The RFI Hunter: Looking For Noise In All The Wrong Places

Next time you get a new device and excitedly unwrap its little poly-wrapped power supply, remember this: for every switch-mode power supply you plug in, an amateur radio operator sheds a tear. A noisy, broadband, harmonic-laden tear.

The degree to which this fact disturbs you very much depends upon which side of the mic you’re on, but radio-frequency interference, or RFI, is something we should all at least be aware of. [Josh (KI6NAZ)] is keenly aware of RFI in his ham shack, but rather than curse the ever-rising noise floor he’s come up with some helpful tips for hunting down and eliminating it – or at least reducing its impact.

Attacking the problem begins with locating the sources of RFI, for which [Josh] used the classic “one-circuit-at-a-time” approach – kill every breaker in the panel and monitor the noise floor while flipping each breaker back on. This should at least give you a rough idea of where the offending devices are in your house. From there, [Josh] used a small shortwave receiver to locate problem areas, like the refrigerator, the clothes dryer, and his shack PC. The family flat-screen TV proved to be quite noisy too. Remediation techniques include wrapping every power cord and cable around toroids or clamping ferrite cores around them, both on the offending devices and in the shack. He even went so far as to add a line filter to the dryer to clamp down on its unwanted interference.

Judging by his waterfall displays, [Josh]’s efforts paid off, bringing his noise floor down from S5 to S1 or so. It’s too bad he had to take matters into his own hands – it’s not like the FCC and other spectrum watchdogs don’t know there’s a problem, after all.

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See You On The Dark Side Of The Moon: China’s Lunar Radio Observatory

For nearly as long as there has been radio, there have been antennas trained on the sky, looking at the universe in a different light than traditional astronomy. Radio astronomers have used their sensitive equipment to study the Sun, the planets, distant galaxies, and strange objects from the very edge of the universe, like pulsars and quasars. Even the earliest moments of the universe have been explored, a portrait in microwave radiation of the remnants of the Big Bang.

And yet with all these observations, there’s a substantial slice of the radio spectrum that remains largely a mystery to radio astronomers. Thanks to our planet’s ionosphere, most of the signals below 30 MHz aren’t observable by ground-based radio telescopes. But now, thanks to an opportunity afforded by China’s ambitious lunar exploration program, humanity is now listening to more of what the universe is saying, and it’s doing so from a new vantage point: the far side of the moon.

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All Your SDR Software In A Handy Raspberry Pi Image

The SDR revolution has brought a bonanza of opportunities for experimentation to the radio enthusiast, but with it has come a sometimes-confusing array of software for which even installation can be a difficult prospect for an SDR novice. If you’re bamboozled by it all then help may be at hand courtesy of [Luigi Cruz], who has packaged a suite of ready-to-go popular SDR software in an OS image for the Raspberry Pi.

On board the Raspbian-based OS image are SDR Angel, Soapy Remote, GQRX, GNURadio, LimeUtil, and LimeVNA. In hardware terms the RTL-SDR is supported, along with the LimeSDR, PlutoSDR, Airspy, and Airspy HF. All are completely ready-to-go and even have desktop shortcuts, so if the CLI scares you then you can still dive in and play. More importantly it’s designed for use with SDR transmitters as well as receivers, so the barrier for full SDR operation for radio amateurs has become significantly lower too.

This year has seen the seven-year anniversary of the RTL-SDR hack that probably did most to kickstart the use of SDRs in our community. Our colleague [Tom Nardi] wrote a retrospective that’s worth a look for its overview of some SDR tricks that have evolved over that time. Meanwhile if you don’t mind restricting your outlook somewhat, it’s possible to turn the Raspberry Pi 3 into an SDR all without any extra hardware.

WWII Aircraft Radio Roars To Life: What It Takes To Restore A Piece Of History

I’ve been told all my life about old-timey Army/Navy surplus stores where you could buy buckets of FT-243 crystals, radio gear, gas masks, and even a Jeep boxed-up in a big wooden crate. Sadly this is no longer the case. Today surplus stores only have contemporary Chinese-made boots, camping gear, and flashlights. They are bitterly disappointing except for one surplus store that I found while on vacation in the Adirondacks: Patriot of Lake George.

There I found a unicorn of historical significance; an un-modified-since-WW2 surplus CBY-46104 receiver with dynamotor. The date of manufacture was early-war, February 1942. This thing was preserved as good as the day it was removed from its F4F Hellcat. No ham has ever laid a soldering iron or a drill bit to it. Could this unit have seen some action in the south Pacific? Imagine the stories it could tell!

My unconventional restoration of this radio followed strict rules so as to minimize the evidence of repair both inside and out yet make this radio perform again as though it came fresh off the assembly line. Let’s see how I did.

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Restoring A 1949 Golden Throat Radio

[Mr. Carlson] has a really beautiful old 1949-era radio to restore and you can watch him do it in a comprehensive video, below. We aren’t sure what we were more amused by: the odd speaker that looks like a ceiling air vent or the sticker on the back certifying that the radio produces the tone of the “golden throat” signed by RCA’s chief engineer.

Electrically, the radio didn’t look that remarkable. Of course, the capacitors were presumed bad and replaced. The video made us remember how much we hated restringing dial radios!

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Hackaday Superconference: An Analog Engineer Dives Into RF

Those of us who work with electronics will usually come to the art through a particular avenue that we master while imbibing what we need from those around it. For example, an interest in audio circuitry may branch into DSP and microcontrollers as projects become more complex. Some realms though retain an aura of impossibility, a reputation as a Dark Art, and chief among them for many people is radio frequency (RF). Radio circuitry is often surprisingly simple, yet that simplicity conceals a wealth of complexity because the medium does not behave in the orderly manner of a relatively static analogue voltage or a set of low-frequency logic levels.

Chris Gammell is a familiar face to many Hackaday readers for his mastery of much electronic trickery, so it comes as something of a surprise to find that RF has been one of the gaps in his knowledge. In his talk at the Hackaday Superconference he took us through his journey into RF work, and the result is a must-watch for anyone with a curiosity about radio circuitry who didn’t know where to start.

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Zombies Ate Your Neighbors? Tell Everyone Through LoRa!

As popular as the post-apocalyptic Zombie genre is, there is a quite unrealistic component to most of the stories. Well, apart from the whole “the undead roaming the Earth” thing. But where are the nerds, and where is all the apocalypse-proof, solar-powered tech? Or is it exactly this lack of tech in those stories that serves as incentive to build it in the first place? Well, maybe it doesn’t have to be the end of the world to seek for ways to cope with a collapse of our modern communication infrastructure either. Just think of natural disasters — an earthquake or hurricane causing a long-term power outage for example. The folks at [sudomesh] tackle exactly this concern with their fully open source, off-grid, solar-powered, LoRa mesh network, Disaster Radio.

The network itself is built from single nodes comprising of a battery-backed solar panel, a LoRa module, and either the ESP8266 or ESP32 for WiFi connectivity. The idea is to connect to the network with your mobile phone through WiFi, therefore eliminating any need for additional components to actually use the network, and have the nodes communicate with each other via LoRa. Admittedly, LoRa may not be your best choice for high data rates, but it is a good choice for long-range communication when cellular networks aren’t an option. And while you can built it all by yourself with everything available on [sudomesh]’s GitHub page, a TTGO ESP32 LoRa module will do as well.

If the idea itself sounds familiar, we did indeed cover similar projects like HELPER and Skrypt earlier this year, showing that LoRa really seems to be a popular go-to for off-grid communication. But well, whether we really care about modern communication and helping each other out when all hell breaks loose instead of just primevally defending our own lives is of course another question.