doing either and on what frequencies. This is all brand new so there’s not much on there at the moment, but we expect that as people try this mode, this will change.

Sadly it’s a little unclear on how the protocol works and how the pages are encoded, but it’s early days. Meanwhile if you hanker for the real thing, it’s still about in some places.