This great old video (embedded below the break) from Tektronix in the mid-60s covers a topic that seems to confuse folks more than it should — transmission lines. We found it on Paul Carbone’s blog, a great site for aficionados of old analog scopes in its own right.
As with many of these older videos, the pacing is a bit slow by today’s standards, but the quality of the material eventually presented more than makes it worth the effort to reign in your ADHD. For a preview, you can skip to the end where they do a review of all the material.
They start off 5:31 with a pulse travelling down a wire pair, and take a very real-world approach to figuring out the characteristic impedance of the line: if the pulse was created by a battery of 9V, how much current is flowing? If the DC resistance of the wire is zero then there should be an infinite current by Ohm’s law, and that’s clearly not happening. This motivates the standard analysis where you break the wire down into distributed inductance and capacitance.
Of course they do the experiment where you inject a pulse into a long loop of coaxial cable and play around with the termination at the other end of the line. They also measure the velocity factor of the line. Our only gripe is that they don’t tap the line in different places to demonstrate standing waves. The good news is that we’ve got YouTube (and [w3aew]) for that.
If you’ve got 23 minutes to spare, and are curious about transmission lines or just enjoy the soothing voice of a trained radio announcer reading out values of various termination resistors, this old gem is just the ticket. Enjoy!
Continue reading “Retrotechtacular: Transmission Lines”
By 2016, it is evident the FAX machine has peaked. Sure, you still see a few. There are even services that will let you send and receive FAXes via Internet–which could mean no FAX machine was involved at all. But looking back, you have to wonder where it all started. Most people had never seen a FAX machine until the late 1960s or early 1970s. It was 1980 before there was a standard. Some, like hams and weather service employees, were using them even earlier. But would it surprise you to know that the first experimental FAX machine appeared in 1843?
Wait a minute. Bell didn’t even build a telephone until 1875 (the patent issued in 1876). Turns out the first FAX machines didn’t work with a phone. They worked over a telegraph wire.
Continue reading “FAXing in 1843”
We think of digital communications as a modern invention. But the reality is that semaphores, smoke signals, and Aldis lamps are all types of digital communication. While telegraphs are not as old as smoke signals, they, too, are a digital mode. The problem with all of these is that they require the operator to learn some kind of code. People don’t like to learn code because it is difficult, and employers don’t like to pay high wages to trained operators.
In the late 1830s, a man named William Cooke proposed a complex telegraph to a railway company. The company didn’t care for it and asked for something simpler. The railway didn’t like that either, so Cooke joined up with Charles Wheatstone and patented something that was a cross between a telegraph and a Ouija board.
Continue reading “Digital Communications 1830s Style”
In this short but intense classic of corporate cinematography, we get to watch as the Pacific Bell central office in Glendale, California is converted to electronic switching in a 47-second frenzy of cable cutting in 1984.
In the 1970s and 1980s, conversion of telephone central office (CO) switch gear from older technologies such as crossbar (XBar) switches or step-by-step (SxS) gear to electronic switching systems (ESS) was proceeding apace. Early versions of ESS were rolling out as early as the 1950s, but telcos were conservative entities that were slow to adopt change and even slower to make changes that might result in service outages. So when the time finally came for the 35,000 line Glendale CO to cutover from their aging SxS gear to ESS, Pacific Bell retained Western Electric for their “Speedy Cutover Service.”
Designed to reduce the network outage time to a minimum, cuts like these were intricately planned and rehearsed. Prep teams of technicians marked the cables to be cut and positioned them for easy access by the cutters. For this cut, scaffolding was assembled to support two tiers of cutters. It looks like the tall guys got the upper deck, and the shorter techs – with hard hats – worked under them.
At 11PM on this cut night, an emergency coordinator verified that no emergency calls were in progress, and the cut began. In an intense burst of activity, each of the 54 technicians cut about 20 cables. Smiles widened as the cut accelerated, and sparks actually flew at the 35.7 second mark. When done, each tech turned around and knelt down so the supervisors knew when everyone was done. At least one tech couldn’t help but whoop it up when the cut was done. Who could blame him? It must have been a blast.
Continue reading “Retrotechtacular: Cut All the Cables in this Speedy Teleco Switch Upgrade”
Decades after the end of the space race, an American rocket took off from Cape Canaveral. This was a routine launch to send a communications satellite into orbit, but the situation was an historic first. The rocket in question was driven by a powerful Russian engine unlike any ever built in the States. Although this particular engine was new, the design dated back to the space age.
By the early 1960s, the Russians were leaps and bounds ahead of the United States in terms of space exploration. They had already launched Sputnik and sent Yuri Gagarin to orbit the Earth. All in all, the Russians seemed poised to send a man to the moon. Russian technology had the Americans worried enough to spy on them with satellites, and the images that came back revealed something spectacular. Out in the Kazakh desert, the Russians were building an enormous causeway and two launch pads. As it turns out, the US had every reason to be worried.
Continue reading “Russian Rocket Tech Comes In From the Cold”
Léon Theremin built his eponymous instrument in 1920 under Soviet sponsorship to study proximity sensors. He later applied the idea of generating sounds using the human body’s capacitance to other physical forms like the theremin cello and the theremin keyboard. One of these was the terpsitone, which is kind of like a full-body theremin. It was built about twelve years after the theremin and named after Terpsichore, one of the nine muses of dance and chorus from Greek mythology.
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We are living in the age of citizen journalism and the 24-hour news cycle. Reports about almost anything newsworthy can be had from many perspectives, both vetted and amateur. Just a few decades ago, people relied on daily newspapers, radio, and word of mouth for their news. On the brink of the television age, several radio stations in the United States participated in an experiment to broadcast news over radio waves. But this was no ordinary transmission. At the other end, a new type of receiver printed out news stories, line drawings, and pictures on a long roll of paper.
Radio facsimile newspaper technology was introduced to the public at the 1939 World’s Fair at two different booths. One belonged to an inventor named William Finch, and one to RCA. Finch had recently made a name for himself with his talking newspaper, which embedded audio into a standard newspaper in the form of wavy lines along the edges that were read by a special device.
Continue reading “Retrotechtacular: Electronic Publishing in the 1930s”