Antenna Mount Designed For On-The-Go SDR

December 16, 2022 by Bryan Cockfield 15 Comments

Software-defined radio is all the rage these days, and for good reason. It eliminates or drastically reduces the amount of otherwise pricey equipment needed to transmit or even just receive, and can pack many more features than most affordable radio setups otherwise would have. It also makes it possible to go mobile much more easily. [Rostislav Persion] uses a laptop for on-the-go SDR activities, and designed this 3D printed antenna mount to make his radio adventures much easier.

The antenna mount is a small 3D printed enclosure for his NESDR Smart Dongle with a wide base to attach to the back of his laptop lid with Velcro so it can easily be removed or attached. This allows him to run a single USB cable to the dongle and have it oriented properly for maximum antenna effectiveness without something cumbersome like a dedicated antenna stand. [Rostislav] even modeled the entire assembly so that he could run a stress analysis on it, and from that data ended up filling it with epoxy to ensure maximum lifespan with minimal wear on the components.

We definitely appreciate the simple and clean build which allows easy access to HF and higher frequencies while mobile, especially since the 3D modeling takes it a step beyond simply printing a 3D accessory and hoping for the best. There’s even an improved version on his site here. To go even one step further, though, we’ve seen the antennas themselves get designed and then 3D printed directly.

How On-Frequency Are Those Cheap Radar Modules?

December 6, 2022 by Jenny List 8 Comments

If you’re partial to browsing AliExpress, Banggood, or eBay for unusual hardware, you may have seen the HB100 Doppler Radar modules. These are a PCB with a metal can on board, and their reverse side has a patch antenna array. They work on a frequency of 10.525 GHz, and [OH2FTG] has characterized a few of them to see how close they lie to that figure.

These devices have a superficially very simple circuit that makes extensive use of PCB layout for creating microwave inductors, capacitors, and tuned circuits. There’s a FET oscillator and a diode mixer, and a dielectric resonator coupling the output and input inductors of the FET. This component provides the frequency stability, but its exact frequency depends on what lies within its electric field. Thus the screening can does more than screening, and has a significant effect on the frequency and stability of the oscillator.

The higher quality HB100s have a small tuning screw in the top of the can which in turn adjusts the frequency. This should be tweaked in the factory onto the correct point, but is frequently absent in the cheaper examples. In this case he has a pile of modules, and while surprisingly some are pretty close there are outliers that lie a significant distance away.

If you use an HB100 then the chances are nobody will ever bother you if it’s off-frequency, as its power output is tiny. But it’s worth knowing about their inner workings and also how to adjust them should you ever need to. Meanwhile if you’re interested in Doppler radar, here’s how to design one for a lower frequency.

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This Standalone Camera Gets The Picture Through With SSTV

November 20, 2022 by Dan Maloney 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 Arya Voronova 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 Joseph Long 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.

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Number Stations Gone Wild

November 17, 2022 by Al Williams 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.

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Listen To 64 MHz At Once

November 16, 2022 by Al Williams 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.

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