Radio Hacks

1472 Articles

A web interface is shown providing information about a cellular network base station.

Running Your Own 3G Network

May 9, 2026 by 14 Comments

CDMA2000 was one of the protocols defined for 3G networks and is now years out of date and being phased out worldwide. Nevertheless, there are still vast numbers of phones that will happily connect to it, creating an opportunity for hackers seeking to run their own cellular networks. [Chrismoos] recently made this endeavour significantly easier by releasing 1xBTS, a Rust implementation of the lower three layers of a CDMA2000 network.

The lowest layer of the stack is an SDR for the actual radio communications. It’s been tested with the USRP B200 and B210, the LimeSDR Mini 2, and the BladeRF Micro 2.0. The code might work with certain other SDRs using the SoapySDR abstraction layer. The SDR is controlled by the base station (BTS) software, which, in turn, is controlled by the base station controller (BSC) over an Abis link. The BSC manages channels and mobile device associations, and exchanges frames with the mobile switching center (MSC), which handles message switching.

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This Az-El Mount Is Worth Following

May 7, 2026 by 7 Comments

Communication with satellites often involves the use of high-gain directional antennas coupled with careful positioning to find and track the target. With a geostationary satellite the mount is either fixed or a single-axis polar mount, but when the craft is moving in a different orbit it becomes more of a challenge to stay locked on. An azimuth-elevation mount is needed to cover the whole sky, and [Ham Radio Passion] has one as a work in progress. It’s 3D printed and looks straightforward, making it a project to watch.

An az-el mount has two parts, the first being a turntable to set the azimuth, and the second being a horizontal rotating axis to set the elevation. He’s mounting the antenna to a piece of aluminium extrusion and driving it through a set of 3D printed gears driven from a 360 degree servo with a worm drive. He explains why the servo makes more sense to him here.

The result is not yet a finished project, but it shows enough promise to make it worth keeping an eye on. It’s by no means big enough for a huge antenna array, but we can imagine antennas for higher frequencies would be well within its capabilities. Meanwhile it’s certainly not the first az-el mount we’ve seen.

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A 1947 Radio Gets A Face Lift

May 6, 2026 by 5 Comments

We’ve all done it. We spy an old radio at a garage sale or resale shop. We know someone should bring it back to life, but it looks like a project, so we pass it by. Not [Ken] from [Ken’s Shop]. He found an Arvin 664A AM radio from 1947 in what appears to be a home-built cabinet and decided to bring it back to life.

From what we could find, the original case was a white plastic, not the wood box it is in today. So the first challenge was simply getting inside to see what was going on. Continue reading “A 1947 Radio Gets A Face Lift” →

A red box with a yellow front panel is shown. The front panel contains a power switch, an indicator light, and a small OLED display.

A Shortwave Sensor To Monitor The Ionosphere

May 4, 2026 by 9 Comments

The ionosphere is of great importance to shortwave radio transmissions, since it allows radio waves to be refracted and reflected over the horizon, and it’s therefore unfortunate that the height and thickness of the ionosphere depends on the time of day or night, weather, season, and the solar cycle. To get a better idea of current transmission conditions, [mircemk] built this shortwave propagation monitor.

The monitor provides a basic measure of ionosphere conditions by measuring the strength of received shortwave signals: if the conditions for transmission are good, it should receive a relatively high level of existing signals, and a weak signal if conditions are bad. It has an external antenna connected to a signal strength indicator circuit based on the CA3089, which amplifies signals in the 1-40 MHz range and outputs a smoothed voltage indicating the RF energy in this range. The output signal can be read by any voltmeter, in this case an Arduino Nano with an OLED display. Assuming the same antenna is always used, the signal should noticeably fluctuate between night and day as the solar wind affects the ionosphere.

Of course, the distance at which you’ll be receiving a signal means nothing unless you have a receiver, which can range from the antique to the modern.

Flipper Zero Transmits APRS With No Extra Parts

April 21, 2026 by 9 Comments

APRs is an amateur radio protocol allowing the exchange of short packets of data. It’s commonly used to transmit a GPS position, though it can find other applications. The Flipper Zero RF hacker’s multi tool normally needs to be hooked up to an external transmitter to do APRS, but [Richard YO3GND] has made his Flipper do the job without any external parts at all.

One of the the Flipper’s radios sits in the 435 MHz ISM band, meaning that the rest of the 70 cm amateur band is well within its reach. There only remains the subject of modulation, in which the Flipper’s FSK and APRS’s FM are similar on paper if not on a waterfall display. Some software hackery ensues, and the Flipper is an APRS station. Because of the FSK-as-FM modulation it won’t be decoded by everything, but you can’t argue with the bill of materials if you happen to own a Flipper. Check out the demo video below.

Meanwhile, should any readers with an amateur radio licence be interested, this certainly isn’t the first time we’ve brought you a minimalist APRS transceiver. Assuming that possession of a Flipper hasn’t got you into hot water, that is. Continue reading “Flipper Zero Transmits APRS With No Extra Parts” →

Passive Radar Explained

April 12, 2026 by 31 Comments

It is an old trope in submarine movies. A sonar operator strains to hear things in the ocean but dares not “ping” for fear of giving away the boat’s location. Radar has a similar problem. If you want to find an airplane, for example, you typically send a signal out and wait for it to bounce off the airplane. The downside is that the airplane now knows exactly where your antenna is and, these days, may be carrying missiles to home in on it. In a recent post, [Jehan] explains how radar, like sonar, can be passive.

Even if you aren’t worried about a radar-homing missile taking out your antenna, passive radar has other advantages. You don’t need an expensive transmitter or antenna, a simple SDR can pull it off. You don’t need a license for the frequencies you want to use, either. You are just listening.

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934 MHz: When The Government Really Doesn’t Want You To Have CB

April 7, 2026 by 39 Comments

In the mid 1970s there were a spate of movies depicting the romance and lifestyle of truck drivers in the southern half of the United States. Over on the other side of the Atlantic these were naturally received not as works of drama but as documentaries, and thus began a craze for British drivers to do up their Ford Capri so in the right light and with your eyes nearly closed, it almost looked like Burt Reynolds’ Pontiac Trans Am from Smokey and the Bandit.

Such a fine automobile was of course incomplete without a CB radio, highly illegal at the time, which led to an underground CB craze and its eventual legalization in 1981. [Ringway Manchester] is here with a tale from that era, of 934 MHz CB, an odd and underused allocation that was eventually phased out for commercial services.

When UK CB was eventually legalized by the government, it was very obvious that they really didn’t want to. Brits got 27 MHz as FM only with meager power and a weird set of frequencies that nobody else had, and a second band way up in the UHF range, at 934 MHz. We remember they originally tried to make a UHF band the only allocation on purpose because it was nearly useless for mobile operation, and Brits only got 27 MHz by fighting back in the political lobbying space.

The video below tells the story of the band, with relatively scarce and expensive equipment leading to it being an exclusive band more similar to the amateur bands, with little resemblance to its raucous 27 MHz counterpart. How much activity there was depended very much on where in the country you were, which of course wasn’t where your Hackaday scribe was as a teenager even if it had been affordable. Eventually the government saw the little flashing pound signs and grabbed it back for a mobile radio service that never materialized, and now the frequencies are part of the mobile phone spectrum.

Have a watch for an odd bit of UK radio nostalgia and some 2020s illegal CB’ers, and if you want more it’s a subject we’ve touched on before.

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