KrakenSDR is our 5-channel coherent software-defined radio designed for applications such as radio direction finding. It was successfully crowdfunded on Crowdsupply back in 2021. We've recently come across a 2025 paper in the Journal of the Institute of Navigation, describing how KrakenSDR was successfully tested as a real-world GNSS jammer and spoofer localizer.
Global Navigation Satellite System (GNSS) services such as GPS are easily jammed by hostile terrestrial signals due to their low transmit power. Jamming is commonly used in modern conflict environments, and is seen heavily in use around Ukraine, Russia, and the Middle East. Similarly, spoofing, which is transmitting a fake GNSS signal to trick receivers into seeing fake locations, is also in use.
In their paper, Lasse Lehmann et al. from the Technical University of Denmark demonstrate the use of a KrakenSDR for detecting GPS L1 jammers at 1575.42 MHz. The tests were performed at Jammertest 2023, an annual event for open GNSS experiments, and they were able to locate a spoofer down to 18.1 meters via a vehicle-mounted KrakenSDR .
Thank you to Cees for writing in and sharing his Android app, "Carshepherd," which is currently in the pre-release stage. Carshepherd works with a connected RTL-SDR and TETRA antenna to give drivers early awareness of nearby emergency-service activity (such as police, ambulance, fire) by detecting the TETRA uplink signal.
Cees notes that this is essentially the same as what hardware devices like 'Target Blu Eye' do to detect emergency services. Laser/radar detectors are illegal in most European countries, and while not advertised as such for legal reasons, Carshepherd could be a legal alternative for detecting laser/radar speed traps, detecting ProViDa video-based pacing vehicles, or just for general awareness.
The app works by continuously sweeping the TETRA bands, looking for the signature of a TETRA carrier. Once it detects a confirmed uplink carrier, it estimates proximity, which then triggers a readout and audible alert. The TETRA uplink is not always active, but emergency service vehicles often send bursts of uplink data every few seconds with GPS position updates, and, of course, during voice PTT.
The algorithm is based on a large labeled dataset from dozens of real-world test drives. The dataset trains an AI classifier that can even tell you whether an emergency unit is keeping pace with you (e.g., traveling down the same stretch of motorway as you) or whether you are approaching a stationary unit.
Carshepherd currently only works in countries whose emergency services use the TETRA communications protocol, which includes most of Europe and various other countries, but notably not the USA. However, Cees notes that they are working on a US version that will listen to the P25 network.
While Carshepherd has not yet been released, the pricing is indicated as €3.99 per month. You can sign up for the waitlist at www.carshepherd.nl.
Based on calculations of the distribution of visible stellar mass in our galaxy, a certain galactic rotational velocity-versus-distance-from-the-center curve is expected. However, when scientists actually measure the galactic rotation, another curve is found - a curve which should result in the galaxy flying apart. This mismatch in expected vs measured data has given rise to the theory of "dark matter". The theory essentially states that to produce the measured curve, the galaxy must have more mass, and that this mass must come from non-luminous matter scattered throughout the galaxy, which is difficult or impossible to observe.
In his experiment, David uses a DIY radio telescope to measure the speed of the Milky Way's rotation at various galactic longitudes via Hydrogen line Doppler-shift analysis. After plotting the results, David confirmed that his results match professional astronomers' observations.
If you're interested, we posted about a similar experiment by Job Geheniau back in 2020.
We also want to note that we sell a ready-to-use kit called the Discovery Dish, which, with the Hydrogen Line feed, could be used for this experiment.
Thank you to Muayyad for sharing news about the release of his iPad/iPhone-compatible application, 'DXLens', designed for listening to remote shortwave SDR receivers. DXLens also comes with features like aggregated shortwave schedules from multiple sources, and propagation data and reception forecasting to help users choose the right global receiver for the conditions. He writes:
DXLens is a newly released iPhone/iPad application built around connecting the shortwave schedule and SDR listening workflows.
A listener can begin with a broadcast from EiBi, Aoki/NDXC, or HFCC, inspect the schedule-source evidence and transmission path, review modeled propagation context and assumptions, and then request compatible public SDR receivers for the frequency.
