What Makes A Good Antenna?

January 24, 2021 by Jenny List 13 Comments

It sometimes seems as though antennas and RF design are portrayed as something of a Black Art, the exclusive preserve of an initiated group of RF mystics and beyond the reach of mere mortals. In fact though they have their difficult moments it’s possible to gain an understanding of the topic, and making that start is the subject of a video from [Andreas Spiess]. Entitled “How To Build A Good Antenna”, it uses the design and set-up of a simple quarter-wave groundplane antenna as a handle to introduce the viewer to the key topics.

What makes this video a good one is its focus on the practical rather than the theoretical. We get advice on connectors and antenna materials, and we’re introduced to the maths through online calculators rather than extensive formulae. Of course the full calculations are there to be learned by those with an interest, but for many constructors they can be somewhat daunting. We’re shown a NanoVNA as a useful tool in the antenna builder’s arsenal, one which gives a revolutionary window on performance compared to the trial-and-error of previous times. Even the ground plane gets the treatment, with its effect on impedance and gain explored and the emergence of its angle as a crucial factor in performance. We think this approach does an effective job of breaking the mystique surrounding antennas, and we hope it will encourage viewers to experiment further.

If your appetite has been whetted, how about taking a look at a Nano VNA in action?

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Meet The Magic Eye Vacuum Tube

January 22, 2021 by Al Williams 61 Comments

Vacuum tubes ruled electronics for several decades and while you might think of them as simple devices analogous to a transistor or FET, there were many special types. We’re all familiar with nixie tubes that act as numeric displays, and there are other specialty tubes that work as a photomultiplier, to detect radiation, or even generate microwaves. But one of the most peculiar and distinctive specialty tubes has an intriguing name: a magic eye tube. When viewed from the top, you see a visual indication that rotates around a central point, the out ring glowing while the inner is dark, like an iris and pupil.

These tubes date back to the RCA 6E5 in 1935. At the time, test equipment that used needles was expensive to make, so there was always a push to replace them with something cheaper. They were something like a stunted cathode ray tube. In fact, the inventor, Allen DuMont, was well known for innovations in television. An anode held a coating that would glow when hit with electrons — usually green, but sometimes other colors. Later tubes would show a stripe going up and down the tube instead of a circle, but you still call them magic eyes.

The indicator part of this virtual meter took the form of a shadow. Based on the applied signal, the shadow would be larger or smaller. Many tubes also contained a triode which would drive the tube from a signal.

There’s a great web site full of information on these venerable tubes and it has examples of these tubes appearing in plenty of things. They frequently appeared in service equipment, radios, and tape recorders. They even appeared in pro audio equipment like the Binson Echorec echo-delay unit.

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Fixing NRF24L01+ Modules Without Going (Too) Insane

January 22, 2021 by Donald Papp 24 Comments

Good old nRF24L01+ wireless modules are inexpensive and effective. Well, they are as long as they work correctly, anyway. The devices themselves are mature and well-understood, but that doesn’t mean bad batches from suppliers can’t cause hair-pulling problems straight from the factory.

[nekromant] recently got a whole batch of units that simply refused to perform as they should, but not because they were counterfeits. The problem was that the antenna and PCB design had been “optimized” by the supplier to the point where the devices simply couldn’t work properly. Fortunately, [nekromant] leveraged an understanding of the problem into a way to fix them without going insane in the process. The test setup is shown in the image above, and the process is explained below. Continue reading “Fixing NRF24L01+ Modules Without Going (Too) Insane” →

A Few Of My Favorite Things: Amateur Radio

January 21, 2021 by Jenny List 50 Comments

Hackaday has among its staff a significant number of writers who also hold amateur radio licenses. We’re hardware folks at heart, so we like our radios homebrew, and we’re never happier than when we’re working at high frequencies.

Amateur radio is a multi-faceted hobby, there’s just so much that’s incredibly interesting about it. It’s a shame then that as a community we sometimes get bogged down with negativity when debating the minutia. So today let’s talk about a few of my favourite things about the hobby of amateur radio. I hope that you’ll find them interesting and entertaining, and in turn share your own favorite things in the comments below.

