No-Etch: The Proof in the Bluetooth Pudding

In a previous episode of Hackaday, [Rich Olson] came up with a new no-etch circuit board fabrication method. And now, he’s put it to the test: building an nRF52 Bluetooth reference design, complete with video, embedded below.

The quick overview of [Rich]’s method: print out the circuit with a laser printer, bake a silver-containing glue onto the surface, repeat a few times to get thick traces, glue the paper to a substrate, and use low-temperature solder to put parts together. A potential drawback is the non-negligible resistance for the traces, but a lot of the time that doesn’t matter and the nRF52 reference design proves it.

The one problem here may be the trace antenna. [Rich] reports that it sends out a weaker-than-expected signal. Any RF design folks want to speculate wildly about the cause?

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Turning Television Into A Simple Tapestry

Teleknitting, the brainchild of Moscow artist [vtol], is an interesting project. On one hand, it doesn’t knit anything that is useful in a traditional sense, but on the other, it attempts the complex task of deconstructing broadcasted media into a simpler form of information transmission.

Teleknitting’s three main components are the processing and display block — made up of the antenna, Android tablet, and speaker — the dyeing machine with its ink, sponges, actuators, and Arduino Uno, and the rotating platform for the sacrificial object. A program running on the tablet analyzes the received signal and — as displayed on its screen — gradually halves the number of pixels in the image until there is only one left with a basic representation of the picture’s colour. From there, thread passes over five sponges which dye it the appropriate colour, with an armature that responds to the broadcast’s volume directing where the thread will bind the object.

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A Simple Yagi Antenna For Your Wi-Fi Router

When we take a new Wi-Fi router from its box, the stock antenna is a short plastic stub with a reverse SMA plug on one end. More recent and more fancy routers have more than one such antenna for clever tricks to extend their range or bandwidth, but even if the manufacturer has encased it in mean-looking plastic the antenna inside is the same. It’s a sleeve dipole, think of it as a vertical dipole antenna in which the lower radiator is hollow, and through which the feeder is routed.

These antennas do a reasonable job of covering a typical home, because a vertical sleeve dipole is omnidirectional. It radiates in all horizontal directions, or if you are a pessimist you might say it radiates equally badly in all horizontal directions. [Brian Beezley, K6STI] has an interesting modification which changes that, he’s made a simple Yagi beam antenna from copper wire and part of a plastic yoghurt container, and slotted it over the sleeve dipole to make it directional and improve its gain and throughput in that direction.

Though its construction may look rough and ready it has been carefully simulated, so it’s as good a design as it can be in the circumstances. The simulation predicts 8.6 dB of gain, though as any radio amateur will tell you, always take antenna gain figures with a pinch of salt. It does however provide a significant improvement in range, which for the investment put in you certainly can’t complain at. Give it a try, and bring connectivity back to far-flung corners of your home!

We’ve covered quite a few WiFi Yagis here over the years, such as this rather extreme wardriving tool. But few have been this cheap.

Thanks to London Hackspace Radio Club for the tip.

Pumping Up An Antenna From A Stream Of Sea Water

Our Hackaday readership represent a huge breadth of engineering experience and knowledge, and we get a significant number of our story tips from you. For instance, today we are indebted to [sonofthunderboanerges] for delivering us a tip in the comment stream of one of our posts, detailing an antenna created by coupling RF into a jet of sea water created with a pump. It’s a few years old so we’re presenting it as an object of interest rather than as a news story, but it remains a no less fascinating project for that.

The antenna relies on the conductivity of sea water to view a jet of water as simply another conductor to which RF can be coupled. The jet is simply adjusted by altering the flow rate until it is a quarter wavelength long at the desired frequency, at which point it is a good analogue of a metal whip antenna. The RF is coupled at the base by a ferrite cored transformer that clips around the nozzle ejecting the water, and a bandwidth from 2MHz to 400MHz is claimed. If you work with RF you will probably wince at the sight of salt water coming near the RF connector, as we did.

