Cheap DIY High Impedance Earphones

December 3, 2020 by Lewin Day 18 Comments

Crystal radios can feel magical, given their ability to tune in audio from distant stations with nothing but the energy from the radio signal itself. However, to achieve this feat, they typically rely on a high-impedance earphone to produce an audible sound with very little current. These earphones are hard to find, and thus can be expensive. However, [Billy] figured out a way to build them on the cheap.

The build starts with a common piezoelectric buzzer. It’s torn down and the extraneous circuitry inside is removed. The piezo element itself is then directly hooked up to a mono audio jack for use with one of [Billy’s] crystal radios. To make it into a usable earpiece, the tip of a pen is cut off and glued to the buzzer’s plastic housing. Then, a rubber in-ear cup from regular modern earbuds is used to ensure a tight, comfortable fit in the ear.

It’s a great way to build something that’s now hard to source, and we bet that [Billy’s] design is more comfortable than the hard plastic models that shipped in Radio Shack kits in the 90s. Of course, there’s other ways to build high-impedance drivers, as we’ve featured before. And, if you’re looking to build a crystal radio, it’s hard to go past [Billy’s] credit card chip build. Video after the break.

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Gathering Eclipse Data Via Ham Radio

November 30, 2020 by Bryan Cockfield 12 Comments

A solar eclipse is coming up in just a few weeks, and although with its path of totality near the southern tip of South America means that not many people will be able to see it first-hand, there is an opportunity to get involved with it even at an extreme distance. PhD candidate [Kristina] and the organization HamSCI are trying to learn a little bit more about the effects of an eclipse on radio communications, and all that is required to help is a receiver capable of listening in the 10 MHz range during the time of the eclipse.

It’s well-known that certain radio waves can propagate further depending on the time of day due to changes in many factors such as the state of the ionosphere and the amount of solar activity. What is not known is specifically how the paths can vary over the course of the day. During the eclipse the sun’s interference is minimized, and its impact can be more directly measured in a more controlled experiment. By tuning into particular time stations and recording data during the eclipse, it’s possible to see how exactly the eclipse impacts propagation of these signals. [Kristina] hopes to take all of the data gathered during the event to observe the doppler effect that is expected to occur.

The project requires a large amount of volunteers to listen in to the time stations during the eclipse (even if it is not visible to them) and there are only a few more days before this eclipse happens. If you have the required hardware, which is essentially just a receiver capable of receiving upper-sideband signals in 10 MHz range, it may be worthwhile to give this a shot. If not, there may be some time to cobble together an SDR that can listen in (even an RTL-SDR set up for 10 MHz will work) provided you can use it to record the required samples. It’s definitely a time that ham radio could embrace the hacker community.

Ham Radio Needs To Embrace The Hacker Community Now More Than Ever

November 28, 2020 by Jenny List 236 Comments

As many a radio amateur will tell you, ham radio is a hobby with as many facets as there are radio amateurs. It should be an exciting and dynamic place to be, but as those who venture forth into it sometimes sadly find out, it can be anything but. Tightly-knit communities whose interests lie in using $1,000 stations to chase DX (long-distance contacts), an advancing age profile, and a curious fascination of many amateurs with disaster communications. It’s something [Robert V. Bolton, KJ7NZL] has sounded off about in an open letter to the amateur radio community entitled “Ham Radio Needs To Embrace The Hacker Community Now More Than Ever“.

In it he laments that the influx in particular of those for whom disaster preparedness is the reason for getting a licence is to blame for amateur radio losing its spark, and he proposes that the hobby should respond by broadening its appeal in the direction of the hacker community. The emphasis should move from emergency communications, he says, and instead topics such as software defined radio and digital modes should be brought to the fore. Finally he talks about setting up hacker specific amateur radio discussion channels, to provide a space in which the talk is tailored to our community.

Given our experience of the amateur radio community we’d be bound to agree with him. The hobby offers unrivalled opportunity for analogue, mixed-signal, digital, and software tinkering in the finest tradition of the path set by the early radio amateurs around a hundred years ago, yet it sometimes seems to have lost its way for people like us. It’s something put into words a few years ago by our colleague Dan Maloney, and if you’re following [KJ7NZL]’s path you could do worse than read Dan’s long-running $50 ham series from the start.