From there, DXLens provides a native listening workspace with live spectrum and waterfall, frequency/mode/bandwidth controls, receiver switching and reconnection, SDR presets, signal/session information, and local recording.
The app also includes Path Atlas, ionospheric and space-weather context, RF Environment tools, Model Audit, alerts, Custom listening views, and a structured reception logbook.
An important design boundary is that scheduled activity, propagation modeling, public receiver availability, and actual reception are kept separate rather than being presented as equivalent evidence.
The app appears to connect to the KiwiSDR network, and also has support for personal rtl_tcp based receivers.
At the moment, the app appears to be free, with no in-app purchases. DXLens is available on the Apple App Store.
We're happy to announce that the RTL-SDR Blog V4L (Lite) model is now available for purchase in our store! Our initial production batches are small, so we will have limited stock at first, and the first batches will be available for shipment only from our warehouse in China. But we expect to ramp up production and get stock on Amazon over the next 2-3 months.
Currently, only our blog store (via the red add to cart button), official eBay listing and Aliexpress listing sell this product. Amazon will be stocked in about 2-3 months.
The RTL-SDR Blog V4L (Lite)
As you may already know, the Blog V4 line of products was recently made end-of-life due to the exhaustion of the stockpile of Rafael R828D tuner chips that the V4 models require. The R828D chip has not been in production for many years, but we were able to access a large stockpile of the chip via our contract manufacturer relatively cheaply, which made the Blog V4 models cost-viable. We predicted that the V4 models would be in production until the end of 2026, as we expected to be able to purchase a few more R828D chips from third-party stockpiles at slightly higher prices. But it turns out that the last few chips available in those third-party stockpiles were all counterfeits (they had put legitimate chips in the first 100 spaces in the reel, then for the rest they had lasered the R828D logo on a totally different chip with the same package size and expected us not to notice!).
We have recently secured a confirmed good stockpile of Rafael R828S chips via our contract manufacturer, which allows us to produce the new Blog V4L (Lite) design. Compared to the R828D, the R828S is a variant with one fewer RF input. This means that instead of a triplexed filtered input, we can only do a diplexed filtered input. Hence the 'lite' designator, as the design is identical to the original V4 models, except for the triplexed input filtering feature. This lack of filtering comes with a minor upside: improved sensitivity due to less filtering losses on the front end.
MDS Measurement Comparisons
Of course, the downside is that the front end is not as well filtered against strong signals, so the two-tone test produces identical results to the V3 model.
Two-Tone Test Results
The V4L still maintains the same built-in HF upconverter architecture of the V4 models and, like the V4, has the improved PCB layout, 1PPM TCXO, 4.5V Bias Tee, bias tee LED, improved power supply, and more.
Another upside is that the R828S chip is cheaper, and so we can sell the Blog V4L at a slightly lower price!
We note that, like the V4 models, the V4L is also a limited edition product. The V4L also relies on a large stockpile of a chip that is no longer in production. We expect the V4L chip stockpile to last about one year. Beyond that, we have a solid idea for V5 model design that is still in the early stages of development, but please don't expect any further news on that until 2027.
As the R828S chip has not been used in an RTL-SDR model before, the official Osmocom drivers do not yet support it. We have submitted a patch request through their channels, but have not heard back yet. - Update: Osmocom has updated their repo and added V4L support.
For now, V4L users can use our rtlsdrblog/rtl-sdr-blog driver fork available on GitHub, with Windows DLL Releases. ExtIO users can access a compatible Windows ExtIO here. We have submitted patches for the Android RTL-TCP app as well. More information about driver compatibility can be found in the V4L user's guide.
Back in September 2025, we posted about the "ESP32 Bus Pirate" firmware, which transforms an ESP32-S3 into a multi-protocol debugging and hacking tool. We later covered an update in March 2026 that added waterfall displays, cellular modem support, and an external radio expander.
Although the ESP32 does not have true SDR capabilities, it can leverage its numerous built-in radio hardware components to achieve a range of interesting SDR-like features. Recently, "Geo," the creator of the ESP32 Bus Pirate, wrote in to share some recent firmware updates with us.
