A Very 21st Century Receiver For A Very 20th Century Band

January 9, 2024 by Jenny List 24 Comments

The FM broadcast band has been with us since the middle of the 20th century, and despite many tries to unseat it, remains a decent quality way to pick up your local stations. It used to be that building an FM broadcast receiver required a bit of RF know-how, but the arrival of all-in-one receiver chips has made that part a simple enough case of including a part. That’s not to say that building a good quality FM broadcast receiver in 2024 doesn’t involve some kind of challenge though, and it’s one that [Stefan Wagner] has risen to admirably with his little unit.

Doing the RF part is an RDA5807MP single chip radio, but we’d say the center of this is the CH32V003 RISC-V microcontroller and its software. Twiddling the dial is a thing of the past, with a color display and all the computerized features you’d expect. Rounding it off in the 3D printed case is a small speaker and a Li-Po pouch cell with associated circuitry. This really is the equal of any commercially produced portable radio, and better than many.

Even with the all-in-one chips, there’s still fun in experimenting with FM the old way.

Discovery Dish Lets You Pick Up The Final Frontier

January 7, 2024 by Tom Nardi 15 Comments

These days, affordable software defined radios (SDRs) have made huge swaths of the spectrum available to hobbyists. Whether you’re looking to sniff the data from that 433 MHz thermometer you’ve got in the backyard or pick up transmissions from satellites, the same little USB-connected box can make it happen.

But even the best SDR is constrained by the antenna it’s connected to, and that’s where it can still get a little tricky for new players. Luckily, there’s a new option for those who want to pick up signals from space without breaking the bank: the Discovery Dish by KrakenRF. After reaching 105% of its funding goal on December 20th, the handy little 65-cm aluminum reflector looks like it’s on track to ship out this summer.

The Discovery Dish was designed from the ground up to enable hobbyists to receive real-time weather data from satellites transmitting in the L band (GOES, NOAA, Meteor, etc.) and experiment with hydrogen line radio astronomy. Neither of which are anything new, of course. But having a pre-built dish and feed takes a lot of the hassle out of picking up these distant signals.

Although the current prototype has a one-piece reflector, the final Discovery Dish will break down into three “petals” to make storage and transport easier. If you don’t want to take it all the way apart, you can simply remove the feed to make it a bit more compact. Speaking of which, KrakenRF is also offering three different feeds depending on what signals you’re after: L band, Inmarsat, or hydrogen line.

You still have options if you’ve got to keep your radio hacking on a tighter budget. As we saw recently, you can actually pull an ET and pick up weather satellites using a foil-lined umbrella. Or spend a little at the big box hardware store and grab some aluminum flashing.

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A microwave imaging setup. On the left is a monitor displaying a monochrome GUI. In the center is the RP2040-based positioning and measurement system, and on the right is a vector network analyzer.

Precise Positioning With The RP2040

January 1, 2024 by Stephen Ogier 10 Comments

Microwave imaging is similar to CT imaging, but instead of X-rays, the microwaves are used to probe the structure and composition of an object. To facilitate experimentation with microwave imaging, [Zehao Li] and [Kapil Gangwar] developed a system based on the RP2040 to control the height and rotation of a test object.

Their control system has a refreshingly physical user interface—a keypad. The keypad is used to configure the object’s position and the scanning step size, while user menus and the sample position are displayed in a clean and uncluttered interface over VGA. The RP2040 runs a multi-threaded program to handle user input, VGA display, and precise driving of two stepper motors for sample positioning.

The microwave imaging was performed by measuring the RF transmission over 2.5-8 GHz between two Vivaldi antennas on either side of the sample at a variety of angles. 2D cross-sections of the test object were reconstructed in Matlab using filtered back-projection. In this proof-of-concept demonstration, a commercial vector network analyzer was used to collect the data, but one could imagine migrating to a software defined radio (SDR) in the future.

A video demonstrating the system is embedded below the break. If you’re interested in DIY radio imaging, you might be interested in this guide to building your own synthetic aperture radar setup, or this analysis of an automotive radar chip.

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Radiochat Is A Simple LoRa Interface Over WiFi

December 25, 2023 by Lewin Day 20 Comments

LoRa is often talked about as a potentially useful solution for emergency communication. The problem is, few of us are running around with LoRa hardware on a day-to-day basis. Student [William Barkoff] designed the Radiochat device as a simple tool that could pair with virtually anything over WiFi, and allow it to send and receive LoRa messages.

Radiochat is based on the Raspberry Pi Pico W, and uses the microcontroller’s wireless hardware to communicate with other devices. It provides a WiFi network that devices like laptops or smartphones can connect to. The Pico serves up a simple web page which accepts text input. Type in a message and hitting enter and the Pico will command a LoRa radio module over SPI to send that message out over the airwaves. It can then be picked up by another Radiochat module which displays the message on its own webpage.

It’s in an early state of development, and the demo video shows there are still some bugs to work out. Ultimately, though, it could be a cheap battery-powered device that lets smartphones and laptops chat over LoRa in remote areas. Indeed, [William’s] trips to New Mexico on model rocketry expeditions were a big inspiration for the project.

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Roll Your Own SDR

December 16, 2023 by Al Williams 8 Comments

If you have software-defined radio hardware and you are only using someone elses’ software, you are missing out on half of the fun. [Tech Minds] shows you how easy it can be to roll your own software using GNU Radio Companion in a recent video.

GNU Radio usually uses Python, but with the companion software you rarely need to know any actual Python. Instead, you simply drag blocks around to represent filters, DSP processing, and other functions you need to create the processing for your application.

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The Trans-Harmonium Is A Strange Kind Of Radio-Musical Instrument

December 13, 2023 by Lewin Day 17 Comments

Pianos use little hammers striking taut strings to make tones. The Mellotron used lots of individual tape mechanisms. Meanwhile, the Trans-Harmonium from [Emily Francisco] uses an altogether more curious method of generating sound — each key on this keyboard instrument turns on a functional clock radio.

Electrically, there’s not a whole lot going on. The clock radios have their speaker lines cut, which are then rejoined by pressing their relevant key on the keyboard. As per [Emily]’s instructions for displaying the piece, it’s intended that the radio corresponding to C be tuned in to a local classical station. Keys A, B, D, E, F, and G are then to be tuned to other local stations, while the sharps and flats are to be tuned to the spaces in between, providing a dodgy mix of static and almost-there music and conversation.

It’s an interesting art piece that, no matter how well you play it, will probably not net you a Grammy Award. That would be missing the point, though, as it’s more a piece about “Collecting Fragments of Time,” a broader art project of which this piece is a part.

We do love a good art piece, especially those that repurpose old hardware to great aesthetic achievement.

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Modern Spark Gap Transmitter Uses A Rotary Gap

December 11, 2023 by Al Williams 18 Comments

In the “don’t try this at home” category, [Joe Smith] builds a spark gap transmitter with a twist. The twist is that the drive power is from a signal generator attached to a FET. From there, though, things go classic using an automotive ignition coil and a tank circuit. He shows how adjusting the spark frequency changes the signal’s sound in a standard receiver.

We say don’t try this at home because the output of a transmitter like this will likely spew RF all over the place. Granted, there’s probably not much power, but it may well irritate your neighbors.

Switching to AM, you can really hear the tone from the spark frequency in the receiver. [Joe] posted some earlier videos where he made a 160-meter spark gap transmitter using an electric fly swatter. There are more details about how the tank circuits work in those videos. You can also see what the output looks like on a spectrum analyzer. You can hear what that transmitter sounds like, too.

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