Radio Hacks

1380 Articles

Homebrew Radio Telescope Bags Pulsar

May 25, 2022 by 11 Comments

When one mulls the possibility of detecting pulsars, to the degree that one does, thoughts turn to large dish antennas and rack upon rack of sensitive receivers, filters, and digital signal processors. But there’s more than one way to catch the regular radio bursts from these celestial beacons, and if you know what you’re doing, a small satellite dish and an RTL-SDR dongle will suffice.

Granted, [Job Geheniau] has had a lot of experience exploring the radio universe. His website has a long list of observations and accomplishments achieved using his “JRT”, or “Job’s Radio Telescope.” The instrument looks like a homebrewer’s dream, with a 1.9-m satellite TV dish and precision azimuth-elevation rotator. Behind the feedhorn are a pair of low-noise amplifiers and bandpass filters to massage the 1,420 MHz signal that’s commonly used for radio astronomy, plus a Nooelec Smart SDR dongle and an Airspy Mini. Everything is run via remote control, as the interference is much lower with the antenna situated at his family’s farm, 50 km distant from his home in The Hague.

As for the pulsar, bloodlessly named PSR B0329+54, it’s a 5-million-year-old neutron star located in the constellation of Camelopardalis, about 3,500 light-years away. It’s a well-characterized pulsar and pulses at a regular 0.71452 seconds, but it’s generally observed with much, much larger antennas. [Job]’s write-up of the observation contains a lot of detail on the methods and software he used, and while the data is far from clear to the casual observer, it sure seems like he bagged it.

We’ve seen quite a few DIY radio astronomy projects before, both large and small, but this one really impresses with what it accomplished.

[via RTL-SDR.com]

VR Spectrum Analyzer

May 21, 2022 by 5 Comments

At one point or another, we’ve probably all wished we had a VR headset that would allow us to fly around our designs. While not quite the same, thing, [manahiyo831] has something that might even be better: a VR spectrum analyzer. You can get an idea of what it looks like in the video below, although that is actually from an earlier version.

The video shows a remote PC using an RTL dongle to pick up signals. The newer version runs on the Quest 2 headset, so you can simply attach the dongle to the headset. Sure, you’d look like a space cadet with this on, but — honestly — if you are willing to be seen in the headset, it isn’t that much more hardware.

What we’d really like to see, though, is a directional antenna so you could see the signals in the direction you were looking. Now that would be something. As it is, this is undeniably cool, but we aren’t sure what its real utility is.

What other VR test gear would you like to see? A Tron-like logic analyzer? A function generator that lets you draw waveforms in the air? A headset oscilloscope? Or maybe just a giant workbench in VR?

A spectrum analyzer is a natural project for an SDR. Or things that have SDRs in them.

Continue reading “VR Spectrum Analyzer” →

A Receive Antenna Switcher With An Espressif Brain

May 21, 2022 by 9 Comments

It’s not uncommon for a radio enthusiast to have multiple antennas for the same radio, so as you might expect it’s also entirely usual to have a bunch of coaxial cables dangling down for fumbling around the back of the rig to swap over.  If that describes your radio experience than you might be interested in the antenna switcher built by [g3gg0], which uses solid-state RF switches controlled by an ESP32 module.

At its heart is the MXD8625C RF switch, a tiny device designed for cellular phone applications that delivers only a fraction of a dB insertion loss and somehow negates the need for any blocking capacitors. It’s controlled by a GPIO line, and he’s hooked up a brace of them to allow the distribution of three antennas to a couple of radios with the handy option of switching in a preamplifier if required. Of even more interest we note that the device is suitable for transmitter switching too, with a maximum 36.5 dBm throughput that we calculate to be about 4.5 W. This board is fairly obviously for receive use, but perhaps the chip is of interest to anyone considering a transceiver project. Meanwhile the software is a relatively simple web-based control linking on-screen controls to GPIOs.

If you are interested in solid state RF switches, it’s always worth remembering that at lower frequencies they can be very simple indeed.

When Hams Helped Polar Researchers Come In From The Cold

May 17, 2022 by 26 Comments

We always enjoy [The History Guy] videos, although many of them aren’t much about technology. However, when he does cover tech topics, he does it well and his recent video on how ham radio operators assisted in operation Deep Freeze is a great example. You can watch the video, below.

The backdrop is the International Geophysical Year (IGY) where many nations cooperated to learn more about the Earth. In particular, from 1957 to 1958 there was a push to learn more about the last unexplored corner of our planet: Antarctica. Several of the permanent bases on the icy continent today were started during the IGY.

It’s hard for modern audiences to appreciate what the state of personal communication was in 1957. There were no cell phones and if you are thinking about satellites, don’t forget that Sputnik didn’t launch until late 1957, so that wasn’t going to happen, either.

Operation Deep Freeze had ten U. S. Navy vessels that brought scientists, planes, and Seabees (slang for members of the Naval Construction Batallion) — about 1,800 people in all over several years culminating in the IGY. Of course, the Navy had radio capabilities, but it wasn’t like the Navy to let you just call home to chat. Not to mention, a little more than 100 people were left for each winter and the Navy ships went home. That’s where ham radio operators came in.