Geo notes that the project is now called "ESP32 Bit Pirate" and now includes LoRa/SX1262 support and Meshtastic analysis features.
ESP32 Bit Pirate can now transmit and receive LoRa packets, monitor RSSI, scan frequency activity, display a simple waterfall view and perform Channel Activity Detection. Radio parameters including frequency, bandwidth, spreading factor, coding rate, transmit power, preamble and sync word can be configured directly from the interface.
Packets can also be recorded to the ESP32 filesystem and replayed later together with their original radio configuration.
A dedicated Meshtastic analysis shell has also been added, allowing users to send, receive and inspect Meshtastic packets. The goal is not to replace a Meshtastic node, but to provide a debugging and experimentation interface for understanding and interacting with LoRa/Meshtastic traffic.
The latest update has also added new LoRa hardware support for the Heltec Vision Master T190 and Heltec WiFi LoRa 32 V4, a browser-based debugging ecosystem, a Python scripting lab, and a BPIO2 USB adapter mode.
The project is entirely open source, and the code can be found on their GitHub page.
Thank you to Esteban Benito (EA8DGL) for writing in and sharing news of a bare-metal open source firmware for the GD32F450-based DeepSDR 101. The firmware is a collaborative effort developed by Esteban Benito (EA8DGL), Alexandr (UA6YKK), and Blas (EA7GIB). The DeepSDR 101 is a popular low-cost hand-held SDR, covering 100 kHz to 149 MHz, with a bandwidth of 192 kHZ, and a 4.3-inch screen. Various clones of the DeepSDR 101 also appear on marketplaces.
Esteban notes that the motivation for writing custom firmware was that the DeepSDR 101 and its clones have had only one firmware update since it came out. While the stock firmware currently works well, it lacks certain features such as selectable filter bandwidths and some demodulation modes, and it needs an updated interface.
Esteban writes:
The idea was to take genuinely inexpensive hardware - a GD32F450 microcontroller, an 800x480 touchscreen, a TLV320AIC3204 audio codec used as the I/Q front-end, and an MS5351 (Si5351-compatible) local oscillator - and turn it into a receiver with features you'd normally only find on much pricier radios:
- A real-time spectrum/waterfall panadapter with adjustable zoom (1x-8x), smoothing, and trace styles - AM, USB, LSB, NFM and WFM demodulation, with adjustable channel bandwidth and squelch - One-tap band presets (shortwave, airband, 2m, HF ham bands, FM broadcast, CB, and more), each pre-loaded with the right mode and tuning step - A touchscreen settings menu with configurable AGC profiles, PGA gain, backlight, and more - Encoder-based tuning down to 100Hz steps across 4.8-180MHz
Everything is bare-metal C - no RTOS, direct register access for clocks/DMA/I2S - and the whole firmware, from the I2S/audio bring-up to the DSP chain to the UI,
With this being fully open, it also opens the door to things like CW, RTTY, SSTV, HF FAX or FT8 decoding down the line - none of that requires new hardware, just firmware that's actually open enough to build on.
So really, the goal isn't to replace or criticize the original firmware - it's to give the community a base to build on, so one of the most affordable and easy-to-use SDR radios out there can keep getting better over time instead of staying frozen after a single update.
DeepSDR 101 Open Source Custom Firmware
AI-Disclaimer: We point out that Esteban discloses that this firmware is primarily being written with AI.
Thank you to Kevin Murphy (ZL1UJG) (aka Tech-ni-shn) for writing in and submitting some RTL-SDR and Airspy sensitivity measurements that he has recently done over on his YouT ube channel. In his tests, Kevin measures an RTL-SDR Blog V4, RTL-SDR Blog V3 + SpyVerter, Airspy HF+ Discovery, and Airspy Mini using a signal generator, attenuators, and SDR#.
His results show that the RTL-SDRs and Airspy devices have very similar minimum discernible signal (MDS) levels, all measured around ~-133 dBm. Kevin has provided a PDF summary of his results, and the video below.
