There are plenty of radios you can buy that pick up MW and SW bands if that’s what you’re into. Or, you can follow [mircemk]’s example, and whip one up yourself instead.
The build employs an ESP32 as the brains of the operation. It’s hooked up to a rotary encoder and a small colour TFT screen, which displays an old-school style tuning dial for choosing the desired frequency. This setup is paired with an Si5351—a capable clock generator chip that can deliver just about any frequency from <8KHz up to 150+ MHz on command. There’s naturally a bunch of supporting analog hardware for the radio end of things, plus a NE612 mixer IC and a PAM8403 class D audio amplifier board, hooked up to a small 0.25W speaker for audio output. [mircemk] has set up the rig to act as a simple radio set, or, with the flick of a switch, it can be configured for SDR use with an attached computer.
It’s a handsome build, and one that likely proves a pleasant way to browse the MW and SW bands on a rainy afternoon. We’ve looked at other hardware in this category before, too. Video after the break.
We’re all used to satellite navigation systems such as GPS or GLONASS, sheer magic in which the combination of a set of reference transmitters and super-accurate timing information can be used to calculate a position to an astounding precision. They had land based predecessors such as LORAN and Decca Navigator which worked in a similar fashion but with fixed land-based reference transmitters. Terra is an attempt to do the same thing without a network of dedicated transmitters, instead using FM broadcast transmitters as its fixed points.
This might seem like an impossible task without access to the transmitters, but they have a workaround using the Internet as a backhaul. Instead of transmitting their timing information like the systems mentioned above, they rely on a set of reference receivers sharing it online to the client’s receiver software. So far they have a demo running in Denver.
The interesting thing about this system is that it’s open-source, and requires only a relatively inexpensive software defined radio receiver and a computer to operate. Now anyone with a group of internet-connected friends to set up reference receivers can have their own positioning system, it’s no longer the exclusive preserve of governments. We like this idea, and we look forward to seeing it being tested more widely.
[Sam Wilkinson] recently installed a Dreo CLF513S ceiling fan in his place — it’s cheap, well-sized, and blows air around as you’d expect it to. The only problem is that it only works with an ugly cloud-only smart home setup out of the box. Never mind, though, because [Sam] figured out how to hack up a custom solution.
Hacking efforts began with the included remote control. [Sam] identified that the remote had to be RF, since it didn’t need line of sight to work properly. The FCC ID on the back of the device further indicated this was the case. Armed with that knowledge, it was simply a case of figuring out the commands sent by the remote, building something to replay them, and then hooking that into [Sam]’s existing Home Assistant setup.
The remote ran on 433.92 MHz, a not-uncommon bit of spectrum for these sort of appliances. An RTL-SDR was thusly enlisted to capture the output, with a spectrogram indicating the remote used simple on-off keying to send commands. Once commands were captured, [Sam] grabbed an ESP32-C6 microcontroller, hooked it up to a RFM69HCW radio transceiver, and programmed it to replay the fan on/off command. From there, a little dabbling with MQTT got the ESP32 controlling the fan as desired from within the Home Assistant ecosystem.
Something happened this morning which will have been unnoticed by many, but which for a certain breed of radio enthusiast marks the end of an era. The BBC stopped broadcasting Radio 4 on their 198 kHz Long Wave frequency, ending over a century of transmission in the band. For now the transmitter carries a recorded message telling listeners that the service has ended, but it’s expected that this will soon be turned off.
The main 198kHz BBC transmitter, at Droitwich. Bob Nienhuis, Public domain.
American readers may be unfamiliar with Long Wave as it’s a band not allocated in their region. Covering 153 to 279 kHz, it’s a relic from the earliest days of high-power broadcasting in the 1920s, used because of the enormous distances that could be covered with its lower frequencies. The main long wave transmitter for the BBC is at Droitwich, and its demise comes because there are no more spares for its high-power transmitter tubes. It joins many Medium Wave, or AM, as it is commonly known, stations in leaving the airwaves, as increased interference from switch mode electronics and the availability of higher quality alternatives took away their listeners. It’s fair to say that there will be few whose lives are inconvenienced by the switch-off in 2026, but it’s worth taking a moment to remember.
