How radios send and receive information can seem magical to the uninformed. For some people, this week’s Retrotechtacular video, “Frequency Modulation – Part 1 Basic Principles”, from the US Army Department of Defense 1964 will be a great refresher, and for others it will be their first introduction into the wonderful world of radio communications.
The stated objective is to teach why FM radio communication reduces interference which normally afflicts AM radio communications. Fundamentals of AM and FM is a better description, however, because the first part of the video nicely teaches the principles of AM and FM radio communications. It isn’t until later in the clip that it delves into interference, advantages of FM modulation, and detailed functioning of FM radio. The delivery is slow at times and admittedly long, yet the pace is perfect for a young ham to follow along with plenty of time to soak in the knowledge. If you’re still on the fence about becoming a ham here’s some words or encouragement.
Though the video isn’t aimed at ham radio users it does address core knowledge needed by amateur radio hobbyists. Amateur radio is full of many exciting communication technologies and you should have a clear understanding of AM and FM communication methodologies before getting on Grandpa’s information super highway. Once you have your ham license (aka ticket) you have privileges to create and test amazing ham related hacks, like [Lior] implementing full programmable control of a Baofeng UV5R ham radio using an Arduino.
Join us after the break to watch the video.
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These slides may not be the style of character art you remember from the days of 2400 baud modems; they’re more advanced than what was out there in the beginning. It turns out there is still some life left in this art subculture. For this week’s installment of Retrotechtacular we look in on [Doug Moore’s] talk on the history and survival of ANSI and ASCII art given at this year’s BSides conference.
ASCII is still a common character encoding so chances are you’re already familiar with it. ANSI on the other hand is a rather confusing term as it’s been lost in obscurity when referring to character sets. In this case it refers to a set of extended characters which is better described as Windows Code Pages.
Most of what we know about the ANSI art scene is from watching BBS: The Documentary (which is on our ten best hacking videos list). We certainly remember seeing the vertically scrolling art after connecting to a dial-up BBS back in the day. But understanding the factions that formed around the creation, bundling, and distribution of this is art is fascinating. [Doug] does a great job of covering this history, sharing side-by-side examples of the shunned practice of “ripping” another artists work. This image is actually not a rip. Later in his talk he discusses the continued existence of the subculture, showing what a modern take on the same subject looks like.
If you’re merely into the technical the first half of the video below is worth watching. But we bet it’ll be hard not to continue to the end for a side-trip into art history.
Retrotechtacular is a weekly column featuring hacks, technology, and kitsch from ages of yore. Help keep it fresh by sending in your ideas for future installments.
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This very stern looking gentleman is about to explain how voltage doubles work in a plodding, yet satisfyingly thorough manner.
We’re not certain when this US Air Training Command video was produced. Obviously it was used to train servicemen who were responsible for keeping electronics running during war time. We’re glad for that, as they really found just the right balance to present a concept that required some knowledge, but is approachable for even the most basic of new electronics hackers.
The demonstration board shown on the right is the voltage circuit highlighted in the lesson. Here the pointing stick is being used to trace out the circuit function during one phase of the input transformer. The capacitor/diode pairs rectify the voltage, with the capacitors discharging in
parallel series to double the output voltage. But how does the variable load (RL) affect the output? This is demonstrated under several different conditions using an oscilloscope to illustrate the change.
The discussion of how the diodes work reminded us of a modern tutorial we just ran across this weekend. It’s a bit bizarre, but explains the PN junction in a different way than we’re accustomed to. In this case you will already need to be familiar with how semiconductors work to understand the presentation.
Both clips can be found below the jump.
Continue reading “Retrotechtacular: Understanding a voltage doubler”
This is an overview of a 500,000 Watt radio transmitter site. It’s one of the slides shared in a guided video tour of the transmitter’s hardware. The radio station — whose call sign was WLW — called itself the Nation’s Station because of its ability to reach so much of the country.
It operated at the 500 kW level starting back in the 1930’s. The technology at the time meant that there were a lot of challenges involved with transmitting at this level of power. It took 750 kW input to achieve the 500 kW output. To reach that the station had a set of AC motors in the basement generating the 4500 Amps at 33 Volts DC
needed to power the transmitter to heat each filament. Obviously there was a lot of heat generated at the same time. The system was water-cooled. An elaborate network of Pyrex pipes carried distilled water to and from the tubes to handle the heat dissipation.
The video tour lasts about thirty minutes. It’s just packed with interesting tidbits from the experts leading the tour so add it to your watch list for some geeky entertainment over the weekend.
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Have you ever seen one of these SCELBI 8B computers? This is one of the first hobby computer kits which were sold starting in 1974.
This is just one of the many pieces of vintage computing hardware shown off in this playlist (the SCELBI is the fifth video). The collection is part of the Bugbook Historical Microcomputer Museum. [Dave Larsen], the curator of the collection, has been accumulating historic and often rare hardware for decades. More recently he’s been making video documentaries of the pieces and posting them for your enjoyment.
We love museums, but this is something different. [Dave’s] videos walk us through each exhibit, often filling in the story with anecdotes and insight from his own personal experience. It’s like a school field trip to the museum for those of us who can’t get enough of the moldy oldies.
We remember seeing at least one cool hack that used the 8008 processor also found in the computer pictured above. It was a clock built from a similar system.
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On this installment of Retrotechtacular we’re taking a look at the history of the United States Antiballistic Missile System. The cold war was a huge driver of technological development, and this missile defense is a good example. At its most basic this is a radar system capable of tracking objects in three dimensions. It utilizes separate transmitters and receivers which are synchronized to rotate at the same time.
The movie, which is about forty-five minutes, came to our attention because of [Dammitd’s] interest in the Luneburg Lens used by the system. At about 11:10 into the video after the break this component is discussed. Inside a dome like the one seen above is a reflector made of blocks of polystyrene foam which has been laced with bits of metal. This lens is stationary, with the receiver rotating around it to collect the transmitter’s waves as the echos bouncing off an object in the sky are focused by the lens.
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Here’s a really quick video which takes a different approach to understanding the Fourier Series than we’re used to. If you’re a regular reader we’re sure you’ve heard of the Fourier Series (often discussed as FFT or Fast Fourier Transform), but there’s a good chance you know little about it. The series allows you to break down complex signals (think audio waves) into combinations of simple sine or cosine equations which can be handled by a microcontroller.
We’ve had that base level of understanding for a long time. But when you start to dig deeper we find that it becomes a math exercise that isn’t all that intuitive. The video clip embedded after the break changes that. It starts off by showing a rotating vector. Mapping the tip of that vector horizontally will draw the waveform. The Fourier Series is then leveraged, adding spinning vectors for the harmonics to the tip of the last vector. The result of summing these harmonics produces the sine-based square wave approximation seen above.
That’s a mouthful, and we’re sure you’ll agree that the video demo is much easier to understand. But the three minute clip just scratches the surface. If you’re determined to master the Fourier Series give this mammoth Stanford lecture series on the topic a try.
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