The advantage of the system is that it allows antennas of multiple frequencies to be created at very short notice and using very little space or weight when not in use. The creator of the antenna at the US Navy’s SPAWAR technology organization points to its obvious application on Navy warships. Whether or not the sailors are using these antennas now isn’t clear, but one thing’s for certain, the idea hasn’t gone away. Early last year Popular Mechanics reported on a similar project under way courtesy of Mitsubishi, in Japan.

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The Poynting Vector Antenna

Radio amateurs are inventive people, and though not all of them choose to follow it there is a healthy culture of buildng radio equipment among them. In particular the field of antennas is where you’ll find a lot of their work, because the barrier to entry can be as low as the cost of a reel of wire.

Over the years a number of innovative antenna designs have come from radio amateurs’ experimentation, and it’s one of the more recent we’d like to share with you today following a [Southgate ARC] story about a book describing its theory (Here’s an Amazon link to the book itself). The Poynting Vector antenna has been one of those novel designs on the fringes for a while now, it has been variously described as the “Super-T”, or the “flute”. Its party piece is tiny dimensions, a fraction of the size of a conventional dipole, and it achieves that by the interaction between a magnetic field across the plates of a capacitor in a tuned circuit and the electric field between a very short pair of dipole radiators. The trade-off is that it has an extremely high Q and thus a narrow bandwidth, and since its feeder can become part of its resonant circuit it is notoriously difficult to match to a transmitter. [Alan MacDonald, VE3TET] and [Paul Birke, VE3PVB] have a detailed page on the development of their Poynting antenna which takes the reader through the details of its theory and the development of their practical version.

In the roof space above the room in which this is being written there hangs a traditional dipole for the 20m amateur band. Though it is a very effective antenna given that it is made from a couple of pieces of wire and a ferrite core it takes most of the length of the space, and as we’re sure Hackaday readers with callsigns will agree a relatively tiny alternative is always very welcome.

If antennas are a mystery to you then we’d suggest you read an introduction to antenna basics to get you started.

Toshiro Kodera: Electromagnetic Gyrotropes

We’ve learned a lot by watching the talks from the Hackaday Superconferences. Still, it’s a rare occurrence to learn something totally new. Microwave engineer, professor, and mad hacker [Toshiro Kodera] gave a talk on some current research that he’s doing: replacing natural magnetic gyrotropic material with engineered metamaterials in order to make two-way beam steering antennas and more.

If you already fully understood that last sentence, you may not learn as much from [Toshiro]’s talk as we did. If you’re at all interested in strange radio-frequency phenomena, neat material properties, or are just curious, don your physics wizard’s hat and watch his presentation. Just below the video, we’ll attempt to give you the Cliff’s Notes.

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RainCube Spreads Its Umbrella

There are times when a mechanism comes to your attention that you have to watch time and time again, to study its intricacies and marvel at the skill of its designer. Sometimes it can be a complex mechanism such as a musical automaton or a mechanical loom, but other times it can be a device whose apparent simplicity hides its underlying cleverness. Such a moment came for us today, and it’s one we have to share with you.

RainCube is a satellite, as its name suggests in the CubeSat form factor and carrying radar instruments to study Earthly precipitation. One of the demands of its radar system is a parabolic dish antenna, and even at its 37.5 GHz  that antenna needs to be significantly larger than its 6U CubeSat chassis.

The unfolding parabola in action.
The unfolding parabola in action.

It is the JPL engineers’ solution to this problem that is the beautiful mechanism we want to show you. The parabola is folded within itself and tightly furled round the feedhorn within the body of the satellite. As the feedhorn emerges, first the inner sections unfurl and then the outer edge of the parabola springs out to form the dish antenna shape. Simultaneously a mechanism of simplicity, cleverness, and beauty, one we’d be very proud of if it were our creation.

There is nothing new in collapsible parabolas used in spacecraft antennas, petal and umbrella-like designs have been a feature of some of the most famous craft. But the way that this one has been fitted into such a small space (and so elegantly) makes it special, we hope you’ll agree.

[via space.com]