[Eric] Talks Crystal Radios

January 28, 2020 by Al Williams 42 Comments

The AM broadcast band doesn’t have a lot of mainstream programming on it across much of the United States today. That’s a shame because a lot of kids got their first taste of radio and electronics by building simple crystal radios. [Eric Wrobbel] has a well-done page discussing some of the crystal radio kits and toys that have been around.

[Eric] should know, as he’s written two books on toy crystal radios. The pictures range from a 1945-era “Easy Built Radio Kit” which looks like a piece of masonite with a coil, some Fahnestock clips, and a cat whisker, to a very slick looking Tinymite from 1949. Honestly, though, the one we really want is the X-50 Space Helmet Radio that comes in a box marked “For Young Moon Travelers.”

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RF Modulation: Crash Course For Hackers

January 28, 2020 by Danie Conradie 16 Comments

When you’re looking to add some wireless functionality to a project, there are no shortage of options. You really don’t need to know much of the technical details to make use of the more well-documented modules, especially if you just need to get something working quickly. On the other hand, maybe you’ve gotten to the point where you want to know how these things actually work, or maybe you’re curious about that cheap RF module on AliExpress. Especially in the frequency bands below 1 GHz, you might find yourself interfacing with a module at really low level, where you might be tuning modulation parameters. The following overview should give you enough of an understanding about the basics of RF modulation to select the appropriate hardware for your next project.

Three of the most common digital modulation schemes you’ll see in specifications are Frequency Shift Keying (FSK), Amplitude Shift Keying (ASK), and LoRa (Long Range). To wrap my mechanically inclined brain around some concepts, I found that thinking of RF modulation in terms of pitches produced by a musical instrument made it more intuitive.

And lots of pretty graphs don’t hurt either. Signals from two different RF dev boards were captured and turned into waterfall and FFT plots using a $20 RTL-SDR dongle. Although not needed for wireless experimentation, the RTL-SDR is an extremely handy debugging tool, even to just check if a module is actually transmitting. Continue reading “RF Modulation: Crash Course For Hackers” →

A Simple Science Fair AM Transmitter

January 23, 2020 by Al Williams 18 Comments

A crystal radio is a common enough science fair project, but the problem is, there isn’t much on anymore. The answer is, of course, obvious: build your own AM transmitter, too. AM modulation isn’t that hard to do and [Science Buddies] has plans for how to build one with a canned oscillator and an audio transformer.

We don’t imagine the quality of this would be so good, but for a kid’s science project it might be worth a shot. Maybe something like “What kind of materials block radio waves?” would be a good project statement.

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The RFI Hunter: Looking For Noise In All The Wrong Places

January 15, 2020 by Dan Maloney 22 Comments

Next time you get a new device and excitedly unwrap its little poly-wrapped power supply, remember this: for every switch-mode power supply you plug in, an amateur radio operator sheds a tear. A noisy, broadband, harmonic-laden tear.

The degree to which this fact disturbs you very much depends upon which side of the mic you’re on, but radio-frequency interference, or RFI, is something we should all at least be aware of. [Josh (KI6NAZ)] is keenly aware of RFI in his ham shack, but rather than curse the ever-rising noise floor he’s come up with some helpful tips for hunting down and eliminating it – or at least reducing its impact.

Attacking the problem begins with locating the sources of RFI, for which [Josh] used the classic “one-circuit-at-a-time” approach – kill every breaker in the panel and monitor the noise floor while flipping each breaker back on. This should at least give you a rough idea of where the offending devices are in your house. From there, [Josh] used a small shortwave receiver to locate problem areas, like the refrigerator, the clothes dryer, and his shack PC. The family flat-screen TV proved to be quite noisy too. Remediation techniques include wrapping every power cord and cable around toroids or clamping ferrite cores around them, both on the offending devices and in the shack. He even went so far as to add a line filter to the dryer to clamp down on its unwanted interference.

