Where’s That Radio? A Brief History Of Direction Finding

August 19, 2021 by Al Williams 35 Comments

We think of radio navigation and direction finding as something fairly modern. However, it might surprise you that direction finding is nearly as old as radio itself. In 1888, Heinrich Hertz noted that signals were strongest when in one orientation of a loop antenna and weakest 90 degrees rotated. By 1900, experimenters noted dipoles exhibit similar behavior and it wasn’t long before antennas were made to rotate to either maximize signal or locate the transmitter.

British radio direction finding truck from 1927; public domain

Of course, there is one problem. You can’t actually tell which side of the antenna is pointing to the signal with a loop or a dipole. So if the antenna is pointing north, the signal might be to the north but it could also be to the south. Still, in some cases that’s enough information.

John Stone patented a system like this in 1901. Well-known radio experimenter Lee De Forest also had a novel system in 1904. These systems all suffered from a variety of issues. At shortwave frequencies, multipath propagation can confuse the receiver and while longwave signals need very large antennas. Most of the antennas moved, but some — like one by Marconi — used multiple elements and a switch.

However, there are special cases where these limitations are acceptable. For example, when Pan Am needed to navigate airplanes over the ocean in the 1930s, Hugo Leuteritz who had worked at RCA before Pan Am, used a loop antenna at the airport to locate a transmitter on the plane. Since you knew which side of the antenna the airplane must be on, the bidirectional detection wasn’t a problem.

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Charles Lindbergh The Famous… Inventor?

August 10, 2021 by Al Williams 25 Comments

Most people remember Charles Lindbergh for his non-stop solo flight across the Atlantic which made him an international celebrity. If you are a student of history, you might also know he was at the center of a very controversial trial surrounding the kidnapping of his child or even that he had a dance named after him. But did you know he was also the co-inventor of a very important medical device? Turns out, medicine can thank Lindbergh for the creation of the perfusion pump.

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Better Mousetraps (or Screw Drives) Don’t Always Win

August 4, 2021 by Al Williams 114 Comments

I’ve noticed, lately, that slotted screw heads are all but gone on new equipment. The only thing that I find remarkable about that is that it took so long. While it is true that slotted heads have been around for ages, better systems are both common and have been around for at least a century.

The reason slotted heads — technically known as the drive — are so common is probably because they are very easy to make. A hacksaw is sufficient for the job and there are other ways to get there, too. The only advantages I know of for the user is that you can easily clean a slotted drive and — possibly — use field expedient items like butter knives and quarters to turn the screw. I’ve heard people claim that it also is a feature that the screwdriver can pry things like paint can lids, but that’s a feature of the tool, not the screw drive.

The disadvantages, though, are significant. It is very hard to apply lots of torque to a slotted screw drive without camming it out or snapping the head off the screw. The screwdriver isn’t self-centering either, so applying force off-axis is common and contributes to the problem.

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Developing The First ICs In Orbit

July 31, 2021 by Jenny List 19 Comments

Over six decades of integrated circuit production we’ve become used to their extreme reliability and performance for a very reasonable price. But what about those first integrated circuits from the early 1960s? Commercial integrated circuits appeared in 1961, and recently Texas Instruments published a fascinating retrospective on the development of their first few digital ICs.

TI’s original IC product on the market was the SN502, a transistor flip-flop that debuted at $450 (about $4100 today), which caught the interest of NASA engineers who asked for logic functions with a higher performance level. The response was the development of the 51 series of logic chips, whose innovation included on-chip interconnects replacing the hand interconnects of the SN502. Their RCTL logic gave enough performance and reliability for NASA to use, and in late 1963 the Explorer 18 craft carried a telemetry system using the SN510 and SN514 chips into orbit. 52 and 53 series chips quickly followed, then in 1964 the 54 series TTL chips which along with their plastic-encapsulated 74 series equivalents are still available today.

Considering that in 1961 the bleeding edge of integrated circuit logic technology was a two-transistor chip with hand interconnects, it seems scarcely conceivable that by ten years later in 1971 the art had advanced to the point at which the first commercially available microprocessors would be produced. It’s unlikely that many of us will stumble upon any of the three-figure SN1-series logic chips, but to read about them is a fascinating reminder of this pivotal moment in the history of electronics.

Header: Mister rf, CC BY-SA 4.0.

Who Flew Across The Atlantic First? The Airborne Boats Of 1919

July 22, 2021 by Al Williams 47 Comments

Aviation history is a bit strange. People tend to remember some firsts but not others and — sometimes — not even firsts. For example, everyone knows Amelia Earhart attempted to be the first woman to fly around the globe. She failed, but do you know who succeeded? It was Jerrie Mock. How about the first person to do it? Wiley Post, a name largely forgotten by the public. Charles Lindbergh is another great example. He was the first person to fly across the Atlantic, right? Not exactly. The story of the real first transatlantic flight is one of aviation hacking by the United States Navy.

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Retrotechtacular: Nuvistor, Vacuum’s Last Gasp

July 21, 2021 by Jenny List 51 Comments

In 2021 all our electronics are solid state, in that they exclusively use semiconductor devices as their active components. Some of us may experiment with vacuum tubes, but only for curiosity or aesthetic purposes. Semiconductors have overtaken vacuum devices in all but the rarest of niche applications due to their easier design requirements, greater reliability, lower cost, and increased performance.

It was not always this way though, and there was a period at the start of the semiconductor era when transistors and vacuum tubes existed together side-by-side and competed directly. Vacuum tube manufacturers continued to create new devices into the 1970s, and in doing so they pushed the boundaries of their art in unprecedented directions. [David W Knight] has a page dedicated to the Nuvistor, something his calls the “final evolution of the thermionic valve”. His comparison photo seen above shows a Nuvistor on the left — a miniature vacuum tube you’ve likely never seen before.

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The Story Behind Ohm’s Law

July 20, 2021 by Al Williams 22 Comments

Do you ever wonder how much of what we do you could figure out from scratch? Tying your shoe might seem simple now, but kids have trouble mastering the skill, and dreaming it up for the first time is even harder. The same holds true for a lot of technology we use every day. Would you think up the computer mouse or even the computer if they didn’t already exist? Surely, though, one of the simplest and most useful math equations that is fundamental to electronics — Ohm’s law — would be easy to figure out, right? It is often the first thing you learn about electronics, but figuring it out that first time turned out to be quite difficult.

The fellow who discovered the relationship was Georg Ohm, a high school math and physics teacher from Köln. What you might not know is that the first time he published it, he got it wrong. But, lucky for us, he figured out his mistake and was able to correct it.

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