Shortwave radio is boring, right? Maybe not. You never know what intrigue and excitement you might intercept. We recently covered secret number stations, and while no one knows for sure exactly what their purpose is, it is almost surely involving cloaks and daggers. However, there’s been some more obvious espionage radio, like Radio Swan.
The swan didn’t refer to the animal, but rather an island just off of Honduras that, until 1972, was disputed between Honduras and the United States. The island got its name–reportedly–because it was used as a base for a pirate named Swan in the 17th century. This island also had a long history of use by the United States government. The Department of Agriculture used it to quarantine imported beef and a variety of government departments had weather stations there.
You might wonder why the United States claimed a tiny island so far away from its shores. It turns out, it was all about guano. The Guano Islands Act of 1856 allowed the president to designate otherwise unclaimed territory as part of the United States for the purpose of collecting guano which, in addition to being bird excrement, is also important because it contains phosphates used in fertilizer and gunpowder. (Honestly, you couldn’t make this stuff up if you tried.)
However, the most famous occupant of Swan Island was Radio Swan which broadcast on the AM radio band and shortwave. The station was owned by the Gibraltar Steamship Company with offices on Fifth Avenue in New York. Oddly, though, the company didn’t actually have any steamships. What it did have was some radio transmitters that had been used by Radio Free Europe and brought to the island by the United States Navy. Did I mention that the Gibraltar Steamship Company was actually a front for the Central Intelligence Agency (CIA)?
Continue reading “Swans, Pigs, and the CIA: An Unlikely Radio Story”
[Ashish] let us know about his experiments in recreating the earliest type of radio set: a spark-gap transmitter and iron-filings coherer. He goes through the historical development of the kit in great detail, so we’re just going to skip that part. Go read it yourself!
Instead, we’re going to tease you with the coolest part of the rig: the coherer. In [Ashish]’s build, it’s a piece of tubing with some iron filings between two bolts. When a sufficiently strong EM wave hits the filings, they stick together and bridge the gap between the bolts, allowing electricity to flow and light up an LED, for instance. You can see this in [Ashish]’s video below the break, along with kmore discussion of that coherer.
Continue reading “The First Radio Sets: a Spark Gap and a Coherer”
Direct conversion receivers are popular among ham radio operators and others who build radios. Suppose you want to listen to a signal at 7.1 MHz. With a direct conversion receiver, you’d tune a local oscillator to 7.1 MHz, and mix it with the incoming signal. The resulting sum and differences of the input frequencies will include the audio of an AM signal on the desired frequency.
Continue reading “Polyakov Direct Digital Synthesis Receiver”
[Alberto di Bene] wanted to build an SDR for relatively low frequencies. Usually, you’d start with some front end to get the radio frequency signal down where you can work with it. But [Alberto] practically just fed an antenna into an STM32F429 Discovery board and did all the radio processing in the onboard ARM chip.
There is a little more to it than that, but only a little. If you open the PDF file on [Alberto’s] site, you’ll see there is a simple front end filter (a transformer, along with a few capacitors and inductors). This low pass filter prevents high frequencies from reaching the ARM processor’s analog to digital converter. In addition, a capacitor and a couple of resistors ensure the converter only sees positive voltages.
The CPU digitizes the incoming signal and processes it, demodulating several different types of radio transmission. The recovered audio is sent through the onboard digital to analog converter.
In addition to an input filter, the output also needs a filter to prevent high frequencies from reaching the speaker. Unlike the input filter, this one is a bit more complicated. The inductors needed for a passive filter were too large to be practical, so the output filter is an active one with a few transistors. The only other external circuitry is the power supply for the Discovery board.
The document does a great job of explaining the rationale behind the design choices and how the whole system works. It also includes simulations of both analog and digital filters used in the design.
This is really bare metal SDR and reading the code is educational. However, if you want to start with something simpler, consider GNU Radio and either an SDRPlay or a cheap RTL-SDR dongle.
A few months ago, the Internet resounded with news that the FCC would ban open source router firmware. This threat came from proposed rules to devices operating in the U-NII bands – 5GHz WiFi, basically. These rules would have required all devices operating in this band to prevent modification to the radio inside these devices. Thanks to the highly integrated architecture of these devices, Systems-on-Chips, and other cost cutting measures from router manufacturers, the fear was these regulations would ultimately prevent modifications to these devices. It’s a legitimate argument, and a number of the keepers of the Open Source flame aired their concerns on the matter.
Now, the FCC has decided to clear the air on firmware upgrades to wireless routers. There was a fair bit of confusion in the original document, given the wording, “how [its] device is protected from ‘flashing’ and the installation of third-party firmware such as DD-WRT.” This appeared to mandate wholesale blocking of Open Source firmware on devices, with no suggestion as to how manufacturers would accomplish this impossible task.
[Julias Knapp], chief of the FCC’s Office of Engineering and Technology has since clarified the Commission’s position. In response to the deluge of comments to the FCC’s Notice of Proposed Rulemaking, the phrase, ‘protected from flashing… Open Source firmware” has been removed from the upcoming regulation. There’s new, narrow wording (PDF) in this version that better completes the Commission’s goal of stopping overpowered radios without encroching on the Open Source firmware scene. The people spoke, and the FCC listened — democracy at work.
One thing has stayed with the James Bond movie franchise through the decades: Mr. Bond always has the most wonderful of gadgets. Be it handheld, car-based, or otherwise, there’s always something to thrill that is mostly believable.
The biggest problem with all of those gadgets is that they mark Commander Bond as an obvious spy. “So Mr. Bond, I see you have a book with many random five character groups. Nothing suspicious about that at all!” And we all know that import/export specialists often carry exploding cufflinks or briefcases full of unknown electronics in hidden compartments.
Just as steganography hides data in plain sight, the best spy gadgets are the ones that don’t seem to be a spy gadget. It is no wonder some old weapons are little more than sticks or farm implements. You can tell a peasant he can’t have a sword, but it is hard to ban sticks.
Imagine you were a cold war era spy living in a hostile country with a cover job with Universal Exports. Would you rather get caught with a sophisticated encryption machine or an ordinary consumer radio? I’m guessing you went with the radio. You aren’t the only one. That was one of the presumed purposes to the mysterious shortwave broadcasts known as number stations. These were very common during the cold war, but there are still a few of them operating.
Continue reading “Secret Radio Stations by the Numbers”
Electronics leak waves and if you know what you’re doing you can steal people’s data using this phenomenon. How thick is your tinfoil hat? And you sure it’s thick enough? Well, it turns out that there’s a (secret) government standard for all of this: TEMPEST. Yes, all-caps. No, it’s not an acronym. It’s a secret codename, and codenames are more fun WHEN SHOUTED OUT LOUD!
The TEMPEST idea in a nutshell is that electronic devices leak electromagnetic waves when they do things like switch bits from ones to zeros or move electron beams around to make images on CRT screens. If an adversary can remotely listen in to these unintentional broadcasts, they can potentially figure out what’s going on inside your computer. Read on and find out about the history of TEMPEST, modern research, and finally how you can try it out yourself at home!
Continue reading “TEMPEST: a Tin Foil Hat for Your Electronics and Their Secrets”