In 1940, England was in a dangerous predicament. The Nazi war machine had been sweeping across Europe for almost two years, claiming countries in a crescent from Norway to France and cutting off the island from the Continent. The Battle of Britain was raging in the skies above the English Channel and southern coast of the country, while the Blitz ravaged London with a nightly rain of bombs and terror. The entire country was mobilized, prepared for Hitler’s inevitable invasion force to sweep across the Channel and claim another victim.
We’ve seen before that no idea that could possibly help turn the tide was considered too risky or too wild to take a chance on. Indeed, many of the ideas that sprang from the fertile and desperate minds of British inventors went on to influence the course of the war in ways they could never have been predicted. But there was one invention that not only influenced the war but has a solid claim on being its key invention, one without which the outcome of the war almost certainly would have been far worse, and one that would become a critical technology of the post-war era that would lead directly to innovations in communications, material science, and beyond. And the risks taken to develop this idea, the cavity magnetron, and field usable systems based on it are breathtaking in their scope and audacity. Here’s how the magnetron went to war.
Those who fancy themselves as infrastructure nerds find cell sites fascinating. They’re outposts of infrastructure wedged into almost any place that can provide enough elevation to cover whatever gap might exist in a carrier’s coverage map. But they’re usually locked behind imposing doors and fences with signs warning of serious penalty for unauthorized access, and so we usually have to settle for admiring them from afar.
Some folks, like [Mike Fisher] aka [MrMobile], have connections, though, and get to take an up close and personal tour of a couple of cell sites. And while the video below is far from detailed enough to truly satisfy most of the Hackaday crowd, it’s enough to whet the appetite and show off a little of what goes into building out a modern cell site. [Mike] somehow got AT&T to take him up to a cell site mounted in the belfry and steeple of the 178-year old Unitarian Church in Duxbury, Massachusetts. He got to poke around everything from the equipment shack with its fiber backhaul gear and backup power supplies to the fiberglass radome shaped to look like the original steeple that now houses the antennas.
Next he drove up to Mount Washington in New Hampshire, the highest point in the northeast US and home to a lot of wireless infrastructure. Known for having some of the worst weather in the world and with a recent low of -36°F (-38°C) to prove it, Mount Washington is brutal on infrastructure, to which the tattered condition of the microwave backhaul radomes attests.
We appreciate the effort that went into this video, but again, [Mike] leaves us wanting more details. Luckily, we’ve got an article that does just that.
Lasers are such a fundamental piece of technology today that we hardly notice them. So cheap that they can be given away as toys and so versatile that they make everything from DVD players to corneal surgery a reality, lasers are one of the building blocks of the modern world. Yet lasers were once the exclusive province of physicists, laboring over expansive and expensive experimental setups that seemed more the stuff of science fiction than workhouse tool of communications and so many other fields. The laser has been wildly successful, and the story of its development is an intriguing tale of observation, perseverance, and the importance of keeping good notes.
Almost exactly one year ago, [Kreosan] published a video detailing an EM “weapon” built out of three magnetrons, some batteries, and a taser. It all seemed a bit too good to be true, so [Allen] decided to try and replicate the results for himself.
[Kreosan]’s original video was impressive, showing everything from home stereos to a humble moped exploding when in the presence of their powerful device. However, many of those watching the video doubted the footage. Most criticism centered around the nature of the power supply to the magnetron falling short of the usual 700-1000W seen in a microwave oven.
[Allen] starts by experimenting with a single magnetron, successfully using it to light a compact fluorescent bulb at a range of a few centimeters. Scaling up to the full triple magnetron setup with a cardboard and foil feedhorn, [Allen] is, at best, able to crash a calculator at a distance of a few feet.
The microwaves cause no explosions, and the device doesn’t seem to have anywhere near the 50-foot range claimed by [Kreosan] for their device. [Allen] puts forth the theory that the explosions seen in the original footage are far more likely to be from small firecrackers rather than any electronic components dying from microwaves.
If you’ve been paying attention to the news, you may have seen a series of articles coming out about US staffers in Cuba. It seems that 21 staffers have suffered a bizarre array of injuries ranging from hearing loss to dizziness to concussion-like traumatic brain injuries. Some staffers have reported hearing incapacitating sounds in the embassy and in their hotel rooms. The reports range from clicking to grinding, humming, or even blaring sounds. One staffer described being awoken to a horrifically loud sound, only to have it disappear as soon as he moved away from his bed. When he got back into bed, the mysterious sound came back.
Cuba has denied any wrongdoing. However, the US has already started to take action – expelling two Cuban diplomats from the US in May. The question though is what exactly could have caused these injuries. The press has gone wild with theories of sonic weaponry, hidden bugs, and electronic devices, poisons, you name it. Even Julian Assange has weighed in, stating “The diversity of symptoms suggests that this is a pathogen combined with paranoia in an isolated diplomatic corps.”
Oscillators with components that aren’t electrically connected to anything? PCB traces that function as passive components based solely on their shape? Slots and holes in the board with specific functions? Welcome to the weird and wonderful world of microwave electronics, brought to you through this teardown and analysis of a Doppler microwave transceiver module.
We’ve always been fascinated by the way conventional electronic rules break down as frequency increases. The Doppler module that [Kerry Wong] chose to pop open, a Microsemi X-band transceiver that goes for about $10 on eBay right now, has vanishingly few components inside. One transistor for the local oscillator, one for the mixer, and about three other passives are the whole BOM. That the LO is tuned by a barium titanate slug that acts as a dielectric resonator is just fascinating, as is the fact that PB traces can form a complete filter network just by virtue of their size and shape. Antennas that are coupled to the transceiver through an air gap via slots in the board are a neat trick too.
[Kerry] analyzes all this in the video below and shows how the module can be used as a sensor. If you need a little more detail on putting these modules to work, we’ve got some basic circuits you can check out.
Because the universe is mostly made of hydrogen, H-line emissions are abundant, and their distribution can tell us a lot about the structure of galaxies. The 21-cm emission line is so characteristic and so prevalent that we used it as a unit of measurement on the plaques aboard the Pioneer probes as well as in the instructions for playing back the Voyager recordings. But listening in on 21-cm here on Earth requires a special setup, which [Adam (9A4QV)] describes in a detailed paper on the subject (PDF). [Adam] analyzes multiple configurations of LNAs and filters, both of which he sells, to determine the optimum front-end for 21-cm work. His analysis is a good primer on LNAs and explains why the front-end gear needs to be as close to the antenna as possible. Using his LNAs and filters and an SDR dongle, a reasonable 21-cm rig can be had for about $200 or so, less the antenna. He promises a follow-up paper on homebrew 21-cm antennas; we’ll be looking forward to that.
Not keen on the music of the spheres and prefer to listen to our own spacecraft instead? Then read up on the Deep Space Network and how you can snoop in.
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