dielectric

18 Articles

Shoot The Moon With This Homebrew Hardline RF Divider

March 31, 2020 by 21 Comments

You can say one thing for [Derek]’s amateur radio ambitions — he certainly jumps in with both feet. While most hams never even attempt to “shoot the Moon”, he’s building out an Earth-Moon-Earth, or EME, setup which requires this little beauty: a homebrew quarter-wave hardline RF divider, and he’s sharing the build with us.

For background, EME is a propagation technique using our natural satellite as a passive communications satellite. Powerful, directional signals can bounce off the Moon and back down to Earth, potentially putting your signal in range of anyone who has a view of the Moon at that moment. The loss over the approximately 770,000-km path length is substantial, enough so that receiving stations generally use arrays of high-gain Yagi antennas.

That’s where [Derek]’s hardline build comes in. The divider acts as an impedance transformer and matches two 50-ohm antennas in parallel with the 50-ohm load expected by the transceiver. He built his from extruded aluminum tubing as the outer shield, with a center conductor of brass tubing and air dielectric. He walks through all the calculations; stock size tubing was good enough to get into the ballpark for the correct impedance over a quarter-wavelength section of hardline at the desired 432-MHz, which is in the middle of the 70-cm amateur band. Sadly, though, a scan of the finished product with a NanoVNA revealed that the divider is resonant much further up the band, for reasons unknown.

[Derek] is still diagnosing, and we’ll be keen to see what he comes up with, but for now, at least we’ve learned a bit about homebrew hardlines and EME. Want a bit more information on Moon bounce? We’ve got you covered.

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Simple Acrylic Plates Make Kirlian Photography A Breeze

November 30, 2019 by 1 Comment

We know, we know – “Kirlian photography” is a term loaded with pseudoscientific baggage. Paranormal researchers have longed claimed that Kirlian photography can explore the mood or emotional state of a subject through the “aura”, an energy field said to surround and emanate from all living things. It’s straight-up nonsense, of course, but that doesn’t detract from the beauty of plasma aficionado [Jay Bowles]’ images produced by capacitive coupling and corona discharge.

Technically, what [Jay] is doing here is not quite Kirlian photography. The classic setup for “electrophotography” is a sandwich of photographic film, a glass plate, and a metal ground plate. An object with a high-voltage, high-frequency power supply attached is placed on top of the sandwich, and the resulting corona discharge exposes the film. [Jay]’s version is a thin chamber made of two pieces of solvent-welded acrylic and filled with water. A bolt between the acrylic panes conducts current from a Tesla coil – perhaps this one that we’ve featured before – into the water. When something is placed on the acrylic, a beautiful purple corona discharge streams out from the object.

It’s an eerie effect, and it’s easy to see how people can see an aura and attribute mystical properties to it. In the end, though, it’s not much different than touching a plasma globe, and just about as safe. Feeling a bit more destructive? Corona discharge is a great way to make art, both in wood and in acrylic.

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[Ben Krasnow] Makes A DSKY

May 19, 2019 by 6 Comments

There are hundreds if not thousands of artifacts from the Apollo program scattered around the globe, some twisted wrecks at the bottom of the ocean, others lovingly preserved and sitting in museums or in the hands of private collectors. All of what’s left is pretty much pure unobtainium, so if you want something Apollo-like, you’re probably going to have to make it yourself.

[Ben Krasnow] took up the challenge to make an electroluminescent Apollo-era DSKY display from scratch, with outstanding results. The DSKY, or “display and keyboard”, was the user interface for the Apollo Guidance Computer, the purpose-built digital navigation system that got a total of 24 men there and back again. [Ben] says it took a long time to recreate the display, and we can see why. He needed to master quite a few skills, including screen printing to get the glass-panel display working. The panel is a sandwich of phosphorescent paint, a dielectric, and conductive ink. The ink is silkscreened on the back to form the characters, all applied to indium tin oxide (ITO) conductive glass. A PCB with the same pattern of character segments lays behind that, driving each segment with 300 volts or so through a trio of HV507 high-voltage shift registers. It’s an impressive bit of engineering and gives off a decidedly not-homebrew vibe.

