radio

545 Articles

Writing A GPS Receiver From Scratch

March 18, 2025 by 22 Comments

GPS is an incredible piece of modern technology. Not only does it allow for locating objects precisely anywhere on the planet, but it also enables the turn-by-turn directions we take for granted these days — all without needing anything more than a radio receiver and some software to decode the signals constantly being sent down from space. [Chris] took that last bit bit as somewhat of a challenge and set off to write a software-defined GPS receiver from the ground up.

As GPS started as a military technology, the level of precision needed for things like turn-by-turn navigation wasn’t always available to civilians. The “coarse” positioning is only capable of accuracy within a few hundred meters so this legacy capability is the first thing that [Chris] tackles here. It is pretty fast, though, with the system able to resolve a location in 24 seconds from cold start and then displaying its information in a browser window. Everything in this build is done in Python as well, meaning that it’s a great starting point for investigating how GPS works and for building other projects from there.

The other thing that makes this project accessible is that the only other hardware needed besides a computer that runs Python is an RTL-SDR dongle. These inexpensive TV dongles ushered in a software-defined radio revolution about a decade ago when it was found that they could receive a wide array of radio signals beyond just TV.

Red and gold bakelite Philco farm radio on a workbench

Hacking A Heavyweight Philco Radio

March 10, 2025 by 6 Comments

There’s something magical about the clunk of a heavy 1950s portable radio – the solid thunk of Bakelite, the warm hum of tubes glowing to life. This is exactly why [Ken’s Lab] took on the restoration of a Philco 52-664, a portable AC/DC radio originally sold for $45 in 1953 (a small fortune back then!). Despite its beat-up exterior and faulty guts, [Ken] methodically restored it to working condition. His video details every crackling capacitor and crusty resistor he replaced, and it’s pure catnip for any hacker with a soft spot for analog tech. Does the name Philco ring a bell? Lately, we did cover the restoration of a 1958 Philco Predicta television.

What sets this radio hack apart? To begin with, [Ken] kept the restoration authentic, repurposing original capacitor cans and using era-appropriate materials – right down to boiling out old electrolytics in his wife’s discarded cooking pot. But, he went further. Lacking the space for modern components, [Ken] fabbed up a custom mounting solution from stiff styrofoam, fibreboard, and all-purpose glue. He even re-routed the B-wiring with creative terminal hacks. It’s a masterclass in patience, precision, and resourcefulness.

If this tickles your inner tinkerer, don’t miss out on the full video. It’s like stepping into a time machine.

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Dismanteled Hallicrafters radio on workbench

Shortwave Resurrection: A Sticky Switch Fix On A Hallicrafters

March 4, 2025 by 10 Comments

Shortwave radio has a charm all its own: part history, part mystery, and a whole lot of tech nostalgia. The Hallicrafters S-53A is a prime example of mid-century engineering, but when you get your hands on one, chances are it won’t be in mint condition. Which was exactly the case for this restoration project by [Ken’s Lab], where the biggest challenge wasn’t fried capacitors or burned-out tubes, but a stubborn band selector switch that refused to budge.

What made it come to this point? The answer is: time, oxidation, and old-school metal tolerances. Instead of forcing it (and risking a very bad day), [Ken]’s repair involved careful disassembly, a strategic application of lubricant, and a bit of patience. As the switch started to free up, another pleasant surprise emerged: all the tubes were original Hallicrafters stock. A rare find, and a solid reason to get this radio working without unnecessary modifications. Because some day, owning a shortwave radio could be a good decision.

Once powered up, the receiver sprang to life, picking up shortwave stations loud and clear. Hallicrafters’ legendary durability proved itself once before, in this fix that we covered last year. It’s a reminder that sometimes, the best repairs aren’t about drastic changes, but small, well-placed fixes.

What golden oldie did you manage to fix up?

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Communicating With Satellites Like It’s 1957

February 3, 2025 by 14 Comments

When the first artificial satellite, Sputnik, was put into orbit around Earth, anyone in the path of the satellite could receive the beeps transmitted by the satellite provided they had some simple radio equipment. Of course, there was no two-way communication with this satellite, and it only lasted a few weeks before its batteries died. Here in the future, though, there are many more satellites in orbit and a few are specifically meant for ham radio operators. And, like the ’50s, it doesn’t take too much specialized equipment to communicate with them, although now that communication can be two-way.

The first step in this guide by [W2PAK] is to know where these satellites are in the sky. The simplest way to do that is to use a smartphone app called GoSatWatch and, when configured for a specific location, shows the satellites currently overhead. After that it’s time to break out the radio gear, which can be surprisingly inexpensive. A dual-band handheld is required since satellite uplink and downlink can be on different bands, and the antenna can be made from simple parts as well as [W2PAK] demonstrates in a separate video. Combined, this can easily be done for less than $100. [W2PAK] also goes over the proper format and etiquette for a satellite contact as well, so a new operator can pick it up quickly.

