High-Stakes Fox Hunting: The FCC’s Radio Intelligence Division In World War II

With few exceptions, amateur radio is a notably sedentary pursuit. Yes, some hams will set up in a national or state park for a “Parks on the Air” activation, and particularly energetic operators may climb a mountain for “Summits on the Air,” but most hams spend a lot of time firmly planted in a comfortable chair, spinning the dials in search of distant signals or familiar callsigns to add to their logbook.

There’s another exception to the band-surfing tendencies of hams: fox hunting. Generally undertaken at a field day event, fox hunts pit hams against each other in a search for a small hidden transmitter, using directional antennas and portable receivers to zero in on often faint signals. It’s all in good fun, but fox hunts serve a more serious purpose: they train hams in the finer points of radio direction finding, a skill that can be used to track down everything from manmade noise sources to unlicensed operators. Or, as was done in the 1940s, to ferret out foreign agents using shortwave radio to transmit intelligence overseas.

That was the primary mission of the Radio Intelligence Division, a rapidly assembled organization tasked with protecting the United States by monitoring the airwaves and searching for spies. The RID proved to be remarkably effective during the war years, in part because it drew heavily from the amateur radio community to populate its many field stations, but also because it brought an engineering mindset to the problem of finding needles in a radio haystack.

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Supercon 2024: How To Track Down Radio Transmissions

You turn the dial on your radio, and hear a powerful source of interference crackle in over the baseline noise. You’re interested as to where it might be coming from. You’re receiving it well, and the signal strength is strong, but is that because it’s close or just particularly powerful? What could it be? How would you even go about tracking it down?

When it comes to hunting down radio transmissions, Justin McAllister and Nick Foster have a great deal of experience in this regard. They came down to the 2024 Hackaday Superconference to show us how it’s done.

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You Can Make Your Own Ribbon Mic With A Gum Wrapper

There are lots of different types of microphone, with the ribbon microphone being one of the rarer ones. Commercial versions are often prized for their tone and frequency response. You can make your own too, as [Something Physical] demonstrates using a packet of chewing gum.

Yes, the ribbon in this microphone was literally gained from Airwaves Extreme gum. It’s got nothing to do with freshness or the special mintiness quotient of the material, though; just that it’s a conductive foil and it makes the YouTube video more interesting to watch.

The gum wrapper is first soaked in hot water and then acetone, such that the paper backing can be removed. The foil is then corrugated with a tube press with some baking paper used for protection during this delicate process. The “motor” of the ribbon microphone is then produced out of plexiglass, copper tape, and a pair of powerful magnets. The ribbon is then stretched between the magnets and clamped in place, acting as the part of the microphone that will actually vibrate in response to sound. As it vibrates in the magnetic field, a current is generated in response to the sound. From there, it’s just a matter of hooking up a custom-wound transformer to the wires leading to the “motor” and it’s ready to test. It works off the bat, but there is some noise. Adding shielding over the transformer and a proper enclosure helps to make the microphone more fit for purpose.

If you’ve ever wanted to experiment with microphone construction, it’s hard to go past the joy of building a simple ribbon mic. You can experiment at will with different sizes and materials, too; you needn’t just limit yourself to different brands of gum!

We’ve featured some other great mic builds over the years, too. Video after the break.

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Bubble Displays Make A Neat Retro Clock

In 2025 we are spoiled for choice when it comes to displays, with affordable LCDs, OLEDs, TFTs, and e-ink panels of all sizes only a few clicks away. But in decades past, such exotica were not on the menu for casual construction. Instead there were a range of LED seven segment displays which have now largely passed out of use.

Among them were HP’s bubble displays, assemblies of miniature LEDs on a PCB, topped with plastic bubble lenses. If you had a calculator in the 1970s it probably had one, but in the present, [Joshua Coleman] has incorporated one into a pleasingly retro digital clock.

Inside the 3D printed case is an ESP32 with a pair of 74HC595 shift registers to drive the display, and an 18650 battery with all associated charging and protection circuitry. It’s a surprisingly simple circuit, and the code is provided on the page. He makes an apology to non-Americans for his use of US date formats, but we think few readers will be unable to change it to reflect the only date format which really matters.

