Radio Hacks

1430 Articles

Hard Hat Becomes Bluetooth Direction Finder

September 30, 2025 by 10 Comments

Have you ever wanted to find a Bluetooth device out in the wild while looking like the comic relief character from a science-fiction series? You might like Dendrite, the direction-finding hat from [SolidStat3].

Dendrite is intended for hunting down Bluetooth devices. It’s capable of direction estimation based on signal strength readings from four ESP32 microcontrollers mounted on an off-the-shelf hard hat. Each ESP32 searches for BLE devices in the immediate area and reports the apparent signal strength to a fifth ESP32, which collates readings from all units. It then runs a simple multilateration algorithm to estimate the direction of the device. This information is then displayed via a ring of addressable LEDs around the perimeter of the hat. White LEDs marking the direction of the detected device. The only problem? You can’t see the LEDs while you’re wearing the hat. You might need a friend to help you… or you can simply take it off to see what it’s doing.

Ultimately, this project is a useful direction-finding hard hat that would also make a perfect prop from an episode of Inspector Spacetime. We’ve covered direction finding in other contexts before, too. Meanwhile, if you’re cooking up your own innovative hard hat (or radio) hacks, don’t hesitate to let us know!

A Ham-Adjacent Portable Radio Repeater

September 26, 2025 by 45 Comments

Although ham radio offers a wide array of bands to transmit on, not to mention plenty of modes to communicate with, not everyone wants or needs to use all of this capability. For those needing simple two-way communication services like FRS or GMRS are available (in North America) with much less stringent licensing requirements, and GMRS even allows repeaters to be used to extend their range beyond the typical mile or so. [Dave] aka [N8DAV] has built an off-grid simplex repeater that can travel around with him wherever he goes.

The repeater itself is based on a pre-built simplex repeater module, which means that it has to record an incoming signal and then play it back on the same frequency. Compared to a split frequency repeater which uses different frequencies for transmit and receive this can be a bit cumbersome but simplifies the design and the use. A Baofeng UV-5R is used to perform the actual radio duties paired to a 40 watt amplifier to extend the range as much as possible. It’s all packed into a Pelican-like case and set up with a large battery that could power it for a number of days, making it useful for camping, rescue, or other off-grid activities.

For those wondering why [Dave] is using his ham call sign instead of his GMRS one, all of the equipment in this build will work in either the UHF ham bands or the channels reserved for GMRS with minor adjustments, so it’s perfectly possible to use the setup for one’s preferred license. And, for those in other parts of the world without GMRS there’s a similar class of radio called UHF CB which might be able to support similar builds, but be sure to check your local jurisdiction’s laws before hooking something like this up. For an even longer-range radio repeater using similar equipment we’d recommend looking to the skies.

Continue reading “A Ham-Adjacent Portable Radio Repeater” →

Building Your Own DVB-S2 Receiver

September 22, 2025 by 9 Comments

Generally, a digital TV tuner is something you buy rather than something you make yourself. However, [Johann] has always been quite passionate about the various DVB transmission standards, and decided he wanted to build his own receiver just for the fun of it.

[Johann]’s build is designed to tune in DVB-S2 signals transmitted from satellites, and deliver that video content over a USB connection. When beginning his build, he noted it was difficult to find DVB reception modules for sale as off-the-shelf commercial parts. With little to nothing publicly available, he instead purchased a “Formuler F1 Plug & Play DVB-S2 HDTV Sat Tuner” and gutted it for the Cosy TS2M08-HFF11 network interface module (NIM) inside. He then paired this with a Cypress CY7C68013A USB bridge to get the data out to a PC. [Johann] then whipped up a Linux kernel driver to work with the device.

[Johann] doesn’t have hardcore data on how his receiver performs, but he reports that it “works for me.” He uses it in South Germany to tune in the Astra 19.2E signal.

We don’t talk a lot about DVB these days, since so much video content now comes to us over the Internet. However, we have still featured some nifty DVB hacks in the past. If you’re out there tinkering with your own terrestrial or satellite TV hardware, don’t hesitate to notify the tipsline!

The Inside Story Of The UK’s Great CB Petrol Scam

September 19, 2025 by 28 Comments

Looking at gasoline prices today, it’s hard to believe that there was a time when 75 cents a gallon seemed outrageous. But that’s the way it was in the 70s, and when it tripped over a dollar, things got pretty dicey. Fuel theft was rampant, both from car fuel tanks — remember lockable gas caps? — and even from gas stations, where drive-offs became common, and unscrupulous employees found ways to trick the system into dispensing free gas.

But one method of fuel theft that escaped our attention was the use of CB radios to spoof petrol pumps, which [Ringway Manchester] details in his new video. The scam happened in the early 80s, only a few years after CB became legal in the UK but quite a while since illegal use had exploded. The trick involved a CB transceiver equipped with a so-called “burner,” a high-power and highly illegal linear amplifier used to boost the radiated power of the signal. When keyed up in the vicinity of dispensers with digital controls, the dispensing rate on the display would appear to slow down markedly, while the pump itself stayed at the same speed. The result was more fuel dispensed than the amount reported to the cashier.