Hams would do what is called a phone patch for the people stationed in Antarctica. Some hams also send radiograms to and from the crew’s families. One teen named Jules was especially dedicated to making connections to Antarctica. We can’t verify it, but one commenter says that Jules was so instrumental in connecting his father in Antarctica to his fiancee that when his parents married, Jules was their best man.

Jules and his brother dedicated themselves to keeping a morale pipeline from New Jersey to the frozen stations. He figures prominently in recollections of many of the written accounts from people who wintered at the nascent bases. Apparently, many of the men even traveled to New Jersey later to visit Jules. What happened to him? Watch the end of the video and you’ll find out.

While being a ham today doesn’t offer this kind of excitement, hams still contribute to science. Want to get in on the action? [Dan Maloney] can tell you how to get started on the cheap.

Continue reading “When Hams Helped Polar Researchers Come In From The Cold” →

Hacking Toy RC Cars With The HackRF One

April 30, 2022 by 3 Comments

The origin story for many who’d call themselves a member of the hacker community usually starts with taking things apart as a child just to see how they worked. For [Radoslav], that trend doesn’t seem to have slowed down, and he’s continued taking toys apart. Although since it’s his daughters little radio controlled car, he stuck to a non-destructive teardown. The result? He’s able to control the car with his laptop through a HackRF One SDR transceiver as shown in the video below the break.

[Radoslav] is no stranger to reverse engineering embedded devices, IoT gadgets, and probably more. So he started with what information was publicly available about the radio control interface in use. Many electronic devices sold in the US must be certified by the FCC (Federal Communications Commission) and prominently display their ID number, and this toy was no exception. The FCC database gave [Radoslav] enough information to know that the communication protocol is modulated with GFSK, a type of Frequency Shift Keying.

He fired up his favorite radio signal analysis tool and and got to work on the protocol itself. Along the way he found that communication between the car and controller is bidirectional but also very easy to get around. The result is that he can drive the car around with his laptop- definitely a cool hack, but for this one, the journey was surely the goal, not the destination.

If hacking on RC cars really gets your wheels turning, you might like this little RC car that can drive on the ceiling. Or if you’re feeling a bit hungry, check out how you can use the HackRF to nab a table at your local restaurant.

Continue reading “Hacking Toy RC Cars With The HackRF One” →

Multiband Crystal Radio Set Pulls Out All The Stops

April 28, 2022 by 23 Comments

Most crystal radio receivers have a decidedly “field expedient” look to them. Fashioned as they often are from a few turns of wire around an oatmeal container and a safety pin scratching the surface of a razor blade, the whole assembly often does a great impersonation of a pile of trash whose appearance gives little hope of actually working. And yet work they do, usually, pulling radio signals out of thin air as if by magic.

Not all crystal sets take this slapdash approach, of course, and some, like this homebrew multiband crystal receiver, aim for a feature set and fit and finish that goes way beyond the norm. The “Husky” crystal set, as it’s called by its creator [alvenh], looks like it fell through a time warp right from the 1920s. The electronics are based on the Australian “Mystery Set” circuit, with modifications to make the receiver tunable over multiple bands. Rather than the traditional galena crystal and cat’s whisker detector, a pair of1N34A germanium diodes are used as rectifiers — one for demodulating the audio signal, and the other to drive a microammeter to indicate signal strength. A cat’s whisker is included for looks, though, mounted to the black acrylic front panel along with nice chunky knobs and homebrew rotary switches for band selection and antenna.

As nice as the details on the electronics are, it’s the case that really sells this build. Using quarter-sawn oak salvaged from old floorboards. The joinery is beautiful and the hardware is period correct; we especially appreciate the work that went into transforming a common flat washer into a nickel-plated escutcheon for the lock — because every radio needs a lock.

Congratulations to [Alvenh] for pulling off such a wonderful build, and really celebrating the craftsmanship of the early days of radio. Need some crystal radio theory before tackling your build? Check out [Greg Charvat]’s crystal radio deep dive.

The Apollo Digital Ranging System: More Than Meets The Eye

April 25, 2022 by 15 Comments

If you haven’t seen [Ken Shirriff]’s teardowns and reverse engineering expeditions, then you’re in for a treat. His explanation and demonstration of the Apollo digital ranging system is a fascinating read, even if vintage computing and engineering aren’t part of your normal fare.

The average Hackaday reader should be familiar with the concept of determining the distance of a faraway object by measuring how long it takes a sound or radio wave to be reflected, such as in sonar and radar. Going another step and measuring Doppler Shift – the difference in the returned signal’s frequency – will tell us the velocity of the object relative to our position. It’s so simple that an Arduino can do it. But in the days of Apollo, there was no Arduino. In fact, there were no Integrated Circuits. And Apollo missions went all the way to the moon- far too distant for relatively simple Radar measurements. Continue reading “The Apollo Digital Ranging System: More Than Meets The Eye” →