Unraveling Radio Signals at Supercon 2024: Strategies for Locating Radio Broadcasts
Jamming the Airwaves: A Guide to Finding Mystery Transmissions
You flick the switch on your trusty radio, only to be greeted by a cacophony of unwanted static. You're intrigued by this potent source of interference spoiling your carefully tuned frequencies. You can hear it loud and clear, but is it close by or just overpowered? What's causing this disturbance? Just how do you track it down?
Enter Justin McAllister and Nick Foster, two radio sleuths extraordinaire who descended upon our Superconference in 2024 to give us a crash course in signal hunting.
From Interference to Insight
Nick Foster kicks off the talk by addressing the daunting task of discerning the truth behind the static-"Your hardware always lies to you," he warns. "We'll show you how the radio deceives you, the methods to combat it, and find out the real station you're sniffing around." Identifying what your radio is actually picking up-and where it's coming from-can be a challenging endeavor. "So, what exactly is this signal we're witnessing?" he wonders. "Is it a deliberate transmission from someone else? Could it be a result of a bad power supply or simply a birdie-an internal radio noise not present in the external environment?"
Several tools dominate the scene when it comes to sorting the signal from the noise. Justin briefly highlights popular hardware choices, such as the RX-888, a software-defined radio capable of being tuned across the HF, VHF, and UHF bands, as well as more affordable options like the Web-888, accessible via a web browser.Filters and various other SDRs are also valuable additions to your investigative kit.
To educatedly assume control over your reality, Justin explains, you must first establish a grounding in reality. "We turn our SDR on, plug in the antenna, and start scanning. But, are the signals we see truly real?" he queries. One obvious truth is that nobody makes money or communicates effectively using an unmodulated carrier-if all you see is a constant tone, it may well be real, but it's also likely not. It's often either unintended radiation, noise, or something internal to your hardware. Additionally, pay attention to whether you're looking at a fixed or variable frequency. Persistent lines on a spectrogram typically indicate intentional transmissions; intermittent squiggles, on the other hand, are more likely to be unintentional. Common culprits can include arc welders or noisy power supplies.
Real signals often exhibit a certain level of order, too. Justin points out that efficient use of the spectrum is a hallmark of human-made signals, with no gaps or repetition for no good reason. By analyzing the broader context of the signal, such as its frequency band, you can make educated guesses as to its origin. For instance, a signal you find on your garage door remote's frequency at 6 PM is likely coming from your neighbor's house. A useful technique when trying to identify nearby emitters is to flip switches ON and OFF, as this can help determine whether the signal is close by or not.
The RTL-SDR Dilemma
Nick Foster then takes the stage to discuss some of the unique challenges posed by the RTL-SDR. "One of the curses of the RTL-SDR is one of its strengths," Nick laments. "Its open front end means it can pick up and process a lot of nasty stuff but, unlike an analog receiver, it has nothing between the RF input and the ADC but an amplifier." Be aware of these potential pitfalls and keep them in mind when hunting for signals.
The talk then delves into finding and locating the source of transmissions, discussing techniques like multilateration-where synchronized receivers and math are used to measure time differences in the signal at each point to determine the transmitter's exact location. The talk also covers common sources of noise in residential environments, such as cheap PWM LED lights or knock-off laptop chargers, and discusses the impact of modern appliances on the noise floor.
In conclusion, Justin and Nick's entertaining and lighthearted take on radio investigation provides an excellent starting point for anyone looking to track down an elusive mystery transmitter. So, dig into their insights, and before you know it, you'll be catching those Red Herrings and White Rabbits like a pro!
Tools of the Trade
In the world of radio investigation, you'll need the right tools at your disposal. Here are some essential items to consider:
- Spectrum Analyzers: These devices are crucial for detecting and measuring the strength of radio signals across different frequencies. A visual representation of the signal spectrum helps to identify the frequency and strength of interfering signals.
- RF Detectors: Portable and easy to use, RF detectors are an excellent tool for quickly identifying radio signals and are often used in conjunction with spectrum analyzers.
- EMI Receivers: These specialized devices are designed to detect and measure electromagnetic interference, including unwanted radio signals. They can help in locating the source of such interference by analyzing the characteristics of the unwanted signals.
To effectively track down these pesky interfering signals, make use of these tools and techniques, deploy direction-finding methods, triangulate the transmitter's position, map signal strengths, and consult software tools for comprehensive analysis. Happy hunting!
In the pursuit of the mysterious transmission within the static-filled frequencies, Justin McAllister suggests incorporating data-and-cloud-computing resources into your hardware. He suggests tools like the RX-888, a software-defined radio, and the Web-888, accessible via a web browser, to sort the signal from the noise. Additionally, the RTL-SDR, with its unique challenges, can be complemented by technology that allows for multilateration, a technique used to pinpoint the exact location of transmitters by measuring time differences in the signal at each point.