Via Hacker News.

Header image: Unknown author, Public domain.

HackRF PortaPack Firmware Spoofs All The Things

November 28, 2020 by Tom Nardi 45 Comments

The HackRF is an exceptionally capable software defined radio (SDR) transceiver, but naturally you need to connect it to a computer to actually do anything with it. So the PortaPack was developed to turn it into a stand-alone device with the addition of a touchscreen LCD, a few buttons, and a headphone jack. With all the hardware in place, it’s just a matter of installing a firmware capable enough to do some proper RF hacking on the go.

Enter MAYHEM, an evolved fork of the original PortaPack firmware that the developers claim is the most up-to-date and feature packed version available. Without ever plugging into a computer, this firmware allows you to receive, decode, and re-transmit a dizzying number of wireless protocols. From firing off the seating pagers at a local restaurant to creating a fleet of phantom aircraft with spoofed ADS-B transponders, MAYHEM certainly seems like it lives up to the name.

[A. Petazzoni] recently put together a detailed blog post about installing and using MAYHEM on the HackRF/PortaPack, complete with a number of real-world examples that show off just a handful of possible applications for the project. Jamming cell phones, sending fake pager messages, and cloning RF remotes is just scratching the surface of what’s possible.

It’s not hard to see why some have already expressed concern about the project, but in reality, none of these capabilities are actually new. This firmware simply brings them all together in one easy-to-use package, and while there might be an argument to be made about proliferation, we all know that the responsibility to behave ethically rests on the user and not the tools.

Real Spectrum Analysis Goes Virtual

November 24, 2020 by Al Williams 4 Comments

One of the hard things about electronics is that you can’t really see the working parts without some sort of tool. If you work on car engines, fashion swords, or sculpt clay, you can see with your unaided eye what’s going on. Electronic components are just abstract pieces and the real action requires a meter or oscilloscope to understand. Maybe that’s what [José] was thinking of when he built a-radio. This “humble experiment” pipes a scan from a software-defined radio into VR goggles, which can be as simple as a smartphone and some cardboard glasses.

The resulting image shows you what the radio spectrum looks like. Granted, so will a spectrum analyzer, but perhaps the immersion will provide a different kind of insight into radio frequency analysis.

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Coaxial Connectors, Starting With The PL259

November 23, 2020 by Jenny List 30 Comments

For the casual breadboard experimenter with a microcontroller and a few peripherals, there’s little concern over interconnects as a set of jumper wires will suffice. But as any radio amateur will tell you though, at higher frequencies it’s a very different affair. [Ria Jairam N2RJ] has embarked upon a series of videos exploring co-axial cable and its various connectors, and her first offering features the humble UHF connector, sometimes known as the PL259. Though it’s one of the older choices and its design flaws mean that “UHF” is more of an aspiration for it than a reality, it remains a common connector at the lower end of the amateur radio frequency range.

She starts with a brief history of co-axial cable, before introducing the UHF connector. We’re the introduced to its major flaw, in that it doesn’t present a constant impedance. The resulting mismatch presents a significant problem to a transmitter, especially at higher frequencies. We’re then taken through the various different models of UHF connector, including those with honeycomb dielectric to minimize the mismatch, and the fancy expensive plugs with strain relief. Finally she takes us through the proper fitting of a PL259 plug, something that there’s a bit more to than most of us might think. Altogether it’s an interesting and informative watch from an engaging and knowledgeable host, and we look forward to more.

Meanwhile, the field of RF connectors is something we’ve dipped a to into from time to time ourselves.

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Portable Ham Antenna Uses SMD Capacitors

November 17, 2020 by Al Williams 13 Comments

[K6ARK] likes to operate portable, so he puts together very lightweight antennas. One of his latest uses tiny toroids and SMD capacitors to form trap elements. You can see the construction of it in the video below.

You usually think of toroid winding as something you do when building transmitters or receivers, especially small ones like these. We presume the antenna is best for QRP (low power) operation since the tiny core would saturate pretty quickly at higher power. Exactly how much power you should pass through an FT50-43 core depends on the exact application, but we’ve seen numbers around 5 watts.

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