In the video below, [Ben] goes into detail about the trials he experienced on the way to this amazing endpoint, not least of which was frying chip after chip due to ineffective protection diodes in the shift registers. That’s an epic debugging story that’s worth the price of admission all by itself. It’s not the only DSKY in town, of course – [Fran Blanche] has been working on one for a while too – but there’s just something about that blue glow that we really like.

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The $50 Ham: Dummy Loads, Part 2

May 17, 2019 by 21 Comments

In the last installment of “The $50 Ham” I built a common tool used by amateur radio operators who are doing any kind of tuning or testing of transmitters: a dummy load. That build resulted in “L’il Dummy”, a small dummy load intended for testing typical VHF-UHF handy talkie (HT) transceivers, screwing directly into the antenna jack on the radio.

As mentioned in the comments by some readers, L’il Dummy has little real utility. There’s actually not much call for a dummy load that screws right into an HT, and it was pointed out that a proper dummy load is commercially available on the cheap. I think the latter observation is missing the point of homebrewing specifically and the Hackaday ethos in general, but I will concede the former point. That’s why at the same time I was building L’il Dummy, I was building the bigger, somewhat more capable version described here: Big Dummy.

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Video: Putting High Speed PCB Design To The Test

January 24, 2019 by 48 Comments

Designing circuit boards for high speed applications requires special considerations. This you already know, but what exactly do you need to do differently from common board layout? Building on where I left off discussing impedance in 2 layer Printed Circuit Board (PCB) designs, I wanted to start talking about high speed design techniques as they relate to PCBs.  This is the world of multi-layer PCBs and where the impedance of both the Power Delivery Network (PDN) and the integrity of the signals themselves (Signal Integrity or SI) become very important factors.

I put together a few board designs to test out different situations that affect high speed signals. You’ve likely heard of vias and traces laid out at right angles having an impact. But have you considered how the glass fabric weave in the board itself impacts a design? In this video I grabbed some of my fanciest test equipment and put these design assumptions to the test. Have a look and then join me after the break for more details on what went into this!

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A Look At Liquid Dielectrics

September 18, 2018 by 34 Comments

One evening quite a few years ago, as I was driving through my hometown I saw the telltale flashing lights of the local volunteer fire department ahead. I passed by a side road where all the activity was: a utility pole on fire. I could see smoke and flames shooting from the transformer and I could hear the loud, angry 60 Hz buzzing that sounded like a million hornet nests. As I passed, the transformer exploded and released a cloud of flaming liquid that rained down on the road and lawns underneath. It seemed like a good time to quit rubbernecking and beat it as fast as I could.

I knew at the time that the flaming liquid was transformer oil, but I never really knew what it was for or why it was in there. Oil is just one of many liquid dielectrics that are found in a lot of power distribution equipment, from those transformers on the pole to the big capacitors and switchgear in the local substation. Liquid dielectrics are interesting materials that are worth taking a look at.

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Low-Quality Capacitors Turned Into High-Quality Temperature Sensors

August 23, 2018 by 19 Comments

When life hands you a bunch of crummy capacitors, what do you do? Make a whole bunch of temperature sensors, apparently.

The less-than-stellar caps in question came to [pyromaniac303] by way of one of those all-in-one assortment kits we so love to buy. Stocked with capacitors of many values, kits like these are great to have around, especially when they’ve got high-quality components in them. But not all ceramic caps are created equal, and [pyromaniac303] was determined not to let the lesser-quality units go to waste. A quick look at the data sheets revealed that the caps with the Y5V dielectric had a suitably egregious temperature coefficient to serve as a useful sensor. A fleck of perf-board holds a cap and a series resistor; the capacitor is charged by an Arduino output pin through the resistor, and the time it takes for the input pin connected to the other side of the cap to go high is measured. Charge time is proportional to temperature, and a few calibration runs showed that the response is pretty linear. Unfortunately the temperature coefficient peaks at 10°C and drops sharply below that point, making the sensor useful only on one side of the peak. Still, it’s an interesting way to put otherwise unloved parts to use, and a handy tip to keep in mind.

Temperature sensing isn’t the only trick capacitors can do. We’ve seen them turned into touch sensors before, and used to turn a 3D-printer into a 3D-scanner.