Radio Hacks

1434 Articles

Radio Repeaters In The Sky

April 30, 2025 by 10 Comments

One of the first things that an amateur radio operator is likely to do once receiving their license is grab a dual-band handheld and try to make contacts with a local repeater. After the initial contacts, though, many hams move on to more technically challenging aspects of the hobby. One of those being activating space-based repeaters instead of their terrestrial counterparts. [saveitforparts] takes a look at some more esoteric uses of these radio systems in his latest video.

There are plenty of satellite repeaters flying around the world that are actually legal for hams to use, with most being in low-Earth orbit and making quick passes at predictable times. But there are others, generally operated by the world’s militaries, that are in higher geostationary orbits which allows them to serve a specific area continually. With a specialized three-dimensional Yagi-Uda antenna on loan, [saveitforparts] listens in on some of these signals. Some of it is presumably encrypted military activity, but there’s also some pirate radio and state propaganda stations.

There are a few other types of radio repeaters operating out in space as well, and not all of them are in geostationary orbit. Turning the antenna to the north, [saveitforparts] finds a few Russian satellites in an orbit specifically designed to provide polar regions with a similar radio service. These sometimes will overlap with terrestrial radio like TV or air traffic control and happily repeat them at brief intervals.

[saveitforparts] has plenty of videos looking at other satellite communications, including grabbing images from Russian weather satellites, using leftover junk to grab weather data from geostationary orbit, and accessing the Internet via satellite with 80s-era technology.

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Open Source DMR Radio

April 19, 2025 by 4 Comments

While ham radio operators have been embracing digital mobile radio (DMR), the equipment is most often bought since — at least in early incarnations — it needs a proprietary CODEC to convert speech to digital and vice versa. But [QRadioLink] decided to tackle a homebrew and open source DMR modem.

The setup uses a LimeSDR, GNU Radio, and Codec2. There are some other open DMR projects, such as OpenRTX. So we are hopeful there are going to be more choices. The DMR modem, however, is only a proof-of-concept and reuses the MMDVMHost code to do the data link layer.

[QRadioLink] found several receiver implementations available, but only one other DMR transmitter — actually, a transceiver. Rather than use an AMBE hardware device or the potentially encumbered mbelib codec, the project uses Codec2 which is entirely open source.

There’s a lot of explanation about the data collection to prepare for the project, and then a deep dive into the nuts and bolts of the implementation. You might enjoy the video below to see things in action.

If you just want to listen to DMR, it’s easy. If Codec2 sounds familiar, it is part of M17.

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Brush Up On Your Trade Craft With This Tiny FM Bug

April 11, 2025 by 19 Comments

Would-be spooks and spies, take note: this one-transistor FM transmitter is a circuit you might want to keep in mind for your bugging needs. True, field agents aren’t likely to need to build their own equipment, but how cool a spy would you be if you could?

Luckily, you won’t need too many parts to recreate [Ciprian (YO6DXE)]’s project, most of which could be found in a decently stocked junk bin, or even harvested from e-waste. On the downside, the circuit is pretty fussy, with even minor component value changes causing a major change in center frequency. [Ciprian] had to do a lot of fiddling to get the frequency in the FM band, particularly with the inductor in the LC tank circuit. Even dropping battery voltage shifted the frequency significantly, which required a zener diode to address.

[Ciprian] ran a few tests and managed to get solid copy out to 80 meters range, which is pretty impressive for such a limited circuit. The harmonics, which extend up into the ham bands and possibly beyond, are a bit of a problem; while those could be addressed with a low-pass filter, in practical terms, the power of this little fellow is probably low enough to keep you from getting into serious trouble. Still, it’s best not to push your luck.

While you’re trying your hand at one-transistor circuits, you might want to try [Ciprian]’s one-transistor CW transceiver next.

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Farewell Economy 7, A Casualty Of The Long Wave Switch-Off

April 10, 2025 by 36 Comments

If you paid attention to advertising in 1980s Britain, you were never far from Economy 7. It was the magic way to heat your house for less, using storage heaters which would run at night using cheap electricity, and deliver warmth day-long. Behind it all was an unseen force, a nationwide radio switching signal transmitted using the BBC’s 198 kHz Long Wave service. Now in 2025 the BBC Radio 4 Long Wave service it relies on is to be turned off, rendering thousands of off-peak electricity meters still installed, useless. [Ringway Manchester] is here to tell the tale.