If this sounds apocryphal, [Ringway] assures us that it wasn’t. When the spoofing was reported, authorities up to and including Scotland Yard investigated and found that it was indeed plausible. The problem appeared to be the powerful RF signal interfering with the pulses from the flowmeter on the dispenser. The UK had both 27 MHz and 934 MHz CB at the time; [Ringway] isn’t clear which CB band was used for the exploit, but we’d guess it was the former, in which case we can see how the signals would interfere. Another thing to keep in mind is that CB radios in the UK were FM, as opposed to AM and SSB in the United States. So we wonder if the same trick would have worked here.

At the end of the day, no matter how clever you are about it, theft is theft, and things probably aren’t going to go well for you if you try to pull this off today. Besides, it’s not likely that pumps haven’t been hardened against these sorts of attacks. Still, if you want a look inside a modern pump to see if you can find any weaknesses, have at it. Just don’t tell them where you heard about it.

Continue reading “The Inside Story Of The UK’s Great CB Petrol Scam” →

Radio Apocalypse: Clearing The Air With SCATANA

September 18, 2025 by 7 Comments

For the most part, the Radio Apocalypse series has focused on the radio systems developed during the early days of the atomic age to ensure that Armageddon would be as orderly an affair as possible. From systems that provided backup methods to ensure that launch orders would reach the bombers and missiles, to providing hardened communications systems to allow survivors to coordinate relief and start rebuilding civilization from the ashes, a lot of effort went into getting messages sent.

Strangely, though, the architects of the end of the world put just as much thought into making sure messages didn’t get sent. The electronic village of mid-century America was abuzz with signals, any of which could be abused by enemy forces. CONELRAD, which aimed to prevent enemy bombers from using civilian broadcast signals as navigation aids, is a perfect example of this. But the growth of civil aviation through the period presented a unique challenge, particularly with the radio navigation system built specifically to make air travel as safe and reliable as possible.

Balancing the needs of civil aviation against the possibility that the very infrastructure making it possible could be used as a weapon against the U.S. homeland is the purpose of a plan called Security Control of Air Traffic and Air Navigation Aids, or SCATANA. It’s a plan that cuts across jurisdictions, bringing military, aviation, and communications authorities into the loop for decisions regarding when and how to shut down the entire air traffic system, to sort friend from foe, to give the military room to work, and, perhaps most importantly, to keep enemy aircraft as blind as possible. Continue reading “Radio Apocalypse: Clearing The Air With SCATANA” →

Getting The Most Out Of ISM Transceivers Using Math

September 17, 2025 by 7 Comments

WiFi is an excellent protocol, but it certainly has its weaknesses. Its range in even a normal home is relatively limited, so you could imagine the sort of performance you’d expect through the hundred meters of dense woodland that [DO3RB] is trying to penetrate. So naturally the solution was to develop a new wireless transceiver for the ISM band. 

Of course, getting reliable packet transmission is tough. In a building with brick walls, WiFi will get around five to ten percent packet loss. For TCP to remain reliable, one percent packet loss is the maximum designed loss of this wireless protocol. In reality, the transceiver achieves 0.075% packet loss real world.

The crux of the magic behind this excellent reliability is the extended binary Golay code. By halving the bitrate, the Golay code is able to correct for up to four errors per codeword. While a more complicated scheme could have been used, the Golay code allowed for easy porting to an MCU thus simplifying the project. All this is encoded with frequency shift keying in the ISM band.

This magic is tied up inside an tiny SAMD21 paired with a RFM12BP wireless front end. Using TinyUSB, the interface shows up to the host as a USB Ethernet adapter making for seamless networking setups. With reliable bi-directional communication, you could theoretically use this as a home networking solution. However, this is realistically best for IoT devices as the speeds are around 56 kbit/s.

While this is an incredibly simple system, harking back to 90s networking, it certainly gets the job done in a neat and tidy manner. And if you too wish hark back to 90s radio communications, make sure to check out this satellite imagery hack next! 

Thanks [Bernerd] for the tip!

It’s A Variable Capacitor, But Not As We Know It

September 17, 2025 by 22 Comments

Radio experimenters often need a variable capacitor to tune their circuits, as the saying goes, for maximum smoke. In decades past these were readily available from almost any scrap radio, but the varicap diode and then the PLL have removed the need for them in consumer electronics. There have been various attempts at building variable capacitors, and here’s [radiofun232] with a novel approach.

A traditional tuning capacitor has a set of meshed semicircular plates that have more of their surface facing each other depending on how far their shaft is turned. The capacitor presented in the first video below has two plates joined by a hinge in a similar manner to the covers of a book. It’s made of tinplate, and the plates can be opened or closed by means of a screw.

The result is a capacitor with a range from 50 to 150 picofarads, and in the second video we can see it used with a simple transistor oscillator to make a variable frequency oscillator. This can form the basis of a simple direct conversion receiver.

We like this device, it’s simple and a bit rough and ready, but it’s a very effective. If you’d like to see another unusual take on a variable capacitor, take a look at this one using drinks cans.

Continue reading “It’s A Variable Capacitor, But Not As We Know It” →