Radio Hacks

1329 Articles

A DIY EMC Probe From Semi-Rigid Coax And An SDR

April 24, 2019 by 17 Comments

Do you have an EMC probe in your toolkit? Probably not, unless you’re in the business of electromagnetic compatibility testing or getting a product ready for the regulatory compliance process. Usually such probes are used in anechoic chambers and connected to sophisticated gear like spectrum analyzers – expensive stuff. But there are ways to probe the electromagnetic mysteries of your projects on the cheap, as this DIY EMC testing setup proves.

As with many projects, [dimtass]’ build was inspired by a video over on EEVblog, where [Dave] made a simple EMC probe from a length of semi-rigid coax cable. At $10, it’s a cheap solution, but lacking a spectrum analyzer like the one that [Dave] plugged his cheap probe into, [dimtass] went a different way. With the homemade probe plugged into an RTL-SDR dongle and SDR# running on a PC, [dimtass] was able to get a decent approximation of a spectrum analyzer, at least when tested against a 10-MHz oven-controlled crystal oscillator. It’s not the same thing as a dedicated spectrum analyzer – limited bandwidth, higher noise, and not calibrated – but it works well enough, and as [dimtass] points out, infinitely hackable through the SDR# API. The probe even works decently when plugged right into a DSO with the FFT function running.

Again, neither of these setups is a substitute for proper EMC testing, but it’ll probably do for the home gamer. If you want to check out the lengths the pros go through to make sure their products don’t spew signals, check out [Jenny]’s overview of the EMC testing process.

[via RTL-SDR.com]

Piezoelectric Antennas For Very, Very Low Frequencies

April 16, 2019 by 40 Comments

If you want to talk about antennas, the amateur radio community has you covered, with one glaring exception. Very low frequency and Extremely Low Frequency radio isn’t practiced very much, ultimately because it’s impractical and you simply can’t transmit much information when your carrier frequency is measured in tens of Hertz. There is more information on Extremely Low Frequency radio in Michael Crichton’s Sphere than there is in the normal parts of the Internet. Now there might be an easier way to play with VLF radiation, thanks to developers at the National Accelerator Laboratory. They’ve developed a piezoelectric transmitter for very long wavelengths.

Instead of pushing pixies through an antenna, this antenna uses a rod-shaped crystal of lithium niobate, a piezoelectric material. An AC voltage is applied to the rod makes it vibrate, and this triggers an oscillating electric current flow that’s emitted as VLF radiation. The key is that it’s these soundwaves bouncing around that define the resonant frequency, and the speed of sound in lithium niobate is a lot slower than the speed of light, but they’re translated into electric signals because of its piezoelectricity. For contrast, if this were a wire quarter-wave antenna it would be tens of kilometers long.

The application for this sort of antenna is ideally for where regular radio doesn’t work. Radio doesn’t work underwater, but nuclear subs trail an antenna out of the back to receive messages using Extremely Low Frequency radio. A walkie talkie doesn’t work in a mine, and this could potentially be used there. There is a patent for this piezoelectric antenna, so if anyone knows of a source of lithium niobate, put a link in the comments.

We’ve seen this trick before to make small antennas even smaller, but this is the first time we’ve seen it used in the VLF band, where it’s arguably even more impressive.

The $50 Ham: Checking Out The Local Repeater Scene

April 11, 2019 by 24 Comments

So far in this series, we’ve covered the absolute basics of getting on the air as a radio amateur – getting licensed, and getting a transceiver. Both have been very low-cost exercises, at least in terms of wallet impact. Passing the test is only a matter of spending the time to study and perhaps shelling out a nominal fee, and a handy-talkie transceiver for the 2-meter and 70-centimeter ham bands can be had for well under $50. If you’re playing along at home, you haven’t really invested much yet.

The total won’t go up much this week, if at all. This time we’re going to talk about what to actually do with your new privileges. The first step for most Technician-class amateur radio operators is checking out the local repeaters, most of which are set up exactly for the bands that Techs have access to. We’ll cover what exactly repeaters are, what they’re used for, and how to go about keying up for the first time to talk to your fellow hams.

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A New Digital Mode For Radio Amateurs

March 31, 2019 by 65 Comments

There used to be a time when amateur radio was a fairly static pursuit. There was a lot of fascination to be had with building radios, but what you did with them remained constant year on year. Morse code was sent by hand with a key, voice was on FM or SSB with a few old-timers using AM, and you’d hear the warbling tones of RTTY traffic generated by mechanical teletypes.

By contrast the radio amateur of today lives in a fast-paced world of ever-evolving digital modes, in which much of the excitement comes in pushing the boundaries of what is possible when a radio is connected to a computer. A new contender in one part of the hobby has come our way from [Guillaume, F4HDK], in the form of his NPR, or New Packet Radio mode.

