Wireless Hacks

1097 Articles

The Android Bluetooth Connection

August 27, 2025 by 14 Comments

Suppose someone came to talk to you and said, “I need your help. I have a Raspberry Pi-based robot and I want to develop a custom Android app to control it.” If you are like me, you’ll think about having to get the Android developer tools updated, and you’ll wonder if you remember exactly how to sign a manifest. Not an appealing thought. Sure, you can buy things off the shelf that make it easier, but then it isn’t custom, and you have to accept how it works. But it turns out that for simple things, you can use an old Google Labs project that is, surprisingly, still active and works well: MIT’s App Inventor — which, unfortunately, should have the acronym AI, but I’ll just call it Inventor to avoid confusion.

What’s Inventor? It lives in your browser. You lay out a fake phone screen using drag and drop, much like you’d use QT Designer or Visual Basic. You can switch views and attach actions using a block language sort of like Scratch. You can debug in an emulator or on your live phone wirelessly. Then, when you are ready, you can drop an APK file ready for people to download. Do you prefer an iPhone? There’s some support for it, although that’s not as mature. In particular, it appears that you can’t easily share an iPhone app with others.

Is it perfect? No, there are some quirks. But it works well and, with a little patience, can make amazingly good apps. Are they as efficient as some handcrafted masterpiece? Probably not. Does it matter? Probably not. I think it gets a bad rep because of the colorful blocks. Surely it’s made for kids. Well, honestly, it is. But it does a fine job, and just like TinkerCad or Lego, it is simple enough for kids, but you can use it to do some pretty amazing things.

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Radio Apocalypse: America’s Doomsday Rocket Radios

August 25, 2025 by 17 Comments

Even in the early days of the Cold War, it quickly became apparent that simply having hundreds or even thousands of nuclear weapons would never be a sufficient deterrent to atomic attack. For nuclear weapons to be anything other than expensive ornaments, they have to be part of an engineered system that guarantees that they’ll work when they’re called upon to do so, and only then. And more importantly, your adversaries need to know that you’ve made every effort to make sure they go boom, and that they can’t interfere with that process.

In practical terms, nuclear deterrence is all about redundancy. There can be no single point of failure anywhere along the nuclear chain of command, and every system has to have a backup with multiple backups. That’s true inside every component of the system, from the warheads that form the sharp point of the spear to the systems that control and command those weapons, and especially in the systems that relay the orders that will send the missiles and bombers on their way.

When the fateful decision to push the button is made, Cold War planners had to ensure that the message got through. Even though they had a continent-wide system of radios and telephone lines that stitched together every missile launch facility and bomber base at their disposal, planners knew how fragile all that infrastructure could be, especially during a nuclear exchange. When the message absolutely, positively has to get through, you need a way to get above all that destruction, and so they came up with the Emergency Rocket Communication System, or ERCS.

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Quieting That Radio

August 22, 2025 by 22 Comments

If you are casually listening to the radio, you probably tune into a local station and with modern receivers and FM modulation, the sound quality is good. But if you are trying to listen to distant or low-powered station, there’s a lot of competition. Our modern world is awash in a soup of electronic interference. [Electronics Unmessed] tells — and shows — us how much noise can show up on a SDR setup and what simple things you can do to improve it, sometimes tremendously.

According to the video, the main culprit in these cases is the RF ground path. If you have a single antenna wire, there still has to be a ground path somewhere and that may be through the power line or through, for example, a USB cable, the host computer, and its power supply. Unsurprisingly, the computer is full of RF noise which then gets into your receiver.

Adding a counterpoise makes a marked difference. A low inductance ground connection can also help. The counterpoise, of course, won’t be perfect, so to further turn down the noise, ferrite cores go around wires to block them from being ground paths for RF.

The common cores you see are encased in plastic and allow you to snap them on. However, using a bare core and winding through it multiple times can provide better results. Again, thanks to the SDR’s display, you can see the difference this makes in his setup.

None of this is new information, of course. But the explanation is clear, and being able to see the results in a spectrum display is quite enlightening. Those cores essentially turn your wire into a choke. People think that grounding is simple, but it is anything but.