If you find a bubble display, hang on to it. They’re certainly something we’ve seen before here a few times.

Stamp breakout boards.

Stamp: Modular Breakout Boards For SMD Prototyping

[Kalesh Sasidharan] from Sciotronics wrote in to tell us about their project, Stamp: a modular set of template breakout boards designed to make prototyping with SMD components faster, easier, and more affordable. No breadboards, custom PCBs, or tangled jumper wires required. The project has blasted past its Kickstarter goal, and is on track to start shipping in September.

Stamp was created out of frustration with the traditional SMD prototyping workflow. Breadboards don’t support SMD parts directly, and using adapters quickly gets messy, especially when you need to iterate or modify a design. Ordering PCBs for every small revision just adds delay, and cost.

Stamp solves this by offering reusable template boards with commonly used SMD footprints. You place the main component on the front and the supporting components on the back. Many complete circuits, such as buck converters, sensor blocks, microcontrollers, and so on, can fit on a single 17.8 × 17.8 mm board.

Most Stamps feature custom castellated holes, designed for side-by-side or right-angle edge connections, enabling a modular, reconfigurable approach to circuit building. The plan is to make the designs fully open source, so that others can build or adapt them. Although many PCB manufacturers might not have the facilities to make the special castellated edges which are available on some Stamps.

Dave Jones from the EEVblog covered the Stamp on one of his recent Mailbag videos, which you can check out below. This isn’t the first time we’ve seen somebody promise to reinvent the breadboard, but we do appreciate the simplicity of this approach.

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Camera is seen on the left with an Arduino connected to the right

Look To The Sky With This Simple Plane Tracker

Do you ever get tired of stressing your neck looking for planes in the sky? Worry not! Here is a neat and cheap Arduino/Ras Pi project to keep your neck sore free! [BANK ANGLE] presents a wonderfully simple plane tracking system using an affordable camera and basic microcontrollers.

The bulk of the system relies on a cheap rotating security camera that gets dissected to reveal its internals. Here stepper control wires can be found and connected to the control boards required to allow an Arduino nano to tell the motors when and where to spin. Of course, the camera system doesn’t just look everywhere until it finds a plane, a Raspberry Pi takes in data from local ADS-B data to know where a nearby plane is.

After that, all that’s left is a nifty overlay to make the professional look. Combining all these creates a surprisingly capable system that gives information on the aircraft’s azimuth, elevation, and distance.

If you want to try your hand at making your own version of [BLANK ANGLE]’s tracker, check out his GitHub page. Of course, tracking planes gets boring after a while so why not try tracking something higher with this open-source star tracker?

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Hands-On: EufyMake E1 UV Printer

The modern hacker and maker has a truly incredible arsenal of tools at their disposal. High-tech tools like 3D printers, laser cutters, and CNC routers have all become commonplace, and combined with old standbys like the drill press and mini lathe, it sometimes seems like we’ve finally peaked in terms of what the individual is realistically capable of producing in their own home. But occasionally a new tool comes along, and it makes us realize that there are still avenues unexplored for the home gamer.

After spending the last few weeks playing with it, I can confidently say the eufyMake E1 UV printer is one of those tools. The elevator pitch is simple: with a UV printer, you can print anything on anything. As you can imagine, the reality is somewhat more complex, but the fact that you can toss a three dimensional object in the chamber and spray it with a high-resolution color image with a few button presses holds incredible creative potential. Enough that the Kickstarter for the $1,700 printer has already raised a mind-boggling $27 million at the time of this writing, with more than a month yet to go before crossing the finish line.

If you’re on the fence about backing the campaign, or just have doubts about whether or not the machine can do what eufyMake claims, I’ll put those concerns to rest right now — it’s the real deal. Even after using the machine for as long as I have, each time a print job ends, I find myself momentary taken aback by just how good the end result is. The technology inside this machine that not only makes these results possible, but makes them so easily obtainable, is truly revolutionary.

That being said, it’s not a perfect machine by any stretch of the imagination. While I never ran into an outright failure while using the eufyMake E1, there’s a fairly long list of issues which I’d like to see addressed. Some of them are simple tweaks which may well get sorted out before the product starts shipping this summer, while others are fundamental to the way the machine operates and could represent an opportunity for competitors.

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