The system was rolled out in the early 1980s, and comprised of a receiver box which sat alongside your regular electricity meter and switched in or out your off-peak circuit. The control signal was phase-modulated onto the carrier, and could convey a series of different energy use programs. 198 kHz had the useful property due to its low frequency of universal coverage, making it the ideal choice. As we’ve reported in the past the main transmitter at Droitwich is to be retired due to unavailability of the high-power vacuum tubes it relies on, so now time’s up for Economy 7 too. The electricity companies are slow on the uptake despite years of warning, so there’s an unseemly rush to replace those old meters with new smart meters. The video is below the break.

The earliest of broadcast bands may be on the way out, but it’s not entirely over. There might even be a new station on the dial for some people.

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Lockdown Remote Control Project Is Free And Open

April 4, 2025 by 8 Comments

If you flew or drove anything remote controlled until the last few years, chances are very good that you’d be using some faceless corporation’s equipment and radio protocols. But recently, open-source options have taken over the market, at least among the enthusiast core who are into squeezing every last bit of performance out of their gear. So why not take it one step further and roll your own complete system?

Apparently, that’s what [Malcolm Messiter] was thinking when, during the COVID lockdowns, he started his own RC project that he’s calling LockDownRadioControl. The result covers the entire stack, from the protocol to the transmitter and receiver hardware, even to the software that runs it all. The 3D-printed remote sports a Teensy 4.1 and off-the-shelf radio modules on the inside, and premium FrSky hardware on the outside. He’s even got an extensive folder of sound effects that the controller can play to alert you. It’s very complete. Heck, the transmitter even has a game of Pong implemented so that you can keep yourself amused when it’s too rainy to go flying.

Of course, as we alluded to in the beginning, there is a healthy commercial infrastructure and community around other open-source RC projects, namely ExpressLRS and OpenTX, and you can buy gear that runs those software straight out of the box, but it never hurts to have alternatives. And nothing is easier to customize and start hacking on than something you built yourself, so maybe [Malcolm]’s full-stack RC solution is right for you? Either way, it’s certainly impressive for a lockdown project, and evidence of time well spent.

Thanks [Malcolm] for sending that one in!

Dwingeloo telescope with sun shining through

Dwingeloo To Venus: Report Of A Successful Bounce

March 28, 2025 by 14 Comments

Radio waves travel fast, and they can bounce, too. If you are able to operate a 25-meter dish, a transmitter, a solid software-defined radio, and an atomic clock, the answer is: yes, they can go all the way to Venus and back. On March 22, 2025, the Dwingeloo telescope in the Netherlands successfully pulled off an Earth-Venus-Earth (EVE) bounce, making them the second group of amateurs ever to do so. The full breakdown of this feat is available in their write-up here.

Bouncing signals off planets isn’t new. NASA has been at it since the 1960s – but amateur radio astronomers have far fewer toys to play with. Before Dwingeloo’s success, AMSAT-DL achieved the only known amateur EVE bounce back in 2009. This time, the Dwingeloo team transmitted a 278-second tone at 1299.5 MHz, with the round trip to Venus taking about 280 seconds. Stockert’s radio telescope in Germany also picked up the returning echo, stronger than Dwingeloo’s own, due to its more sensitive receiving setup.

Post-processing wasn’t easy either. Doppler shift corrections had to be applied, and the received signal was split into 1 Hz frequency bins. The resulting detections clocked in at 5.4 sigma for Dwingeloo alone, 8.5 sigma for Stockert’s recording, and 9.2 sigma when combining both datasets. A clear signal, loud and proud, straight from Venus’ surface.

The experiment was cut short when Dwingeloo’s transmitter started failing after four successful bounces. More complex signal modulations will have to wait for the next Venus conjunction in October 2026. Until then, you can read our previously published article on achievements of the Dwingeloo telescope.

RTL-SDR With Only A Browser

March 23, 2025 by 16 Comments

Surely by now you’ve at least heard of RTL-SDR — a software project that let’s cheap TV tuner dongles work as a software-defined radios. A number of projects and tools have spun off the original effort, but in his latest video, [Tech Minds] shows off a particularly unique take. It’s a Web browser-based radio application that uses WebUSB, so it doesn’t require the installation of any application software. You can see the program operating in the video below.

There are a few things you should know. First, you need the correct USB drivers for your RTL-SDR. Second, your browser must support WebUSB, of course. Practically, that means you need a Chromium-type browser. You may have to configure your system to allow raw access to the USB port, too.

Watching the video, you can see that it works quite well. According to the comments, it will work with a phone, too, which is an interesting idea. The actual Web application is available as open source. It isn’t going to compete with a full-fledged SDR program, but it looked surprisingly complete.

These devices have grown from a curiosity to a major part of radio hacking over the years. Firefox users can’t use WebUSB — well, not directly, anyway.

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