RF Shield Turns Arduino (And PC) Into Shortwave Radio

February 14, 2020 by 10 Comments

Microcontrollers tend to consume other kinds of electronics. A project you might once have done with a 555 now probably has a cheap microcontroller in it. Music synthesizers? RC controllers? Most likely, all microcontroller-based now. We always thought RF electronics would be immune to that, but the last decade or two has proven us wrong. Software-defined radio or SDR means you get the RF signal to digital as soon as possible and do everything else in software. If you want an introduction to SDR, Elektor now has an inexpensive RF shield for the Arduino. The Si5351-based board uses that oscillator IC to shift RF signals down to audio frequencies and then makes it available to the PC to do more processing.

The board is available alone or as part of a kit that includes a book. There’s also a series of Elektor articles about it. There’s also a review video from Elektor about the board in the video, below.

Continue reading “RF Shield Turns Arduino (And PC) Into Shortwave Radio” →

Cache Shortwave Signals For Later With This SDR Spectrum Grabber

November 18, 2016 by 6 Comments

Shortwave listening has always been a mainly nocturnal hobby. To get the real DX, one had to wait for favorable ionospheric conditions after sunset and spend hours twisting knobs while straining to pick voices from half a planet away out of the noise. But who has time for that in today’s world? And what of the poor city-dwelling SWL, with antenna limitations and often elevated noise floor in the urban jungle?
Continue reading “Cache Shortwave Signals For Later With This SDR Spectrum Grabber” →

BST-1 Car Shortwave Receiver

July 24, 2016 by 27 Comments

Commuting is a pain. Luckily, nearly every car has some sort of radio or other audio player to while away the hours stuck in traffic. However, most of those radios sport AM and FM bands, along with a weather band and–maybe–a long wave band. What if you prefer shortwave?

[Thomas] posted a review of the BST-1, a car-friendly shortwave receiver. The device is made to mount out of sight–presumably near an external antenna. It beams the shortwave signal to the car’s FM radio. The control is a small key fob and even if you aren’t interested in the radio itself, the user interface design is somewhat interesting.

Continue reading “BST-1 Car Shortwave Receiver” →

Seeing The Truly Invisible With DIY Shortwave UV Imaging

July 6, 2016 by 19 Comments

We’ve all seen how to peel IR filters off digital cameras so they can see a little better in the dark, but there’s so much more to this next project than that. How about being able to see things normally completely outside the visual spectrum, like hydrogen combustion or electrical discharges?

UV Electrical Discharge

[David Prutchi] has just shared his incredible work on making his own shortwave ultraviolet viewers for imaging entirely outside of the normal visible spectrum – in other words, seeing the truly invisible. The project has not only fascinating application examples, but provides detailed information about how to build two different imagers – complete with exact part numbers and sources.

UV-Viewer-SmallIf you’re thinking UV is a broad brush, you’re right. [David Prutchi] says he is most interested in Solar Blind UV (SBUV):

Solar radiation in the 240 nm to 280 nm range is completely absorbed by the ozone in the atmosphere and cannot reach Earth’s surface…

Without interference from background light, even very weak levels of UV are detectable. This allows ultraviolet-emitting phenomena (e.g. electrical discharges, hydrogen combustion, etc.) to be detectable in full daylight.

There is more to the process than simply slapping a UV filter onto a camera, but happily he addresses all the details and the information is also available as a PDF whitepaper. [David Prutchi] has been working with imaging for a long time, and with his sharing of detailed build plans and exact part numbers maybe others will get in on the fun. He’s also previously shared full build plans for a Raspberry Pi based multispectral imager, [David’s] DOLPHi Polarization Camera was a finalist in the 2015 Hackaday Prize, and he spoke at the Hackaday SuperConference about the usefulness of advanced imaging techniques for things like tissue analysis in medical procedures, and landmine detection for the purposes of cleaning up hazardous areas.

Hacking The R-390A Military Shortwave Radio Receiver To Transmit As Well

June 6, 2013 by 12 Comments

hacking-r390a-radio

After getting his hands on this relic [Gregory Charvat] manage to hack it, converting the receiver into a transceiver.

It may be old, but the R-390A is nothing to scoff at. It’s abilities include AM, code, and FSK operation from 500 kHz to 32 MHz. But it is a receiver with no way of transmitting on the same bands. This is where [Gregory’s] hack comes into play. He rerouted the variable-frequency oscillator feed inside of the R-390A in order to use his 20M single-sideband unit. Basically what this does is allow him to control everything from the 390, using the microphone from the SSB — along with some switching hardware — to transmit his own messages.

His demo video starts with him making a few contacts using the hacked equipment. He then spends some time at the whiteboard explaning the changes. This portion went over our heads, but it becomes more clear when he cracks open the case and shows the actual modifications.

Continue reading “Hacking The R-390A Military Shortwave Radio Receiver To Transmit As Well” →

Spy Tech: The GPS Numbers Station

June 8, 2026 by 24 Comments

We’ve talked before about number stations — mysterious shortwave transmitters repeating numbers, presumably for clandestine purposes. But, of course, the mere fact that they are unusual makes them stand out. The best place to hide something is in plain sight. In the old days, a broadcaster might slip a fake news story in mentioning a name that has a secret meaning, for example. But according to [Steven Murdoch], the United States has an even more obvious hiding place for a numbers station: inside GPS.

Every L1 C/A navigation message is a 176-bit field known by the affectionate moniker: Subframe 4, Page 17. The GPS specification says it is for “special messages.” No one has disclosed what those messages might be.

[Murdoch] at University College London analyzed over 12 million GPS packets from 2007 to 2026, trying to understand what was in this field. You might think 176 bits isn’t much, and you are right. But the L1 C/A signal carries 50 bits per second, and each frame is 1,500 bits. As [Murdoch] points out: “every bit must earn its place.” Each subframe is 300 bits, so this mysterious signal is 12% of the subframe. It must be important to someone.

Continue reading “Spy Tech: The GPS Numbers Station” →

So Long, CHU, And Thanks For All The Time Signals

May 27, 2026 by 60 Comments

In the long ago, pre-internet days when your clock project wasn’t an ESP32 getting its timing via NTP over WiFi, it was still possible to build a wirelessly-updating clock. All you needed was a shortwave receiver tuned to a time signal — perhaps like the National Research Council of Canada’s CHU, found on the dial at 3330, 7850, and 14 670 kHz. At least, it can be found at those frequencies until June 22nd, 2026, when the station will finally go dark.

Depending where you were on Earth, it might have been easier to tune into CHU than the United States based WWVB, or one of the various European signals like DCF77 or the UK’s MSF. If you’re not into radio, all these time signals have essentially the same job, if you hadn’t guessed: tell the time. This can be done in a variety of ways, and CHU has made use of more than one of them since its establishment in 1923.

Initially, the time was sent in Morse code, but later they added a speaking clock for easier human listening in both Canadian French and English. For synchronizing radio clocks, a series of pulses is given in DUT1 format using 0.3s pulses — which is what older clocks would have been listening to — and nowadays a digital FSK time code for more modern equipment. You can have a listen through the video by [Shortwave Listener] embedded below.

It’s not our place to judge the Government of Canada for trying to save money where they can. It wasn’t so long ago that WWVB was in danger of shutting down for similar reasons. But we’re still going to miss those beeps. If you do tune in before the station goes dark, CHU should still be giving out QSL cards. Get yours before it’s gone forever.

If you do have a clock that relies on this time signal, don’t worry. You can make your own, perhaps with a GPS time source.

Continue reading “So Long, CHU, And Thanks For All The Time Signals” →