Radio Apocalypse: The GWEN System

Recent developments on the world political stage have brought the destructive potential of electromagnetic pulses (EMP) to the fore, and people seem to have internalized the threat posed by a single thermonuclear weapon. It’s common knowledge that one bomb deployed at a high enough altitude can cause a rapid and powerful pulse of electrical and magnetic fields capable of destroying everything electrical on the ground below, sending civilization back to the 1800s in the blink of an eye.

Things are rarely as simple as the media portray, of course, and this is especially true when a phenomenon with complex physics is involved. But even in the early days of the Atomic Age, the destructive potential of EMP was understood, and allowances for it were made in designing strategic systems. Nowhere else was EMP more of a threat than to the complex web of communication systems linking far-flung strategic assets with central command and control apparatus. In the United States, one of the many hardened communications networks was dubbed the Groundwave Emergency Network, or GWEN, and the story of its fairly rapid rise and fall is an interesting case study in how nations mount technical responses to threats, both real and perceived. Continue reading “Radio Apocalypse: The GWEN System”

Skin (Effect) in the Game

We love to pretend like our components are perfect. Resistors don’t have capacitance or inductance. Wires conduct electricity perfectly. The reality, though, is far from this. It is easy to realize that wire will have some small resistance. For the kind of wire lengths you usually encounter, ignoring it is acceptable. If you start running lots of wire or you are carrying a lot of current, you might need to worry about it. Really long wires also take some time to get a signal from one end to the other, but you have to have a very long wire to really worry about that. However, all wires behave strangely as frequency goes up.

Of course there’s the issue of the wire becoming a significant part of the signal’s wavelength and there’s always parasitic capacitance and inductance. But the odd effect I’m thinking of is the so-called skin effect, first described by [Horace Lamb] in 1883. [Lamb] was working with spherical conductors, but [Oliver Heaviside] generalized it in 1885.

Put simply, when a wire is carrying AC, the current will tend to avoid traveling in the center of the wire. At low frequencies, the effect is minimal, but as the frequency rises, the area in the center that isn’t carrying current gets larger. At 60 Hz, for example, the skin depth for copper wire — the depth where the current falls below 1/e of the value near the surface — is about 0.33 inches. Wire you are likely to use at that frequency has a diameter less than that, so the effect is minimal.

However, consider a 20 kHz signal — a little high for audio unless you are a kid with good ears. The depth becomes about 0.018 inches. So wire bigger than 0.036 inches in diameter will start losing effective wire size. For a 12-gauge wire with a diameter of 0.093 inches, that means about 25% of the current-handling capacity is lost. When you get to RF and microwave frequencies, only the thinnest skin is carrying significant current. At 6 MHz, for example, copper wire has a skin depth of about 0.001 inches. At 1 GHz, you are down to about 0.000081 inches. You can see this (not to scale) in the accompanying image. At DC, all three zones of the wire carry current. At a higher frequency, only the outer two zones carry significant current. At higher frequencies, only the outer zone is really carrying electrons.

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Joan Feynman Found Her Place in the Sun

Google ‘Joan Feynman’ and you can feel the search behemoth consider asking for clarification. Did you mean: Richard Feynman? Image search is even more biased toward Richard. After maybe seven pictures of Joan, there’s an endless scroll of Richard alone, Richard playing the bongos, Richard with Arline, the love of his life.

Yes, Joan was overshadowed by her older brother, but what physicist of the era wasn’t? Richard didn’t do it on purpose. In fact, no one supported Joan’s scientific dreams more than he did, not even their mother. Before Richard ever illuminated the world with his brilliance, he shined a light on his little sister, Joan.

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Can Commodity RC Controllers Stay Relevant?

Visualize some radio controlled airplane fanatic of yesteryear, with the requisite giant controller hanging from a strap, neck craned to see the buzzing dot silhouetted against the sky. It’s kind of a stereotype, isn’t it? Those big transmitters were heavy, expensive, and hard to modify, but that was just part of the challenge. Additionally, the form factor has to a degree remained rigid: the box with gimbals — or for the 3-channel controller, the pistol-grip with the big pot that looks like a cheesy race car wheel.

With so much changing in RC capabilities, and the rise of custom electronics across so many different applications, can commodity RC controllers stay relevant? We’re facing an age where the people who invest most heavily in RC equipment are also the ones most likely to want, and know how to work with customization for their rapidly evolving gear. It only makes sense that someone will rise up to satisfy that need.

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The Database of the Time Lords

Time zones have been a necessity since humans could travel faster than a horse, but with computers, interconnected over a vast hive of information, a larger problem has emerged. How do you keep track of time zones? Moreover, how do you keep track of time zones throughout history?

