Tagged: rtl-sdr

OrbitNight: A Free Browser-Based Satellite Pass Viewer with Antenna Rotator Control via Web Serial

Thank you to the OrbitNight team for writing in and sharing their "OrbitNight satellite radar", a free browser-based pass viewer for any satellite in the catalog. It can also point an antenna rotator straight from the browser over USB using Web Serial, so you don't need to install anything.

The radar page shows a polar plot of the pass track, live azimuth and elevation readouts, and an AOS/LOS countdown. A radio tab lists downlink and uplink frequencies taken from SatNOGS. For rotator control, it supports Yaesu GS-232 compatible controllers (including K3NG and ERC) and EasyComm II controllers like those used on SatNOGS stations connected over USB serial, or Bluetooth on Android. It also has an azimuth offset setting and a 1 degree deadband.

The site works in Chrome and Edge on desktop, and rotator control needs a browser that supports Web Serial. It's free and needs no sign-up. The team notes that there is no 450 degree or flip mode yet, and they'd like to hear from anyone who tries it with a real rotator. If you track LEO satellites with a directional antenna and an RTL-SDR, this could be a simpler option than setting up Gpredict and Hamlib. We note, however, that we couldn't find an open-source codebase.

The OrbitNight Live Tracking Page
The OrbitNight Live Tracking Page

sdrtop Update: Wi-Fi Airtime Tools, POCSAG Pager Decoder and Native Airspy R2 Support

Earlier this month we posted about sdrtop, a Rust-based SDR bench instrument that runs in a terminal and is aimed at measurement rather than listening. Viktor László (MusiThang on GitHub) has now written in again to share several updates. Viktor notes that the goal is still to "make radio signals and the measurements behind them inspectable, rather than hiding everything behind a decoded result."

The biggest additions are new Wi-Fi tools. sdrtop can now survey 2.4 GHz channels 1 to 13 and name the least busy one, inspect a single channel frame by frame at three time scales, and show a channel's airtime use second by second. These tools need 20 Msps, so you need an SDR like the HackRF. There is also a new POCSAG pager decoder written from the ITU standard without external libraries. Viktor tested it over the air by transmitting with a HackRF and PortaPack Mayhem and receiving with an Airspy R2.

The Airspy R2 is now natively supported too. Its gain staging follows the R2's Linearity and Sensitivity gain curves, and sdrtop warns you before the tuner clips. RTL-SDRs are still fully supported, and native support for the SDRplay RSP1B and Airspy HF+ Discovery is in progress. The code is open source under the GPLv3 and available on GitHub.

Some screens from sdrtop
Some screens from sdrtop

AI Disclaimer: The project's CREDITS.md file notes that Claude Code was used for implementation, architecture discussion and problem-solving.

Elektro-L3 Arrives at 14.5°W and Begins Testing L-Band LRIT and HRIT

Earlier this month we posted about the Russian Elektro-L3 geostationary weather satellite drifting west from 76°E to 14.5°W. It is replacing Elektro-L2 and could bring unencrypted L-band LRIT and HRIT imagery back to Western Europe. Now tec_msat has written in again to let us know that Elektro-L3 has arrived. It is already transmitting X-band RDAS and testing LRIT and HRIT.

tec_msat notes that the satellite was only active on C-band for a couple of days. Then, on October 26, its RDAS, xRIT, and DCP (Data Collection Platform) downlinks all went up. Elektro-L2's DCP transmission at 1697 MHz was switched off at 06:30 UTC, and L3's DCP came up at 07:02 UTC. LRIT data was being received from about 09:42 UTC. GGAK (space weather data) is still being transmitted from Elektro-L2 for now.

This is the first xRIT from 14.5°W in years, so tec_msat warns that transmissions may be sporadic for a while. It's too early to judge signal strength, but it already looks stronger than L3 did at low elevation (under 15 degrees) in its old slot.

If you're in Western Europe, now is a good time to get your dish ready. SatDump is the best software for reception and decoding, and our Discovery Dish with L-band feed and an RTL-SDR Blog V3 is a great starting point for hardware.

Elektro-L3 LRIT Image Received from 14.5°W on October 26
Elektro-L3 LRIT Image Received from 14.5°W on October 26

rxx_lora: A Lightweight rtl_fm-Style LoRa Receiver for RTL-SDR and SDRplay, No GNU Radio Required

Thank you to Przemysław Wcisło (SO5DZ) for writing and sharing rxx_lora, a command-line LoRa receiver for RTL-SDR and SDRplay RSP devices. Przemysław notes that it was designed in the spirit of rtl_fm, so there are no GNU Radio flowgraphs to build or maintain. Instead, it is a single small C binary (rtl_lora or rsp_lora, plus file_lora for saved I/Q captures). Decoded packets are printed as JSONL to stdout, so you can pipe them into other programs.

Przemysław writes:

  • It's fast. The entire receive chain (detection, sync, demodulation, FEC) runs from dozens to hundreds times real-time, depending on the PHY parameters and hardware, of course.