Using satellites as repeaters opens up a lot of capabilities when compared to terrestrial communications. Especially for operators with entry-level licenses who are restricted to mostly VHF and UHF, it adds a challenge as well as significantly increased range compared to ground-based repeaters and line-of-sight communications. There are plenty of activities around satellites that don’t require a license at all, too, like this project which downloads weather imagery from weather satellites.

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Bouncing Signals Off Of Satellites Other Than The Moon

January 24, 2025 by 8 Comments

The moon is a popular target for ham radio operators to bounce signals since it’s fairly large and follows a predictable path. There are some downsides, though; it’s not always visible from the same point on Earth and is a relatively long way away. Thinking they could trade some distance for size, an amateur radio group from the Netherlands was recently able to use a radio telescope pointed at a geostationary satellite to reflect a signal back down to Earth, using this man-made satellite to complete the path instead of the more common natural one.

While there are plenty of satellites in orbit meant for amateur radio communication (including the International Space Station, although it occasionally does other things too), these all have built-in radio transmitters or repeaters specifically meant for re-transmitting received signals. They’re also generally not in geostationary orbit. So, with a retired radio telescope with a 20-meter dish aimed directly at one of the ones already there, they sent out a signal which bounced off of the physical body of the satellite and then back down where it was received by a station in Switzerland. Of course, the path loss here is fairly extreme as well since the satellite is small compared to the moon and geostationary orbit is a significant distance away, so they used the Q65 mode in WSJT-X which is specifically designed for recovering weak signals.

Don’t break out the tape measure Yagi antenna to try this yourself just yet, though. This path is not quite as reliable as Earth-Moon-Earth for a few reasons the group is not quite sure about yet. Not every satellite they aimed their dish at worked, although they theorize that this might be because of different shapes and sizes of the satellites or that the solar panels were not pointing the correct direction. But they were able to make a few contacts using this method nonetheless, a remarkable achievement they can add to their list which includes receiving a signal from one of the Voyager spacecraft.

Android Head Unit Gets Volume Knob Upgrade

January 17, 2025 by 22 Comments

Touch screen head units are pretty much the norm these days. Many compromise with annoying on-screen volume controls or tiny buttons. If you find yourself with such a unit, you  might like to hack in a real volume knob. [Daniel Ross] shows us how to do just that.

The build uses an ATMega328 as the heart of the operation, though [Daniel] notes an Arduino Uno or Mini would have done just fine. It’s set up with a 74HC14 hex Schmitt trigger, and a CD4066 quad bilateral switch on a custom PCB. As for the volume knob itself, it’s not a real analog pot, instead it’s using a rotary encoder with a center push button. The way it works is that the Arduino reads the encoder, and figures out whether you’re trying to turn the volume up or down based on the direction you’re turning it. It then sends commands to the CD4066 to switch resistors in and out of circuit with lines going to the stereo to emulate the action of volume buttons on the steering wheel.

[Daniel’s] guide explains how everything works in greater detail, and how you can calibrate your head unit to accept these signals while preserving the function of your actual steering wheel volume buttons. Then you just have to find a neat way to integrate the knob into your existing dashboard.

We don’t see as many car stereo hacks in this era when infotainment systems rule all, but we’ve seen some great stuff from older vehicles over the years. Video after the break.

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All-Band Receiver Lets You Listen To All The Radio At Once

January 9, 2025 by 52 Comments

There are many ways to build a radio receiver, but most have a few things in common, such as oscillators, tuned circuits, detectors, mixers, and amplifiers. Put those together in the right order and you’ve got a receiver ready to tune in whatever you want to listen to. But if you don’t really care about tuning and want to hear everything all at once, that greatly simplifies the job and leaves you with something like this homebrew all-band receiver.

Granted, dispensing with everything but a detector and an audio amplifier will seriously limit any receiver’s capabilities. But that wasn’t really a design concern for [Ido Roseman], who was in search of a simple and unobtrusive way to monitor air traffic control conversations while flying. True, there are commercially available radios that tune the aviation bands, and there are plenty of software-defined radio (SDR) options, but air travel authorities and fellow travelers alike may take a dim view of an antenna sticking out of a pocket.

So [Ido] did a little digging and found a dead-simple circuit that can receive signals from the medium-wave bands up into the VHF range without regard for modulation. The basic circuit is a Schottky diode detector between an antenna and a high-gain audio amplifier driving high-impedance headphones; [Ido] built a variation that also has an LM386 amplifier stage to allow the use of regular earbuds, which along with a simple 3D-printed case aids in the receiver’s stealth.

With only a short piece of wire as an antenna, reception is limited to nearby powerful transmitters, but that makes it suitable for getting at least the pilot side of ATC conversations. It works surprisingly well — [Ido] included a few clips that are perfectly understandable, even if the receiver also captured things like cell phones chirping and what sounds like random sferics. It seems like a fun circuit to play with, although with our luck we’d probably not try to take it on a plane.