Radio Hacks

1317 Articles

Two-Tube Spy Transmitter Fits In The Palm Of Your Hand

March 29, 2023 by 13 Comments

It’s been a long time since vacuum tubes were cutting-edge technology, but that doesn’t mean they don’t show up around here once in a while. And when they do, we like to feature them, because there’s still something charming, nay, romantic about a circuit built around hot glass and metal. To wit, we present this compact two-tube “spy radio” transmitter.

From the look around his shack — which we love, by the way — [Helge Fykse (LA6NCA)] really has a thing for old technology. The typewriter, the rotary phones, the boat-anchor receiver — they all contribute to the retro feel of the space, as well as the circuit he’s working on. The transmitter’s design is about as simple as can be: one tube serves as a crystal-controlled oscillator, while the other tube acts as a power amplifier to boost the output. The tiny transmitter is built into a small metal box, which is stuffed with the resistors, capacitors, and homebrew inductors needed to complete the circuit. Almost every component used has a vintage look; we especially love those color-coded mica caps. Aside from PCB backplane, the only real nod to modernity in the build is the use of 3D printed forms for the coils.

But does it work? Of course it does! The video below shows [Helge] making a contact on the 80-meter band over a distance of 200 or so kilometers with just over a watt of power. The whole project is an excellent demonstration of just how simple radio communications can be, as well as how continuous wave (CW) modulation really optimizes QRP setups like this.

Continue reading “Two-Tube Spy Transmitter Fits In The Palm Of Your Hand” →

Hams Watch For Meteors

March 28, 2023 by 13 Comments

After passing an exam and obtaining a license, an amateur radio operator will typically pick up a VHF ratio and start talking to other hams in their local community. From there a whole array of paths open up, and some will focus on interesting ways of bouncing signals around the atmosphere. There are all kinds of ways of propagating radio waves and bouncing them off of various reflective objects, such as the Moon, various layers of the ionosphere, or even the auroras, but none are quite as fleeting as bouncing a signal off of a meteor that’s just burned up in the atmosphere.

While they aren’t specifically focused on communicating via meteor bounce, The UK Meteor Beacon Project hopes to leverage amateur radio operators and amateur radio astronomers to research more about meteors as they interact with the atmosphere. A large radio beacon, which has already been placed into service, broadcasts a circularly-polarized signal in the six-meter band which is easily reflected back to Earth off of meteors. Specialized receivers can pick up these signals, and are coordinated among a network of other receivers which stream the data they recover over the internet back to a central server.

With this information, the project can determine where the meteor came from, some of the properties of the meteors, and compute their trajectories by listening for the radio echoes the meteors produce. While this is still in the beginning phases and information is relatively scarce, the receivers seem to be able to be built around RTL-SDR modules that we have seen be useful across a wide variety of radio projects for an absolute minimum of cost.

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Long-Distance Gaming Over Packet Radio

March 27, 2023 by 25 Comments

The amateur radio community often gets stereotyped as a hobby with a minimum age requirement around 70, gatekeeping airwaves from those with less experience or simply ignoring unfamiliar beginners. While there is a small amount of truth to this on some local repeaters or specific frequencies, the spectrum is big enough to easily ignore those types and explore the hobby without worry (provided you are properly licensed). One of the best examples of this we’ve seen recently of esoteric radio use is this method of using packet radio to play a game of Colossal Cave Adventure.

Packet radio is a method by which digital information can be sent out over the air to nodes, which are programmed to receive these transmissions and act on them. Typically this involves something like email or SMS messaging, so playing a text-based game over the air is not too much different than its intended use. For this build, [GlassTTY] aka [G6AML] is using a Kenwood TH-D72 which receives the packets from a Mac computer. It broadcasts these packets to his node, which receives these packets and sends them to a PDP-11 running the game. Information is then sent back to the Kenwood and attached Mac in much the same way as a standard Internet connection.

The unique features of packet radio make it both an interesting and useful niche within the ham radio community, allowing for all kinds of uses where data transmission might otherwise be infeasible or impossible. A common use case is APRS, which is often used on VHF bands to send weather and position information out, but there are plenty of other uses for it as well.

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Recreating One Of History’s Best Known Spy Gadgets

March 25, 2023 by 22 Comments

[Machining and Microwaves] got an interesting request. The BBC asked him to duplicate the Great Seal Bug — the device the Russians used to listen covertly to the US ambassador for seven years in 1945. Turns out they’re filming a documentary on the legendary surveillance device and wanted to demonstrate how it worked.

