Loop Antenna is Portable

We don’t know if [OH8STN] has a military background, but we suspect he might since his recent post is about a “DIY Man Portable Magnetic Loop Antenna.” “Man-portable” is usually a military designation, and — we presume — he wouldn’t object to a woman transporting it either.

[OH8STN] started with a Chameleon antenna starter kit. This costs about $100 and is primarily a suitable variable capacitor with a 6:1 reduction drive premounted and soldered. Of course, you could source your own, but finding variable capacitors that can handle transmit duty (admittedly, these can apparently handle about 10 W continuous or 25 W on single sideband) can be tricky, especially these days. Although he started with a kit, he did modify the antenna to switch between two different sets of ham radio bands. You can see the antenna in the video below.

Loop antennas aren’t ideal–but neither is any other small antenna. Because the loop is tightly tuned to a particular frequency, it requires retuning for even relatively small frequency changes, even though it can operate on many different frequencies. If you want more technical details, you might enjoy this recent presentation from [W4RAX]. The links at the end are worth checking out, too.

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A Lightweight Two Metre Carbon Fibre Yagi Antenna

If you’ve ever cast your eye towards the rooftops, you’ll be familiar with the Yagi antenna. A dipole radiator with a reflector and a series of passive director elements in front of it, you’ll find them in all fields of radio including in a lot of cases the TV antenna on your rooftop.

In the world of amateur radio they are used extensively, both in fixed and portable situations. One of their most portable uses comes from the amateur satellite community, who at the most basic level use handheld Yagi antennas to manually track passing satellites. As you can imagine, holding up an antenna for the pass of a satellite can be a test for your muscles, so a lot of effort has gone into making Yagis for this application that are as lightweight as possible.

[Tysonpower] has a contribution to the world of lightweight Yagis, he’s taken a conventional design with a PVC boom and updated it with a stronger and lighter boom made from carbon fibre composite pipe. The elements are copper-coated steel welding rods, some inexpensive aluminium clamps came from AliExpress, and all is held together by some 3D-printed parts. As a result the whole unit comes in at a claimed bargain price of under 20 Euros.

This antenna is for the 2 M (144 MHz) amateur band, but since it’s based on the [WB0CMT] “7 dB for 7 bucks”  (PDF) design it should be easily modified for other frequencies. The 3D printed parts can be found on Thingiverse,  and he’s also posted a couple of videos in German. We’ve posted the one showing the build below the break, you can find the other showing the antenna being tested at the link above.

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Hackaday Links: February 5, 2017

A lot of people around here got their start in electronics with guitar pedals. This means soldering crappy old transistors to crappy old diodes and fawning over your tonez, d00d.  Prototyping guitar pedals isn’t easy, though, and now there’s a CrowdSupply project to make it easier The FX Development Board is just that — a few 1/4″ jacks, knobs, pots, power supply, and a gigantic footswitch to make prototyping guitar pedals and other musical paraphernalia easy. Think of it as a much more feature-packed Beavis Board that’s still significantly cheaper.

How do Communicators in Star Trek work? Nobody knows. Why don’t the crew always have to tap their badge before using it? Nobody knows. How can the com badge hear, ‘Geordi to Worf’, and have Worf instantly respond? Oh, we’ve argued about this on IRC for years now. Over on Hackaday.io, [Joe] is building a Star Trek com badge. The electronics are certainly possible with modern microcontrollers, but for the enclosure, we’ll have to review a few scenes from Time’s Arrow and The Enemy.

[Alois] was working with an Intel Edison on a breadboard. He was generating a signal, and sending it through a little tiny breadboard wire to an oscilloscope. The expected waveform should have been a nice square wave at 440MHz. What he got out of this wire was a mess. You shouldn’t use long wires when probing circuits. That little breadboard wire was a perfect radiator for 440MHz, and the entire setup turned into an antenna.

[Douglas] is running a Kenwood TM-D710A as his amateur radio rig. This radio does APRS stuff, but it requires an external GPS and power source to do it right. GPS receivers are now very small and very cheap, so [Douglas] just stuffed a GPS module inside his radio. The module itself is a GP-20U7, a tiny GPS module the size of a postage stamp, and wired it up to a few pads on the radio PCB.

Here’s an upcoming Kickstarter that’s going straight to the front page of Boing Boing. It’s Pong, in coffee table format which we first saw last Spring. Instead of racing the beam, this version of Pong is mechanical. The ball is a cube, the paddles are slightly longer cubes, and the entire game is a highly refined CNC machine. Here’s something from seven years ago that’s also Pong in coffee table format. Pongmechanik is electromechanical Pong, built entirely out of switches, relays, and a few motors.

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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