Stressless Shortwave Reviewed

March 12, 2024 by Al Williams 17 Comments

[Dan Robinson] picked up a shortwave receiver known as the “stressless” receiver kit. We aren’t sure if the stress is from building a more complicated kit or operating a more complicated receiver. Either way, it is an attractive kit that looks easy to build.

Presumably to reduce stress, the VFO and receiver boards are already built, so assembly is just a few hours connecting large components and boards. As kits go, this is a fairly simple one. We were surprised to read that the supplier says you can’t upgrade the firmware. We, of course, wonder if that’s true.

For technical specs, the receiver is AM only and can operate from 100 kHz to 30 MHz. It uses a double conversion with intermediate frequencies of 21.4 MHz and 455 kHz. There’s a BNC connector on the back, and the radio requires 11 to 15V on the input. Apparently, the frequency generator inside is an SI5351. The sensitivity and selectivity numbers look very good for an AM radio.

We were surprised to see the radio didn’t have provisions for SSB since AM-only makes it not as useful for hams or others interested in non-broadcast transmissions. If we are doing our conversions correctly, the kit is fairly pricey, too, especially considering that it is AM only.

Still, we like that you could easily assemble a nice-looking radio kit. We were interested in hearing it perform, and [Dan’s] video lets us virtually try it out without the effort. We’ve seen the SI5351 on a carrier if you want to roll your own. Come to think of it, we’ve seen several.

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Inside America’s Last Morse Code Station

March 8, 2024 by Al Williams 42 Comments

The Titanic famously (or infamously) used Morse code to call out in distress at the end of its final voyage. Ships at sea and the land-based stations that supported them used Morse code for decades, but with the growing use of satellites, maritime Morse code ended in 1999. With one notable exception. [Saahil Desai] writing in the Atlantic tells the story of America’s last Morse code station, KPH just north of San Francisco.

In fact, KPH did shut down in 1997 as part of the wind down of Morse code in ocean vessels. But some radio enthusiasts, including [Tom Horsfall] and [Richard Dillman], have brought the venerable station back to life. The radio squirrels, as they call themselves, dutifully send news and weather every Saturday to anyone interested in listening. They also exchange radio traffic, primarily with the SS Jeremiah O’Brien, a World War II-era ship parked nearby. N2FQ visited the station and operated the station on video, which you can see below. Or, check out the tour in the second video, below.

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Phenolic board from an RC car - a well-known sight for a hacker

Pairing A New Remote To A Cheap RC Car

March 8, 2024 by Arya Voronova 10 Comments

The cheap little RC cars are abundant anywhere you are, and if you’ve ever disassembled one, you are familiar with how the PCB looks. A single-sided phenolic paper PCB with a mystery chip driving a bunch of through-hole transistors, a sprinkle of through-hole capacitors, and a few supporting components for the wire antenna. It might not feel reusable, but [Chris Jones] begs to differ, with a Twitter thread showing us how he’s paired a scrap board from one RC car with a remote control from another, all to help a little family project.

These mystery ICs turn out to be RC-car-on-a-chip modules, and Chris lucked out in that his IC has a detailed datasheet available, complete with code pulse examples for different commands. The datasheet for the chip in the remote control is nowhere to be found, though, so we have to dig deeper. How about scoping the RF output? Turns out the supported codes between the two ICs are basically identical! The scrap board wouldn’t move any motors though, so it was time to narrow down the issue.

The RC car board has a 128KHz oscillator, and scoping that has shown the issue – it was producing 217KHz for some reason. It turned out that the oscillator’s load resistor was 100 kiloohms instead of recommended 200k, and switching that put it back on course. We would assume that, wherever the original remote control for that car is, it is similarly mis-tuned, or otherwise the RC car could never have worked.

Through sheer luck and tactical application of an oscilloscope, the RC car moves again, paired to a remote it was never meant to be, and the family project moves forward. Got a RC car, but no remote? Perhaps a HackRF can help.

A bias tee module added inside the Starlink terminal, connected to the pads where a GPS antenna used to be wired

GPS Antenna Mods Make Starlink Terminal Immune To Jammers

March 6, 2024 by Arya Voronova 70 Comments

The Starlink receivers need positioning and precise timing information to function, and currently the best way to get that information is to use a global navigation satellite system (GNSS) such as GPS. Unfortunately, the antenna used for this secondary satellite connection leaves something to be desired. Of course, when it comes to solving Starlink problems, there’s no one best than [Oleg Kutkov], whose duty is to fix and improve upon Starlink terminals used in Ukraine — and when the specific problem is GPS bands getting jammed by the invading military, you better believe that a fix is due.

[Oleg] sets the scene, walking us through the evolution of GPS circuitry on the Starlink terminals. Then he shows us the simplest mods you can do, like soldering an improved passive antenna in place of the chip antenna currently being used. Then, he takes it up a notch, and shows us how you could attach an active antenna by using a bias tee module, a mod that would surely work wonders on more than just this device! Then, he brings out the test result tables — and the differences are impressive, in that the Starlink terminals with active antenna mods were able to get GPS signal in areas with active jamming going on, while the unmodified ones could not.

The post is exceptionally accessible, and a must read for anyone wondering about GPS antenna reception problems in customer-accessible devices. This is not the only Starlink hardware mod we’ve seen [Oleg] make, we’ve just covered his Starlink Ethernet port restoration journey that meticulously fixes Ethernet connectivity oversights in the newer models, and the blog also has an article about powering Starlink terminals without the need for PoE, so, do check it out if you’re looking for more!

Making A Crystodyne Radio With Zinc Oxide And Cat’s Whiskers

March 5, 2024 by Maya Posch 19 Comments

Zinc negative resistance oscillator circuit. (Credit: Ashish Derhgawen)

During the first half of the 20th century radio technology was booming, albeit restricted by the vacuum tube technology of the time which made radios cumbersome in size and power needs. The development of a solid state alternative to the vacuum tube was in full swing, but the first version pioneered by [Oleg Losev] in the form of crystal radios failed to compete. Even so these ‘crystal radios’ laid much of the groundwork for subsequent research. The ease of creating this type of radio also makes it a fun physics experiment today, as [Ashish Derhgawen] demonstrates in a blog post.

In the January 1925 issue of Radio News the theory of the circuit is explained by [Oleg Losev] himself (page 1167). At the core is a material capable of negative resistance, as a non-linear (non-Ohmic) material, which means that the current passing through them decreases as voltage increases over part of their I-V curve. This enables it to work as an amplifier or oscillator. After the cessation of research on crystal radio technology by [Losev] and others, the negative resistance diode was rediscovered in 1957 with the tunnel diode.

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Phone connected to the DIY LTE network playing a YouTube video, with antennas in the background

Building Your Own 4G LTE Base Station

March 3, 2024 by Arya Voronova 14 Comments

We’ve seen quite a few DIY 2G networks over the years, but the 4G field has been relatively barren. Turns out, there’s an open source suite called srsRAN that lets you use an SDR for setting up an LTE network, and recently, we’ve found a blog post from [MaFrance351] (Google Translate) that teaches you everything you could need to know if you ever wanted to launch a LTE network for your personal research purposes.

For a start, you want a reasonably powerful computer, a transmit-capable full-duplex software defined radio (SDR), suitable antennas, some programmable SIM cards, and a few other bits and pieces like SIM card programmers and LTE-capable smartphones for testing purposes. Get your hardware ready and strap in, as [MaFrance351] guides you through setting up your own base station, with extreme amounts of detail outlining anything you could get caught up on.

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