Making a software defined radio (SDR) receiver is a relatively straightforward process, given the right radio front end electronics and analogue-to-digital converters. Two separate data streams are generated using clocks at a 90 degree phase shift, and these are passed to the software signal processing for demodulation. But what happens if you lack a pair of radio front ends and a suitable clock generator? Along comes [Mordae] with an SDR using only the hardware on a Raspberry Pi Pico. The result is a fascinating piece of lateral thinking, extracting something from the hardware that it was never designed to do.

The onboard RP2040 ADC is of course far too slow for the task, so instead an input is used, with a negative feedback arrangement from another GPIO to form a crude 1-bit ADC. A PIO peripheral is then used to perform the quadrature mixing, resulting in the requisite pair of data streams. At this point these are sent over USB to GNU Radio for demodulating, mainly for convenience rather than necessarily because the microcontroller lacks the power.

The result is a working SDR front end, demonstrated pulling in an FM broadcast station. The Pico has to be overclocked to reach that frequency and it’s more than a little noisy, but we’re extremely impressed with how much has been done with so little. Oddly it isn’t the first Pico SDR we’ve seen, but the previous one was a much more conventional and lower-frequency affair for the European Long Wave band.

We’ll admit to not fully knowing what [Jay Doscher] has planned for the pair of RTL-SDR Blog V4 software defined radios (SDRs) that are enclosed in the slick 3D printed enclosure he’s designed. But when has that ever stopped us from appreciating a nice design when we see one?

Inside the ventilated enclosure is the aforementioned pair of RTL-SDR Blog V4 (SDRs), as well as a StarTech USB hub that they’re plugged directly into. It seems like it wouldn’t take much to adapt this design to any other pair of USB gadgets, such as flash drives or WiFi adapters.

In fact, if they’re smaller than the RTL-SDR [Jay] has used here, you could probably get away with only needing to modify the one side panel of the case.

The simple modularity of the design, with two end pieces and the top and bottom plates, makes such modifications easy as you don’t need to reprint the whole thing if you just want a different antenna aperture. It also makes it easy to print without support material, and with just a few tweaks, looks like it could be adapted to use laser-cut panels for the sides. This would not only be faster than printing, but depending on the material, could make for a very stout enclosure.

We’ve covered several designs from [Jay] over the years, including a number of heavy-duty mobile “doomsday” computers that certainly fit in with this same design aesthetic. After all, why not face the end of the world with a little style?

Like most waves in the electromagnetic spectrum, radio waves tend to bounce off of various objects. This can be frustrating to anyone trying to use something like a GMRS or LoRa radio in a dense city, for example, but these reflections can also be exploited for productive use as well, most famously by radar. Radar has plenty of applications such as weather forecasting and various military uses. With some software-defined radio tools, it’s also possible to use radar for tracking aircraft in real-time at home like this DIY radar system.

Unlike active radar systems which use a specific radio source to look for reflections, this system is a passive radar system that uses radio waves already present in the environment to track objects. A reference antenna is used to listen to the target frequency, and in this installation, a nine-element Yagi antenna is configured to listen for reflections. The radio waves that each antenna hears are sent through a computer program that compares the two to identify the reflections of the reference radio signal heard by the Yagi.

Even though a system like this doesn’t include any high-powered active elements, it still takes a considerable chunk of computing resources and some skill to identify the data presented by the software. [Nathan] aka [30hours] gives a fairly thorough overview of the system which can even recognize helicopters from other types of aircraft, and also uses the ADS-B monitoring system as a sanity check. Radar can be used to monitor other vehicles as well, like this 24 GHz radar module found in some modern passenger vehicles.