When the USA entered World War Two, they lacked a powerful mobile communications unit. To plug this gap they engaged Hallicrafters, prewar manufacturers of amateur radio transmitters and receivers, who adapted and ruggedized one of their existing products for the application.
The resulting transmitter was something of a success, with production running into many thousands of units. Hallicrafters were justifiably proud of it, so commissioned a short two-part film on its development which is the subject of this article.
The transmitter itself was a very high quality device for the era, but even with the film’s brief insight into operating back in the AM era the radio aspect is not what should capture your interest. Instead of the radio it is the in-depth tour of an electronics manufacturing plant in the war years that makes this film, from the development process of a military product from a civilian one through all the stages of production to the units finally being fitted to Chevrolet K-51 panel vans and shipped to the front. Chassis-based electronics requiring electric hoists to move from bench to bench are a world away from today’s surface-mount micro-circuitry.
So sit back and enjoy the film, both parts are below the break.
When most of us think of forge work, the image that comes to our mind is likely to be a rather traditional one, of the village blacksmith’s shop, roaring coke-fired hearths, and an anvil ringing to the beat of hand-wielded hammers. Iron and steel, worked through the sweat of the human brow.
Precision metalwork probably doesn’t figure in there, yet there is another type of forging used to create some of the most highly stressed components on rockets, missiles, and aircraft as well as the more mundane ironwork of your garden fence. Drop forging allows reproducible shapes to be forged while maintaining tight control over the metallurgical properties of the finished product, exactly what is required for such high-performance applications.
The video below is a promotional film about drop forging in the aeronautical industry from the late 1950s, made for and about Wyman Gordon, still specialists in the field. With the charming optimism of the period and a very catchy title it goes into the detail of the plant, development, and quality control of a range of parts for the missiles and rockets of the day, and along the way shows the cutting edge of machine tooling in the days before CNC. A whole Periodic Table of metals are forged with an expertise probably not seen in many other places in the world.
There are also some sights you’d never see in today’s safety culture, for example a running press with men darting in to adjust the position of a forging while it is still moving. It’s not a short video, but definitely worth watching all the way through.
If you own a video projector, be it a module small enough to fit in a mobile phone or one designed for a cinema screen, the chances are it will have a DLP at its heart. An array of microscopic mirrors on an integrated circuit, the current state of the art in video projection technology.
Perhaps you own an older video projector, or maybe a cheaper new one. If so the chances are it’ll have a small LCD screen doing its work, taking the place of the Kodachrome in something very similar to your grandparents’ slide projector or their grandparents’ magic lantern.
LCD technology was invented in the 1970s, while DLP was invented at the end of the 1980s. So how did the video projectors that were such a staple of televised spectaculars in the preceding decades work? For that matter, how did NASA project their status displays on the huge screen at Mission Control? Certainly not with CRT technology, even the brightest CRT projectors weren’t up to filling a cinema-sized screen.
The answer came from the Eidophor (Greek: ‘eido’ and ‘phor’, ‘image’ and ‘bearer’), a device invented in the years before World War II by the Swiss physicist Dr. Fritz Fischer and granted a US patent in 1945. It featured a complex vacuum device in which an electron gun painted the video frames as a raster on an oil-covered mirror in the light path of a fairly conventional projector. High-voltage electric charges have the effect of deforming the surface of mineral oils, and it was this effect that was exploited to vary the effectiveness of the mirror as the raster was drawn. An unfortunate side-effect of tracing an oil surface with an electron beam is that a charge will build up on the oil surface, so the entire oil-covered mirror assembly had to rotate within its vacuum enclosure and pass under an electrode which removed any charge build-up.
You will probably be unaware of the exact date you last saw an eidophor performance. Quince Imaging tell us their last one was used at the TWA Dome in St Louis in July 2000. Eidophores may have become more compact over the decades but they remained costly to run, and through the 1990s they were suplanted by DLP devices that did substantially the same job with a lot less fuss.
It is not often that a search in the Hackaday archives for a technology returns no results, but the eidophor is one of those cases. Perhaps that is a fitting epitaph for a device that created its own show but never starred in it, that it is only its spectacular performances that live on.
If you read our recent feature about the Tal-y-Llyn Railway, the world’s first preserved line, you may have taken a while to watch the short film about the railway in the early 1950s. It was the work of an American film maker, [Carson “Kit” Davidson].
His other work includes some films that might be of interest to Hackaday readers, including one filmed in 1977: “100 Watts 120 Volts”. In it, he follows the manufacture of Duro-Test 100-watt light bulbs through all the stages of their assembly as neck, filament and envelope are brought together in strangely beautiful twentieth century production machinery.
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!
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.
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.