NPR is intended to bring high bandwidth IP networking to radio amateurs in the 70 cm band, and it does this rather cleverly with a modem that contains a single-chip FSK transceiver intended for use in licence-free ISM band applications. There is an Ethernet module and an Mbed microcontroller board on a custom PCB, which when assembled produces a few hundred milliwatts of RF that can be fed to an off-the-shelf DMR power amplifier.

Each network is configured around a master node intended to use an omnidirectional antenna, to which individual nodes connect. Time-division multiplexing is enforced by the master so there should be no collisions, and this coupled with the relatively wide radio bandwidth of the ISM transceiver gives the system a high usable data bandwidth.

Whether or not the mode is taken up and becomes a success depends upon the will of individual radio amateurs. But it does hold the interesting feature of relying upon relatively inexpensive parts, so the barrier to entry is lower than it might be otherwise. If you are wondering where you might have seen [F4HDK] before, we’ve previously brought you his FPGA computer.

Bidirectional IP With New Packet Radio

March 30, 2019 by 24 Comments

There are a few options if you want to network computers on amateur radio. There are WiFi hacks of sort, and of course there’s always packet radio. New Packet Radio, a project from [f4hdk] that’s now on hackaday.io, is unlike anything we’ve seen before. It’s a modem that’s ready to go, uses standard 433 ISM band chips, should only cost $80 to build, and it supports bidirectional IP traffic.

The introductory documentation for this project (PDF) lays out the use case, protocol, and hardware for NPR. It’s based on chips designed for the 433MHz ISM band, specifically the SI4463 ISM band radio from Silicon Labs. Off the shelf amplifiers are used, and the rest of the modem consists of an Mbed Nucleo and a Wiznet W5500 Ethernet module. There is one single modem type for masters and clients. The network is designed so that a master serves as a bridge between Hamnet, a high-speed mesh network that can connect to the wider Internet. This master connects to up to seven clients simultaneously. Alternatively, there is a point-to-point configuration that allows two clients to connect to each other at about 200 kbps.

Being a 434 MHz device, this just isn’t going to fly in the US, but the relevant chip will work with the 915 MHz ISM band. This is a great solution to IP over radio, and like a number of popular amateur radio projects, it started with the hardware hackers first.

Executing A Vehicle Keyless Entry Attack

March 30, 2019 by 1 Comment

You read about well-publicised security exploits, but they always seem to involve somebody with a deity’s grasp of whatever technology is being employed, as well as a pile of impossibly exotic equipment. Surely a mere mortal could never do that!

Happily, that’s not always the case, and to prove it [Gonçalo Nespral] replicated an attack against RF devices such as some garage doors and motor vehicle locks that use a rolling code. His inspiration came from a device from2015, that encouraged the owner of a key to keep transmitting fresh codes. It did this by swamping the receiver of the car, garage door, or whatever with a strong slightly off frequency signal. This would cause the lock to not work, so the user would try again and again. The attacker listens with a very narrow bandwidth receiver on-frequency that is good enough to reject the jamming signal, and can harvest a sequence of the rolling codes enough to compromise it.

[Gonçalo]’s set-up uses a YARD stick One transceiver dongle as its transmitter, and an RTL-SDR for receive. A GNU Radio setup is used to retrieve the key data, and some custom Python code does the remaining work. We wouldn’t advocate using this in the wild and it could conceivably also gain you access to another car with a flashing light on top, but it’s an interesting exposé of the techniques involved.

Rolling code keyfob attacks are something we covered a few years ago, back when these attacks were all shiny and new.

Emergency Neighbourhood Communications Courtesy Of HELPER

March 29, 2019 by 23 Comments

For many people, phone and Internet connectivity are omnipresent and always available. It’s possible to upload selfies from a Chinese subway, and search for restaurant reviews in most highway towns, all thanks to modern cellular connectivity. However, in emergencies, we’re not always so lucky. If towers fail or user demand grows too large, things can collapse all too quickly. It’s in these situations that HELPER aims to flourish.

HELPER stands for Heterogeneous Efficient Low Power Radio. It’s a radio system designed to operate in the absence of any infrastructure, creating a pop-up network to serve community needs in disaster areas. Users can share information about available resources, like water, gasoline and food, while emergency workers can coordinate their response and direct aid to those who need it.

It’s a system built around commonly available parts. Raspberry Pis run the back end software and communicate with individuals over WiFi, with LoRa radios handling the longer-range communication from node to node. Combining this communication ability with GPS location and stored map data allows users to more easily find resources and assistance when things go wrong. The journal article is freely available for those wishing to learn more about the project.

It’s a project which aims to keep people safe when conventional networks go down. The key is to remember that once disaster strikes, it’s usually too late to start distributing radio hardware – emergency gear should be in place well before things start to go south. Of course, there’s also the government side of the equation – in the USA, the Emergency Broadcast System is a great example of emergency communications done right. Video after the break.

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