Judging by his waterfall displays, [Josh]’s efforts paid off, bringing his noise floor down from S5 to S1 or so. It’s too bad he had to take matters into his own hands – it’s not like the FCC and other spectrum watchdogs don’t know there’s a problem, after all.

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Hiking Pole Turned Lightweight Yagi Antenna

January 9, 2020 by Tom Nardi 10 Comments

Among amateur radio enthusiasts, there’s a subset of users who climb mountainous areas to use their gear from elevated positions. Anyone looking to take part in what’s known as Summits on the Air (SOTA) will obviously want to keep their equipment as light and small as possible. For [Stuart Thomas], that meant a collapsible yagi antenna he could easily pack away.

But one day he wondered why he was carrying around a separate antenna boom when his aluminum hiking pole would make a perfectly good substitute. All he had to do was figure out a way to mount the elements to the pole in a way that could be easily assembled in the field. He initially tried to use the sort of insulated electrical clamps used to hold down conduit, but he found they weren’t quite what he was after.

[Stuart] eventually ended up designing and 3D printing his own element mounts that use an M3 bolt to tightly clamp onto the hiking pole, preventing them from twisting while still being very lightweight and easy to adjust. To further reduce the packed size of the antenna, he cut each element in half with a pipe cutter and flared the ends slightly so he could reassemble them on location with inserts.

Even if you aren’t the type of person who owns hiking poles, let alone climbs mountains for fun, there’s still plenty of interesting applications for a lightweight yagi antenna. We’ve seen custom yagis built out of carbon fiber before and of course cobbling one together out of PVC and tape measures is a classic hack, but we think the solution [Stuart] has come up with strikes a nice balance between the extremes.

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LuaRadio Gives Insight Into SDR

December 24, 2019 by Al Williams 3 Comments

In theory, you shouldn’t need any help to develop a software-defined radio (SDR) application. But in real life you really don’t want to roll your own code every time to read the IQ samples, perform various transformations on them, and then drive audio output. At worst, you’ll use some libraries (perhaps GNU Radio) but usually, you’ll use some higher-level construct such as GNU Radio Companion (GRC). GRC is a bit heavyweight, though, so if you’ve found it daunting before, you might check out some of the material on the LuaRadio website.

We’ve looked at LuaRadio several years ago, but it has undergone a lot of changes since then and has some excellent documentation. Like Lua itself, LuaRadio emphasizes fast scripting. It supports quite a few pieces of common hardware and nearly anything that feeds data through a soundcard.

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All Your SDR Software In A Handy Raspberry Pi Image

December 20, 2019 by Jenny List 29 Comments

The SDR revolution has brought a bonanza of opportunities for experimentation to the radio enthusiast, but with it has come a sometimes-confusing array of software for which even installation can be a difficult prospect for an SDR novice. If you’re bamboozled by it all then help may be at hand courtesy of [Luigi Cruz], who has packaged a suite of ready-to-go popular SDR software in an OS image for the Raspberry Pi.

On board the Raspbian-based OS image are SDR Angel, Soapy Remote, GQRX, GNURadio, LimeUtil, and LimeVNA. In hardware terms the RTL-SDR is supported, along with the LimeSDR, PlutoSDR, Airspy, and Airspy HF. All are completely ready-to-go and even have desktop shortcuts, so if the CLI scares you then you can still dive in and play. More importantly it’s designed for use with SDR transmitters as well as receivers, so the barrier for full SDR operation for radio amateurs has become significantly lower too.

This year has seen the seven-year anniversary of the RTL-SDR hack that probably did most to kickstart the use of SDRs in our community. Our colleague [Tom Nardi] wrote a retrospective that’s worth a look for its overview of some SDR tricks that have evolved over that time. Meanwhile if you don’t mind restricting your outlook somewhat, it’s possible to turn the Raspberry Pi 3 into an SDR all without any extra hardware.