Radio Hacks

1329 Articles

This Standalone Camera Gets The Picture Through With SSTV

November 20, 2022 by 12 Comments

These days, sending a picture to someone else is as simple as pulling out your smartphone and sending it by email or text message. It’s so simple a child can do it, but that simple user experience masks a huge amount of complexity, from the compression algorithms in the phones to the huge amount of distributed infrastructure needed to connect them together. As wonderful and enabling as all that infrastructure can be, sometimes it’s just too much for the job.

That seems to have been the case for [Dzl TheEvilGenius], who just wanted to send a low-resolution image from a remote location. It turns out that hams solved that problem about 70 years ago with slow-scan television, or SSTV. While most of the world was settling down in front of “I Love Lucy” on the regular tube, amateur radio operators were figuring out how to use their equipment to send pictures around the world. But where hams of yore had to throw a considerable amount of gear at the problem, [Dzl] just used an ESP-32 with a camera and some custom code to process the image. The output from one of the MCU’s GPIO pins is a PWM audio signal which can be fed directly into the microphone input of a cheap portable transceiver.

To decode the signal, [Dzl] used one of the many SSTV programs available. There’s no mention of the receiver, although it could be pretty much anything from another Baofeng to an SDR dongle. The code is available in the article, as is an audio file of an encoded image, if you just want to play around with the receiving and decoding side of the equation.

We could see something like this working for a remote security camera, or even for scouting hunting spots. If you want to replicate this, remember that you’ll need a license if you want to transmit on the ham bands — relax, it’s easy.

The KrakenSDR in its metal case, with five small antennas connected to it

Open-Source Passive Radar Taken Down For Regulatory Reasons

November 19, 2022 by 92 Comments

Open-source technology brings a world that laws and regulations are not quite prepared for. As a result, every now and then, open projects need to work around governmental regulations. In today’s news, KrakenRF team has stumbled into an arms-trafficing legal roadblock for their KrakenSDR-based passive radar code, and is currently figuring it out. There’s no indication that there’s been any legal action from the USA government – the team’s being proactive, as fas as we’re told.

KrakenSDR hardware, to simplify it a lot, is five RTL-SDRs on one PCB – with plenty of work put in to do it the right way. It gets you much further than a few dongles – there’s shielded case, suitable connectors, reliable power distribution, a proper USB hub, and importantly, receiver synchronization hardware. Naturally, there’s nice things you can build with such a hefty package – one of them is passive radar, which was a prominent selling point on both KrakenSDR’s pre-launch page back in 2021, and on their crowdfunding page just a week ago. How does that work?

There’s RF emissions floating around you in the air, unless you’re at sea or in the desert. Whether it’s airplane transponders, cell towers, or a crappy switch-mode PSU, the radiowaves emitted interact with objects all around you. If you have multiple receivers with directional antennas, you can catch waves being reflected from some object, compare the wave reflected wave to the wave received from the initial source, and determine the object’s properties like location and speed. If you’d like to know more, IEEE Spectrum has covered this topic just a week ago, and the previously-deleted KrakenSDR wiki page has more details for you to learn from.

Through exposure in IEEE Spectrum, the KrakenSDR work has received plenty of attention and comments. And this is where the International Traffic in Arms Regulations (ITAR) laws come in. We’re not lawyers, but it does look like passive radar is on the list. Today, the code repository and the documentation pages are scrubbed clean while the team is talking to legal experts.

Dealing with this is intimidating, and we wish them luck in clearing this with legal. In the bad old days, certain encryption algorithms were famously in scope, which appeared absolutely ridiculous to us at the time. The laws did eventually change to better reflect reality, but the wheels of justice turn slowly.

Word Tour Map of High Altitude Balloon Launched at Hackaday Supercon.

Supercon Balloon W6MRR-26 Continues Its World Tour

November 18, 2022 by 16 Comments

[Martin Rothfield] and other amateur radio operators from San Francisco High Altitude Ballooning (SF-HAB) treated conference attendees to the 2022 Hackaday Supercon to the launch of two High Altitude Balloons (HABs). On the morning of November 6th, the two balloons were launched from a park across the street from Supplyframe DesignLab in Pasadena, California.

Seven days after its launch from Southern California, one of the balloons was over Tajikistan cruising eastward at an altitude of 42,000 feet (12,800 meters). Balloon W6MRR-26 was already approaching China where it will continue its wonderful world tour to parts unknown. The second balloon (call sign W3HAC-11) landed in northern Arizona where it has continued transmitting whenever it receives power from the sun.

Each balloon carries a tiny payload — a printed circuit board powered only by small photovoltaic cells. The board includes a microcontroller, a GPS module, and a Weak Signal Propagation Reporter (WSPR) radio transmitter.  The transmitted operates on the 20 meter amateur radio band at around 14 MHz.

WSPR beacons can provide time, altitude, and location information.  The WSPR telemetry is then relayed via WSPRgates using Automatic Packet Reporting System (APRS) onto the Internet. The collected information can be viewed and mapped on websites such as aprs.fi.

Continue reading “Supercon Balloon W6MRR-26 Continues Its World Tour” →

Number Stations Gone Wild

November 17, 2022 by 18 Comments

[Ringway Manchester] has an interest in numbers stations. These mysterious stations send presumably coded numbers or other coded information. However, it is rare that anyone claims credit for these stations. Normally they operate with military-like precision, adhering to strict operating schedules and sending out their messages error-free. [Ringway] looks at five times when things didn’t go as planned for these spy stations.