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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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The VLF Transformation

August 19, 2025 by 6 Comments

People have long been interested in very low frequency (VLF) radio signals. But it used to be you pretty much had to build your own receiver which, luckily, wasn’t as hard as building your own VHF or UHF gear. But there is a problem. These low frequencies have a very long wavelength and, thus, need very large antennas to get any reception. [Electronics Unmessed] says he has an answer.

These days, if you want to explore any part of the radio spectrum, you can probably do it easily with a software-defined radio (SDR). But the antenna is the key part that you are probably lacking. A small antenna will not work well at all. While the video covers a fairly common idea: using a loop antenna, his approach to loops is a bit different using a matching transformer, and he backs his thoughts up with modeling and practical results.

Of course, transformers also introduce loss, but — as always — everything is a trade-off. Running hundreds of feet of wire in your yard or even in a loop is not always a possibility. This antenna looks like it provides good performance and it would be simple to duplicate.

Early radio was VLF. Turns out, VLF may provide an unexpected public service in space.

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Sniffing 5G With Software-Defined Radio

August 18, 2025 by 3 Comments

The fifth generation mobile communications protocol (5G) is perhaps the most complicated wireless protocol ever made. Featuring wildly fast download speeds, beam forming base stations, and of course non-standard additions, it’s rather daunting prospect to analyze for the home hacker and researcher alike. But this didn’t stop the ASSET Research Group from developing a 5G sniffer and downlink injector.

The crux of the project is focused around real-time sniffing using one of two Universal Software Radio Peripheral (USRP) software-defined radios (SDRs), and a substantial quantity of compute power. This sniffed data can even be piped into Wireshark for filtering. The frequency is hard-coded into the sniffer for improved performance with the n78 and n41 bands having been tested as of writing. While we expect most of you don’t have the supported USRP hardware, they provided a sample capture file for anyone to analyze.

The other main feature of the project is an exploitation framework with numerous attack vectors developed by ASSET and others. By turning an SDR into a malicious 5G base station, numerous vulnerabilities and “features” can be exploited to with results ranging from downgrading the connection to 4G, fingerprinting and much more. It even includes an attack method we preciously covered called 5Ghull which can cause device failure requiring removal of the SIM Card. These vulnerabilities offer a unique look inside the inner workings of 5G.

If you too are interested in 5G sniffing but don’t have access to the hardware needed, check out this hack turning a Qualcomm phone into a 5G sniffer!

Walter Is A Tiny Cellular Modem For Your Projects

August 16, 2025 by 21 Comments

It wasn’t that long ago that projects with cellular connectivity were everywhere, but with 2G no longer universally available, glory days of cheap 2G modules seem to be on their way out. So when [Data Slayer] titled his video “You’ve Never Seen Cellular Like This” about a new GSM radio module, we couldn’t help but think that we have — and that we’re glad to see it back.

The module is the Walter, by DPTechnics out of Belgium. It’s fully open-source and contains a ESP32-S3 for WiFi and BLE plus a Sequans Monarch chip for GSM and GNSS connectivity. It’s not the blazing-fast 5G you’re paying your phone carrier for: this is an IoT modem, with LTE-M and NB-IoT. We’re talking speeds in the kbps, not Mbps– but we’re also talking very, very low power usage. Since it’s LTE-M rather than full LTE, you’re probably not going to be bringing back the golden days of Arduino Cellphones,  (since LTE-M doesn’t support VoLTE) but if LoRa isn’t your jam, and you hang out around cell towers, this level of connectivity might interest you.

Walter is actually a drop-in replacement for PyCom’s old GPy module, so if you had a project in mind for that and are frustrated by it being EoL — well, here you are. [Data Slayer] seemed impressed enough with its capabilities as a GPS tracker. We’re impressed with the 9.8 µA consumed in deep sleep mode, and the fact that it has already been certified with the CE, FCC, IC, RCM and UKCA. Those certs mean you could go from prototype to product without getting tangled in red tape, assuming Walter is the only radio onboard.

Our thanks to [Keith Olson] for phoning in the tip. If you have a tip and want to connect, operators are standing by. Continue reading “Walter Is A Tiny Cellular Modem For Your Projects” →