Quick question. If it’s noon in Boston, what time is it in Phoenix? Well, Boston is in the Eastern time zone, there’s the Central time zone, and Phoenix is in the Mountain time zone; noon, eleven, ten. If it’s noon in Boston, it’s ten o’clock AM in Phoenix. Here’s a slightly harder question: if it’s noon in Boston, what time is it in Phoenix during Daylight Savings Time? Most of Arizona doesn’t observe Daylight Savings Time, so if it’s noon in Boston, it’s 9 AM in Phoenix. What about the Navajo Nation in the northwestern part of Arizona? Here, Daylight Savings Time is observed. You can’t even make a rule that all of Arizona is always on Mountain Standard Time.

Indiana is another example of bizarre time zones. For most of the 20th century, Indiana was firmly in the Central time zone. Starting in the 1960s, the line between Eastern and Central time slowly moved west from the Ohio border. Some countries opted not to observe Daylight Savings Time. In 2006, the entire state started to observe DST, but the northwest and southwest corners of the state remained firmly in the Central time zone. The odd geographic boundaries of time zones aren’t limited to the United States, either; Broken Hill, New South Wales, Australia is thirty minutes behind the rest of New South Wales.

Working out reliable answers to all of these questions is the domain of the Time Zone Database, a catalog of every time zone, time zone change, and every strange time-related political argument. It records Alaska’s transition from the Julian to the Gregorian calendar. It describes an argument in a small Michigan town in 1900. It’s used in Java, nearly every kind of Linux, hundreds of software packages, and at least a dozen of the servers and routers you’re using to read this right now.

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Goodbye, TechShop

The CEO of TechShop, [Dan Woods], has hit the legal E-stop and declared Chapter-7 bankruptcy for the business. All ten US locations were shuttered on Wednesday with absolutely no advance warning. You can read the full statement from [Dan] here.

We are deeply saddened to hear of TechShop’s closing, and while it wasn’t implausible that this might happen someday, the abrupt shuttering must come as a painful shock to many for whom TechShop was an important part of their personal and professional lives. We owe a lot to the work and effort they put forth; they led the way as a pioneering makerspace and for more than ten years, TechShop provided access to tools, taught classes, and created opportunities for the DIY world that are still as important today as they were in the mid-aughts.

Leading the Way

Jim Newton, founder of TechShop, originally wanted a space to tinker with his pet projects. “I’m a frustrated inventor who needs to have access to this kind of stuff. And people always say that the best companies are the ones where the founders are passionate about what they are creating, which is exactly what I am,” Jim said in an interview in 2007, at the beginnings of TechShop.

It turned out that there were a lot of other tinkerers who wanted to work their pet projects too.

TechShop took a risk. All new business ventures are risky and most fail quite quickly, but in 2006, this whole movement, this idea that people could build things and take advantage of new technologies, personal fabrication, ad-hoc manufacturing, and rapid prototyping outside of universities and commercial R&D labs, was just a dream.

Adafruit was incubating in Limor’s dorm room. Arduino was just the name of some pub in Italy. Eben Upton was wiring prototype Raspberry Pi’s by hand. Nathan Seidle was still reflowing Sparkfun’s boards with a toaster oven. Maker Faire, “The World’s Largest Show and Tell,” wouldn’t even launch until the following year.

In the fading light of high school shop classes, people often were shown the ways of woodworking, light metalwork, and maybe how to fix a car or two. Filling a business with a smorgasbord of advanced machinery and teaching people how to use it, was, and still is, a relatively new concept. TechShop had a dream and made it real with the dedication of hardworking support staff and instructors around the country. Continue reading “Goodbye, TechShop”

Radio Apocalypse: The Emergency Broadcast System

Some sounds are capable of evoking instant terror. It might be the shriek of a mountain lion, or a sudden clap of thunder. Whatever your trigger sound, it instantly stimulates something deep in the lizard brain that says: get ready, danger is at hand.

For my part, you can’t get much scarier than the instantly recognizable two-tone alert signal (audio link warning) from the Emergency Broadcast System (EBS). For anyone who grew up watching TV in the 60s and 70s in the US, it was something you heard on at least a weekly basis, with that awful tone followed by a grave announcement that “the broadcasters of your area, in voluntary cooperation with the FCC and other authorities, have developed this system to keep you informed in the event of an emergency.” It was a constant reminder that white-hot death could rain from the sky at any moment, and the idea that the last thing you may ever hear was that tone was sickening.

While I no longer have a five-year-old’s response to that sound, it’s still a powerful reminder of a scary time. And the fact that it’s still in use today, at least partially, seems like a good reason to look at the EBS in a little more depth, and find out the story behind the soundtrack of the end of the world.

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