The first BBC Long Wave transmissions in the mid-1920s were on a 1600 metre wavelength, or 187.5 kHz. A series of international agreements saw them move to 193 kHz, and then 200 KHz or 1500 metres in 1934. They stayed on that frequency until another shift down 2 KHz to 198 kHz in 1988. They were atomic-controlled, and thus usable as a frequency standard. The programming started with station names redolent of their era, first the BBC National Service, then the Light Programme you’ll see on the dial in the header image, and finally the more modern-sounding Radio 4. A famous BBC programme tied to Long Wave is the Shipping Forecast, a weather bulletin for deep-sea fishermen which became cult listening on land and now features on FM and digital services too, and there’s even a probably-apocryphal tale that British nuclear submarine captains would once use its presence or absence to judge whether nuclear war had occurred.
In an Oxfordshire farmhouse not far short of fifty years ago, a young child who would later become a Hackaday writer heard a radio show like nothing before, which made an impression that continues to this day. The show was one of the earliest airings of the original Hitchhikers Guide To The Galaxy radio series, through a 1970s ITT radio tuned to BBC Radio 4 on (then) 200 kHz Long Wave. So long, Droitwich, and thanks for all the fish.
Although the basic principle of radio direction finding is easy to understand (measure the phase difference between different antennas, then calculate the angle of arrival from this difference), the radio hardware to actually implement this has historically been hard for hackers to access. The QuadRF project aims to change this by building a phase-coherent four-channel SDR which makes direction mapping easy (GitHub repository).
The QuadRF uses two boards: one to receive and pre-process radio waves, and a Raspberry Pi 5 for additional processing. The RF board has four patch antennas, each capable of either transmitting or receiving in the 4.9 GHz to 6.0 GHz range, with switchable right- or left-hand polarization. For on-device processing, it uses a Lattice ECP5 FPGA, which uses two MIPI cables to connect to the camera and display interfaces on the Raspberry Pi. These form a very high-speed data exchange, and after further processing, the Pi can pass data on over Ethernet or Wi-Fi. Individual QuadRF boards can connect together in a lattice grid to form larger phased arrays.
The QuadRF’s software shows off its real strength: it’s compatible with standard programs like GNU Radio, but it also hosts a few of its own programs. The most striking of these is an “RF camera” which scans its entire frequency range at 30 fps, tracking the direction of detected signals and visualizing them on a spatial plot. When overlaid on a camera feed, this plot lets one easily see the radio signals emitted from electronics; as an example, the creators tracked a drone in flight, even distinguishing the two radio transmitters on the drone.
This isn’t the first multi-antenna SDR we’ve seen, though this is the first that could transmit. It’s important to be careful, though: some applications of this kind of hardware run afoul of arms regulations.
What counts as portable is somewhat a matter of opinion, especially over the years. [Helge Fykse] has a portable spy radio of Swedish origin. For its time, it was considered very portable, crammed into a good-sized suitcase.
You can see the large crystal that sets the transmit frequency and a key to send Morse code. The receiver has a VFO, so it was more agile. Based on the regenerative knob, it appears the receiver was of the regenerative type. The suitcase had its own battery, and with tubes, it could probably put out some kind of signal if connected to anything metal, like bedsprings, a clothesline, or anything. There was a lightbulb to let you see when you were transmitting maximum power.
Speaking of tubes, there were five inside, two for the transmitter and three for the receiver. The radio had storage for spare tubes, and the agent could maintain the radio in the field.
You not only get a peek inside the suitcase, but a look at the schematic. The radio is a model of simplicity, but we are certain it did its job.
If you work with radio, the chances are that before too long you’ll be winding an inductor. At radio frequencies these won’t be big chunky transformer style chokes, but often air-cored affairs supported by their own rigidity. As grizzled old radio amateurs will tell you though, relying on such a coil for stability is a fool’s errand. It will shift inductance from the slightest movement, thermal expansion, or even sound. Luckily [SolderSmoke] is here to remind us of the trusty fix, in the form of Q-dope, or a polystyrene solution that dries to form a rigid low-dielectric coating.
Where this is being written it wasn’t on the market so it was more usual to use nail lacquer, but reading the piece it seems American hams swore by the stuff. That’s in the past tense because it seems it’s no longer on the market. Even there though help is at hand, because dissolving packaging polystyrene in solvent yields an acceptable substitute. There’s even an 11-year-old how-to video linked from the SolderSmoke post, should you fancy making some of your own. We suggest you proceed with caution though, polymers dissolved in solvents sounds a lot like home-made napalm, and probably puts out fumes you don’t want to breathe.
Meanwhile should you fancy experiments of your own with inductors, we’ve got you covered.
