Radio Apocalypse: Meteor Burst Communications

The world’s militaries have always been at the forefront of communications technology. From trumpets and drums to signal flags and semaphores, anything that allows a military commander to relay orders to troops in the field quickly or call for reinforcements was quickly seized upon and optimized. So once radio was invented, it’s little wonder how quickly military commanders capitalized on it for field communications.

Radiotelegraph systems began showing up as early as the First World War, but World War II was the first real radio war, with every belligerent taking full advantage of the latest radio technology. Chief among these developments was the ability of signals in the high-frequency (HF) bands to reflect off the ionosphere and propagate around the world, an important capability when prosecuting a global war.

But not long after, in the less kinetic but equally dangerous Cold War period, military planners began to see the need to move more information around than HF radio could support while still being able to do it over the horizon. What they needed was the higher bandwidth of the higher frequencies, but to somehow bend the signals around the curvature of the Earth. What they came up with was a fascinating application of practical physics: meteor burst communications.

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What’s In A Washer?

Some things are so common you forget about them. How often do you think about an ordinary resistor, for example? Yet if you have a bad resistor, you’ll find it can be a big problem. Plus, how can you really understand electronics if you don’t know all the subtle details of a resistor? In the mechanical world, you could make the same arguments about the washer, and [New Mind] is ready to explain the history and the gory details of using washers in a recent video that you can see below.

The simple answer is that washers allow a bolt to fit in a hole otherwise too large, but that’s only a small part of the story. Technically, what you are really doing is distributing the load of a threaded fastener. However, washers can also act as spacers or springs. Some washers can lock, and some indicate various things like wear or preloading conditions.

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Rebooting An 1973 Art Installation Running On A Nova

Electronics-based art installations are often fleeting and specific things that only a select few people who are in the right place or time get to experience before they are lost to the ravages of ‘progress.’ So it’s wonderful to find a dedicated son who has recreated his father’s 1973 art installation, showing it to the world in a miniature form. The network-iv-rebooted project is a recreation of an installation once housed within a departure lounge in terminal C of Seattle-Tacoma airport.

You can do a lot with a ‘pi and a fistful of Teensies!

The original unit comprises an array of 1024 GE R6A neon lamps, controlled from a Data General Nova 1210 minicomputer. A bank of three analog synthesizers also drove into no fewer than 32 resonators. An 8×8 array of input switches was the only user-facing input. The switches were mounted to a floor-standing pedestal facing the display.

For the re-creation, the neon lamps were replaced with 16×16 WS2811 LED modules, driven via a Teensy 4.0 using the OctoWS2811 library. The display Teensy is controlled from a Raspberry Pi 4, hooked up as a virtual serial device over USB. A second Teensy (you can’t have too many Teensies!) is responsible for scanning a miniature 8×8 push button array as well as running a simulation of the original sound synthesis setup. Audio is pushed out of the Teensy using a PT8211 I2S audio DAC, before driving a final audio power amp.

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Simulating Cable TV

[Wrongdog Recons] suffers from a severe case of nostalgia. His earlier project simulated broadcast TV, and he was a little surprised at how popular the project was on GitHub. As people requested features, he realized that he could create a simulated cable box and emulate a 1990s-era cable TV system. Of course, you also needed a physical box, which turned into another project. You can see more about the project in the video below.

Inside is, unsurprisingly, a Raspberry Pi. Then you have to pretend to be a cable TV scheduler and organize your different video files for channels. You can interleave commercials and station breaks.

One addition was a scheduler so you could set up things like football games only play during football season. You can also control timing so you don’t get beer commercials during Saturday morning cartoons.

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Dollar bill validator

Reading The Color Of Money

Ever wondered what happens when you insert a bill into a vending machine? [Janne] is back with his latest project: reverse engineering a banknote validator. Curious about how these common devices work, he searched for information but found few resources explaining their operation.

To learn more, [Janne] explored the security features that protect banknotes from counterfeiting. These can include microprinting, UV and IR inks, holograms, color-shifting coatings, watermarks, magnetic stripes, and specialty paper. These features not only deter fraud but also enable validators to quickly verify a bill’s authenticity.

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Hackaday Links: May 11, 2025

Did artificial intelligence just jump the shark? Maybe so, and it came from the legal world of all places, with this report of an AI-generated victim impact statement. In an apparent first, the family of an Arizona man killed in a road rage incident in 2021 used AI to bring the victim back to life to testify during the sentencing phase of his killer’s trial. The video was created by the sister and brother-in-law of the 37-year-old victim using old photos and videos, and was quite well done, despite the normal uncanny valley stuff around lip-syncing that seems to be the fatal flaw for every deep-fake video we’ve seen so far. The victim’s beard is also strangely immobile, which we found off-putting.

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Open Source ELINT Accidentally From NASA

You normally think of ELINT — Electronic Intelligence — as something done in secret by shadowy three-letter agencies or the military. The term usually means gathering intelligence from signals that don’t contain speech (since that’s COMINT). But [Nukes] was looking at public data from NASA’s SMAP satellite and made an interesting discovery. Despite the satellite’s mission to measure soil moisture, it also provided data on strange happenings in the radio spectrum.

While 1.4 GHz is technically in the L-band, it is reserved (from 1.400–1.427 GHz)  for specialized purposes. The frequency is critical for radio astronomy, so it is typically clear other than low-power safety critical data systems that benefit from the low potential for interference. SMAP, coincidentally, listens on 1.41 GHz and maps where there is interference.

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