Perhaps it isn’t surprising, however, as machines have likely replaced human operators. That makes them prone to errors when the computers go awry. Many of the errors are ones of frequency, where two number stations wind up transmitting at once. We suppose spies all use the same few frequencies. Some, however, also had computers go haywire and start going through the alphabet which, of course, could have been part of some secret message protocol, but appeared more likely to be a simple mistake.

We were amused, though, to hear the story of a Czech spy station that not only had a licensed call sign but would send QSL cards to people who reported reception. Perhaps they didn’t get the memo about secrecy!

We’ve listened to a few number stations in our time. If you don’t have a suitable antenna, you can always try hunting them online. But don’t expect to catch them making any mistakes.

Continue reading “Number Stations Gone Wild” →

Listen To 64 MHz At Once

November 16, 2022 by 27 Comments

We imagine that if [Tech Minds] told us he was listening to the HF bands, we might ask him which one? His reply might just be “All of them.” That’s thanks to the RX-888 MKII SDR he reviewed which delivers a 64 MHz window on the radio spectrum. You can catch the video review, below.

These are not especially inexpensive, but with that bandwidth and 16-bit resolution, it is worth it if you need that kind of horsepower. There is a separate input for VHF signals 64-1700 MHz where the bandwidth is only 10 MHz, but still.

Of course, making a very wideband front end for something like this is non-trivial, so we wonder how the performance is compared to similar-priced units with less bandwidth. On the other hand, it does seem to work well enough in the video. The software used limited the test to a 32 MHz bandwidth, which is still plenty.

Speaking of software, we noticed that the developers of SatDump and SDR++ are not happy with the state of the software for the RX-888. We aren’t sure if this remains a problem, but the device seemed to work well on the video, at least.

There are many options now when it comes to higher-end SDRs. We like the Pluto for both transmitting and receiving. Of course, the RTL-SDR kind of started everything with hobby SDR, but you can’t expect that much bandwidth with one of those.

Continue reading “Listen To 64 MHz At Once” →

Getting To The Heart Of A Baofeng

November 15, 2022 by 32 Comments

In amateur radio circles, almost no single piece of equipment serves as more of a magnet for controversy than the humble Baofeng handheld transceiver. It’s understandable — the radio is a shining example of value engineering, with just enough parts to its job while staying just on the edge of FCC rules. And at about $25 a pop, the radios are cheap enough that experimentation is practically a requirement of ownership.

But stripped down as the Baofeng may be, it holds secrets inside that are even more tempting to play with than the radio itself. And who better than [HB9BLA], a guy who has a suspiciously familiar Swiss accent, to guide us through the RF module at the heart of the Baofeng, the SA818. For about $8 you can get one of these little marvels off AliExpress and have nearly all the important parts of a VHF or UHF radio — an SDR transceiver, a power amp, and all the glue logic to make it work.

In the video below, [Andreas] puts the SA818 module through its paces with the help of a board that pairs the module with a few accessories, like an audio amp and a low-pass RF filter. With a Raspberry Pi and a Python library to control the module, it’s a decent imitation of the functionality of a Baofeng. But that’s only the beginning. By adding a USB sound card to the Pi, the setup was able to get into every ham’s favorite packet radio system, APRS. There are a ton of other applications for the SA818 modules, some of which [Andreas] mentions at the end of the video. Pocket-sized repeaters, a ridiculously small EchoLink hotspot, and even an AllStar node in an Altoids tin.

Of course, if you want to get in on the fun, you’re going to need an amateur radio license. Don’t worry, it’s easy — we’ll help you get there.

Continue reading “Getting To The Heart Of A Baofeng” →

Power Up Vintage Electronics Less Unsafely With A Dim-Bulb Tester

November 13, 2022 by 54 Comments

Plugging in something like an antique radio to see if it works is a good way to have a bad time, because some old components don’t age well. For vintage electronics, inspection and repair are steps one and two. When it comes time to cautiously apply power, it’s best to use what’s called a dim-bulb tester and most hackers can probably put one together from scrap.

Being able to use one (or both) bulbs adds some flexibility, and the embedded power monitor is an inexpensive and handy addition.

These testers make it easier, and safer, to tell if there are any big problems with a device’s power supply. In its simplest form, a dim-bulb tester puts an incandescent lamp in series between a device — like an old radio — and the AC power from a wall socket. Thanks to this, if the device has a short circuit, the bulb will simply light up instead of causing any damage.

Ideally, one uses a bulb with a wattage rating that is roughly equal to the power consumption of the device being tested. If all is well, the bulb will glow very faintly and the device will work normally. A brightly glowing bulb would indicate excessive current draw. To allow some flexibility, [Doz]’s tester design allows using one or two 60 W incandescent bulbs in series, and even incorporates an inexpensive power monitor.

A dim-bulb tester isn’t an in-depth diagnostic tool but it is effective, simple, and allows for a safe startup even if there’s a serious problem like a short.  It helps protect valuable hardware from going up in smoke. In fact, the fundamental concept of limiting power to protect hardware in case of a fault has also been applied in the world of retrocomputing, where it helps protect otherwise irreplaceable hardware if something goes wrong.