Radio Hacks

1338 Articles

CW Not Hard Enough? Try This Tiny Paddle

July 22, 2024 by 7 Comments

For a long time, a Morse code proficiency was required to obtain an amateur radio license in many jurisdictions around the world, which was a much higher bar of entry than most new hams have to pass. Morse, or continuous wave (CW) is a difficult skill to master, and since the requirement has been dropped from most licensing requirements few radio operators pick up this skill anymore. But if you like a challenge, and Morse itself isn’t hard enough for you, you might want to try out this extremely small Morse paddle.

Originally meant for portable operation, where hiking to something like a mountain top with radio gear demands small, lightweight, and low-power options, this paddle is actually not too complex. It attaches to most radios with a 3.5 mm stereo cable and only has two paddles on flexible metal arms which, when pressed against the center of the device, tell the radio to either produce continuous “dits” or “dahs”. For portable use the key sits inside a tiny plastic case and only needs to be pulled out and flipped around to get started. And, while not waterproof, [N6ARA] reports that it’s so small you likely could just shield it from the rain with your other hand if you needed to.

Presumably, this paddle actually wouldn’t be that much different than using any other paddle except for the fact that it’s not heavy enough to resist the force of use, so you’d have to hold it with your other hand anyway. And, while this is a product available for purchase it’s simple enough that, presumably, the design could easily be duplicated with just a few parts. Paddles like this were made as an improvement to older technology like straight keys which require the operator to produce the correct lengths of tones for each character manually. While you can get higher speeds with a paddle, there are still some dedicated CW operators using a straight key.

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Coax Stub Filters Demystified

July 21, 2024 by 9 Comments

Unless you hold a First Degree RF Wizard rating, chances are good that coax stubs seem a bit baffling to you. They look for all the world like short circuits or open circuits, and yet work their magic and act to match feedline impedances or even as bandpass filters. Pretty interesting behavior from a little piece of coaxial cable.

If you’ve ever wondered how stub filters do their thing, [Fesz] has you covered. His latest video concentrates on practical filters made from quarter-wavelength and half-wavelength stubs. Starting with LTspice simulations, he walks through the different behaviors of open-circuit and short-circuit stubs, as well as what happens when multiple stubs are added to the same feedline. He also covers a nifty online calculator that makes it easy to come up with stub lengths based on things like the velocity factor and characteristic impedance of the coax.

It’s never just about simulations with [Fesz], though, so he presents a real-world stub filter for FM broadcast signals on the 2-meter amateur radio band. The final design required multiple stubs to get 30 dB of attenuation from 88 MHz to 108 MHz, and the filter seemed fairly sensitive to the physical position of the stubs relative to each other. Also, the filter needed a little LC matching circuit to move the passband frequency to the center of the 2-meter band. All the details are in the video below.

It’s pretty cool to see what can be accomplished with just a couple of offcuts of coax. Plus, getting some of the theory behind those funny little features on PCBs that handle microwave frequencies is a nice bonus. This microwave frequency doubler is a nice example of what stubs can do.

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A Nostalgic Look At A Kid’s Shortwave Receiver

July 18, 2024 by 10 Comments

[Mikrowave1] had a Unelco shortwave receiver as a kid. This was a typical simple radio for the 1960s using germanium and silicon transistors. It also had plug-in coils you had to insert into sockets depending on the frequency band you wanted to receive.

While simple AM radios were all the rage, they didn’t have to operate at higher frequencies. [Mikrowave1] shows some of the design tricks used to allow the radio to operate in the upper part of the spectrum. Otherwise, the radio is the usual superhet design using lower frequency germanium PNP transistors in the IF stage. You get a look inside the radio and a peek at a similar schematic along with notes on where the radio is different.

But how does it work? For an old single-conversion receiver, it works well enough. Of course, when the radio was new, there were many more interesting stations on shortwave. Today, he had to settle for some ham radio stations and CHU, the Canadian time and frequency station.

There were six pairs of coils built on top of tube sockets. The coil was actually more than a coil. There were other components in the case that adjusted other radio parameters based on the frequency.

[Mikrowave1] has been on a toy kick lately, and we’ve enjoyed it. This radio looks simple compared to the Radio Shack one that every kid wanted in the 1970s. Well. Every hacker kid, at least.

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Are Hackers The Future Of Amateur Radio?