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A One-Transistor Ham Transmitter Anyone Can Build

January 20, 2021 by Dan Maloney 66 Comments

What attracts a lot of people to amateur radio is that it gives you the ability to make your own gear. Scratch-building hams usually start by making their own antennas, but eventually, the itch to build one’s own radio must be scratched. And building this one-transistor transmitter is just about the simplest way to dive into the world of DIY radio.

Of course, limiting yourself to eight components in total entails making some sacrifices, and [Kostas (SV3ORA)]’s transmitter is clearly a study in compromise. For starters, it’s only a transmitter, so you’ll need to make other arrangements to have a meaningful conversation. You’ll also have to learn Morse code because the minimalist build only supports continuous-wave (CW) mode, although it can be modified for amplitude modulation (AM) voice work.

The circuit is flexible enough that almost any part can be substituted and the transmitter will still work. Most of the parts are junk-bin items, although the main transformer is something you’ll have to wind by hand. As described, the transformer not only provides feedback to the transistor oscillator, but also has a winding that powers an incandescent pilot lamp, and provides taps for attaching antennas of different impedances — no external tuner needed. [SV3ORA] provides detailed transformer-winding instructions and shows the final build, which looks very professional and tidy. The video below shows the rig in action with a separate receiver providing sidetone; there’s also the option of using one of the WebSDR receivers sprinkled around the globe to verify you’re getting out.

This little transmitter looks like a ton of fun to build, and we may just try it for our $50 Ham series if we can find all the parts. Honestly, the hardest to come by might be the variable capacitor, but there are ways around that too.

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Remoticon Video: Learning The Basics Of Software-Defined Radio (SDR)

January 19, 2021 by Mike Szczys 8 Comments

Have you dipped your toe into the SDR ocean? While hacker software-defined radio has been a hot topic for years now, it can be a little daunting to try it out for the first time. Here’s your change to get your legs under you with the SDR overview workshop presented by Josh Conway during the 2020 Hackaday Remoticon.

Josh’s presentation starts with a straightforward definition of SDR before moving to an overview of the hardware and software that’s out there. Hardware designs for radios can be quite simple to build, but they’ll be limited to a single protocol — for instance, an FM radio can’t listen in on 433 Mhz wireless doorbell. SDR breaks out of that by moving to a piece of radio hardware that can be reconfigured to work with protocols merely by making changes to the software that controls it. This makes the radio hardware more expensive, but also means you can listen (and sometimes transmit) to a wide range of devices like that wireless doorbell or automotive tire pressure sensors, but also radio-based infrastructure like airplane transponders and weather satellites.

This is the quickstart you want since it explains a lot of topis at just the right depth. The hardware overview covers RTL-SDR, ADALM-PLUTO, HackRF, KerberosSDR, and BladeRF (which we just featured over the weekend used on the WiFi procotol). For software, Josh recaps GQRX, SDR#, SDRAngel, ShinySDR, Universal Radio Hacker, Inspectrum, SigDigger, RPITX, GnuRadio Companion, and REDHAWK. He also takes us through a wide swath of the antenna types that are out there before turning to questions from the workshop attendees.

If SDR is still absent in your toolbox, now’s a great time to give it another look. Once you’ve made it through the ‘hello world’ stage, there’s plenty to explore like those awesome RF Emissions testing tricks we as in another Remoticon talk.

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The $50 Ham: A Cheap Antenna For The HF Bands

January 19, 2021 by Dan Maloney 65 Comments

So far in the $50 Ham series, I’ve concentrated mainly on the VHF and UHF bands. The reason for this has to do mainly with FCC rules, which largely restrict Technician-level licensees to those bands. But there’s a financial component to it, too; high-frequency (HF) band privileges come both at the price of learning enough about radio to pass the General license test, as well as the need for gear that can be orders of magnitude more expensive than a $30 handy-talkie radio.

But while HF gear can be expensive, not everything needed to get on the air has to be so. And since it’s often the antenna that makes or breaks an amateur radio operator’s ability to make contacts, we’ll look at a simple but versatile antenna design that can be adapted to support everything from a big, powerful base station to portable QRP (low-power) activations in the field: the end-fed half-wave antenna.

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