The strange thing about the bug is that it wasn’t directly powered. It was actually a resonant cavity that only worked when it was irradiated with an external RF energy. Most of the video is background about the bug, with quite a few details revealed. We particularly liked the story of using a software defined radio (SDR) to actually make the bug work.

As you might expect, things didn’t go smoothly. Did they ever get results on camera? Watch the video, and you can find out. This is just the first of six videos he plans to make on the topic, and we can’t wait for future videos that cover the machining and more technical details.

We’ve examined the Theremin bug before. There’s a definite cat-and-mouse dynamic between creating bugging devices and detecting them.

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Enormous Metal Sculpture Becomes An Antenna

March 23, 2023 by 16 Comments

Those who have worked with high voltage know well enough that anything can be a conductor at high enough voltages. Similarly, amateur radio operators will jump at any chance to turn a random object into an antenna. Flag poles, gutters, and even streams of water can be turned into radiating elements for a transmitter, but the members of this amateur radio club were thinking a little bit bigger when they hooked up their transmitter to this giant sculpture.

For those who haven’t been to the Rochester Institute of Technology (RIT) in upstate New York, the enormous metal behemoth is not a subtle piece of artwork and sits right at the entrance to the university. It’s over 70 feet tall and made out of bronze and steel, a dream for any amateur radio operator. With the university’s permission and some help to ensure everyone’s safety during the operation, the group attached a feedline to the sculpture with a magnet, while the shield wire was attached to a ground rod nearby. A Yaesu FT-991 running on only 5 watts and transmitting in the 20-meter band was able to make contacts throughout much of the eastern United States with this setup.

This project actually started as an in-joke within the radio club, as reported by Reddit user [bbbbbthatsfivebees] who is a member. Eventually the joke became reality, as the sculpture is almost a perfect antenna for certain ham bands. Others in the comments noted that they might have better luck with lower frequency bands such as the 40-meter band or possibly the 60-meter band, due to the height of the structure. And, for those who are still wondering if you really can use a stream of water to transmit radio waves, it is indeed possible.

Info Sought On A Forgotten Cuban Radio

March 21, 2023 by 11 Comments

Some of the daily normalities of life in the Cold War seem a little surreal from our perspective in 2023, when nuclear bombers no longer come in to land just down the road and you can head off to Poland or Czechia on a whim. Radio amateurs were one of the few groups of civilians whose activities crossed the geopolitical divide, and even though an operator on the other side from ours couldn’t buy a shiny Japanese radio, their homebrew skills matched anything we could do with our Western soldering irons.

[Bill Meara N2CQR] is particularly interested in one line of Cold War-era Communist homebrew radios, the tube-based Cuban “Islander” and its solid-state “Jaguey” sibling. It’s a homebrew double-sideband transceiver design built using readily-available Soviet TV parts, and though he’s published what he can find, he’s on the lookout for more info about these interesting rigs.

The mechanics of a DSB transceiver are simple enough, in that an oscillator and balanced mixer can serve as both modulator and as direct conversion receiver. The fuzzy black and white photographs give frustratingly little detail, but we’re impressed by the quality of what we can see. We have readers all over the world (including we hope, some in Cuba), so perhaps if you know something about these radios you can give Joe a hand. It’s a design that deserves to be appreciated.

For more epic Cold War hackery on the Communist side, read our colleague [Voja Antonic]’s story of his personal computer odyssey.

Cold War Listening Post Antennas

March 20, 2023 by 32 Comments

With a UHF antenna, it is easy to rotate a directional antenna to find the bearing to a transmitter. But at HF, it is more common to use an array of antennas that you can electrically switch as well as analyze the phase information between the elements. [Ringway Manchester] has a look at the “elephant cage” antenna used by the US Iron Horse listening network from the 1950s. You can see a video about the giant antenna system, the AN/FLR-9.

Technically, the ring of concentric antenna elements forms a Wullenweber antenna. The whole thing consists of three rings built on a ground screen nearly 1,500 feet across. The outer ring covers from 1.5 to 6 MHz or band A. The band B ring in the center covers 6 to 18 MHz. The inner ring covers band C which was from 18 to 30 MHz.  Band A was made up of 48 monopoles while band B used 96 elements. The much smaller band C elements were 48 pairs of horizontally polarized dipoles. Continue reading “Cold War Listening Post Antennas” →