July 18, 2024 by 120 Comments

If amateur radio has a problem, it’s that shaking off an image of being the exclusive preserve of old men with shiny radios talking about old times remains a challenge. Especially, considering that so many amateurs are old men who like to talk a lot about old times. It’s difficult to attract new radio amateurs in the age of the Internet, so some in the hobby are trying new avenues. [Dan, KB6NU] went to the recent HOPE conference to evangelise amateur radio, and came away having had some success. We agree with him, hackers can be the future of amateur radio.

He’s put up the slides from his talk, and in them he goes through all the crossovers between the two communities from Arduinos to GNU Radio. We don’t need persuading, in fact we’d have added UHF and microwave RF circuitry and pushing the limits of the atmosphere with digital modes such as WSPR to the list as our personal favourites. It seems he found willing converts, and it’s certainly a theme we’ve featured before here at Hackaday. After all, unless it retains its interest, amateur radio could just die away.

DME With A Twist Of LimeSDR

July 16, 2024 by No comments

Navigating aircraft today isn’t like the old days. No more arrows painted on a barn roof or rotating airway beacons. Now, there are a host of radio navigation aids. GPS, of course, is available. But planes often use VOR to determine a bearing to a known point and DME — distance measuring equipment — to measure the distance to that point. DME operates around 1000 MHz and is little more than a repeater. An airplane sends a pair of pulses, and times how long it takes for the DME to repeat them. [Daniel Estévez] has been monitoring these transmissions with a LimeSDR.

Like most repeaters, the DME transponders listen on one frequency and transmit on another. Those frequencies are 63 MHz apart. This poses a challenge for some types of SDRs which have limits on bandwidth.

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Tiny Transceiver Gets It Done With One Transistor

July 12, 2024 by 23 Comments

When we first spotted the article about a one-transistor amateur radio transceiver, we were sure it was a misprint. We’ve seen a lot of simple low-power receivers using a single transistor, and a fair number of one-transistor transmitters. But both in one package with only a single active component? Curiosity piqued.

It turns out that [Ciprian Popica (YO6DXE)]’s design is exactly what it says on the label, and it’s pretty cool to boot. The design is an improvement on a one-transistor transceiver called “El Pititico” and is very petite indeed. The BOM has only about fifteen parts including a 2N2222 used as a crystal-controlled oscillator for both the transmitter and the direct-conversion receiver, along with a handful of passives and a coupe of hand-wound toroidal inductors. There’s no on-board audio section, so you’ll have to provide an external amplifier to hear the signals; some might say this is cheating a bit from the “one transistor” thing, but we’ll allow it. Oh, and there’s a catch — you have to learn Morse code, since this is a CW-only transmitter.

As for construction, [Ciprian] provides a nice PCB  layout, but the video below seems to show a more traditional “ugly style” build, which we always appreciate. The board lives in a wooden box small enough to get lost in a pocket. The transceiver draws about 1.5 mA while receiving and puts out a fairly powerful 500 mW signal, which is fairly high in the QRP world. [Ciprian] reports having milked a full watt out of it with some modifications, but that kind of pushes the transistor into Magic Smoke territory. The signal is a bit chirpy, too, but not too bad.

We love minimalist builds like these; they always have us sizing up our junk bin and wishing we were better stocked on crystals and toroids. It might be good to actually buckle down and learn Morse too.

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Hackable Ham Radio Gives Up Its Mechanical Secrets

July 9, 2024 by 4 Comments

Reverse-engineered schematics are de rigeur around these parts, largely because they’re often the key to very cool hardware hacks. We don’t get to see many mechanical reverse-engineering efforts, though, which is a pity because electronic hacks often literally don’t stand on their own. That’s why these reverse-engineered mechanical diagrams of the Quansheng UV-K5 portable amateur radio transceiver really caught our eye.

Part of the reason for the dearth of mechanical diagrams for devices, even one as electrically and computationally hackable as the UV-K5, is that mechanical diagrams are a lot less abstract than a schematic or even firmware. Luckily, this fact didn’t daunt [mdlougheed] from putting a stripped-down UV-K5 under a camera for a series of images to gather the raw data needed by photogrammetry package RealityCapture. The point cloud was thoughtfully scaled to match the dimensions of the radio’s reverse-engineered PC board, so the two models can work together.

The results are pretty impressive, especially for a first effort, and should make electromechanical modifications to the radio all the easier to accomplish. Hats off to [mdlougheed] for the good work, and let the mechanical hacks begin.