  • It's sensitive. I've benchmarked the binary end-to-end over AWGN, and it comes within ~1-2 dB of ideal theoretical LoRa performance. It can easily demodulate Meshtastic's MediumFast preset at -14 dB SNR. I can also vouch for this based on real-world observations. Valid decodes regularly pop up at -12 to -14 dB. I even saw a frame at -17 dB SNR, although it had a bad CRC :)

  • It's stable. It's never crashed on me, apart from when I accidentally wiggled the dongle out of the USB port ;) It should also be stable from a software quality perspective. I've put together an extensive suite of quality gates and tests, including noise tests, tests against previously recorded over-the-air captures... This should make it quite unlikely that an upcoming change will accidentally introduce a major regression.

  • It doesn't require much: librtlsdr, FFTW, a C compiler, and make. Most who have dabbled with RTL-SDRs probably won't need to install a single package on top of what they already have. Python and a few libraries are used for the tests and extra tools, but they're not required for normal operation.

The receiver implements the standard LoRa PHY, so it can be used for Meshtastic, LoRaWAN, MeshCore, APRS-over-LoRa and other LoRa signals. An included Python script also decrypts Meshtastic packets with the default or configured channel keys and prints them in a readable form.

The demodulation core is derived from the gr-lora and gr-lora_sdr GNU Radio projects. The code is open source under GPLv3 and available on GitHub. It runs on Linux, and the README says macOS "probably" works too. The SDRplay version also requires the SDRplay API. For Meshtastic reception, it covers similar ground to the GNU Radio-based Meshtastic_SDR project, which we previously posted about, but with a much smaller footprint.

rxx_lora Decoding Meshtastic Packets with an RTL-SDR
rxx_lora Decoding Meshtastic Packets with an RTL-SDR

AI Disclaimer: Przemysław notes that the sensitivity improvements came from "patient and deliberate use of strong AI tools", and the README states that the project made heavy use of AI for both coding and theoretical exploration.

DAB SDR GUI: An Open-Source DAB+ Receiver for the RTL-SDR and SDRplay

Thank you to Tomas Krajco for writing in and sharing DAB SDR GUI, a Windows program for listening to DAB+ digital radio with an RTL-SDR or SDRplay RSP. DAB+ is the digital broadcast radio standard used in much of Europe and Australia, and is transmitted in VHF Band III (174 - 240 MHz).

The program scans Band III and saves the stations it finds, then plays the selected station while showing its logo, ensemble name, and song text. It also has a 10-band equalizer with presets and a spectrum analyzer with RTA bar, FFT curve and LED bar display modes. Note that the analyzer shows the decoded audio rather than the RF spectrum, so this is a program for listening rather than signal analysis.

Decoding is handled by Tomas' own plain C DAB/DAB+ library called dab-lib, and both the library and the GUI are open source under the GPLv2 license. The latest Windows installer is v0.1.5, and older Android (RTL-SDR) and Linux AppImage (SDRplay)
builds are also available on the SourceForge files page.

DAB SDR GUI Playing a DAB+ Station
DAB SDR GUI Playing a DAB+ Station

AI Disclaimer: Recent commits to the dab-lib GitHub repo, including the port of the GUI to WinUI 3, list GitHub Copilot as a co-author.

Mobile-Whip: A Compact Battery Powered Mini-Whip Style Active HF Antenna for Handhelds and SDRs

Thank you to RTL-SDR.COM reader Ernie (NH7L), who wrote in and wanted to share news about the “Mobile-Whip” antenna, an open-source active receive antenna from GitHub user skuep.

The design is based on the well-known PA0RDT Mini-Whip, but it is built for portable use. It runs from a single 18650 lithium cell with an onboard USB charger, or from 5V USB, the 4.5V bias tee on the RTL-SDR Blog V4, or a standard 12-15V Mini-Whip bias tee. It uses an ultra-low input capacitance LTC6268 op-amp instead of a JFET, draws about 20 mA, and is only 200 mm long. That makes it small enough to mount directly on a handheld like an HF-modded UV-K5, a portable receiver, or a dongle SDR. It is designed for 100 kHz to 30 MHz, but the author says it also works reasonably well on FM and 2m.

The project is a first-revision preview with some known issues. A revision B with better VHF/UHF performance is reportedly in the works. There is no reverse-TX protection yet, so pressing PTT with it attached could destroy it. The KiCad files, simulations and JLCPCB-ready assembly files are on GitHub under the CERN-OHL-P-2.0 license. Assembled boards work out to roughly €25 each.

In two YouTube videos from a Polish ham, the Mobile-Whip is compared against a 27 MHz telescopic whip on several receivers, including the Radtel RT-950 Pro, UV-K5, ATS Mini, and Malahit DSP2. The tiny PCB antenna generally comes out ahead. On the RT-950 it even receives Polish Radio on 225 kHz longwave, which the telescopic whip could not. He does note that its high gain can overload receivers with poor front-end filtering.

The "Mobile-Whip" a PA0RDT Mini-Whip inspired portable antenna for HF
The "Mobile-Whip" a PA0RDT Mini-Whip inspired portable antenna for HF

Mayhem Mobile: Run PortaPack Mayhem Apps on a Browser or Android with an RTL-SDR or HackRF

Thank you to RocketGod, one of the developers of the Mayhem firmware for the HackRF PortaPack, for writing in and sharing the news that he has released Mayhem Mobile. It lets you plug an RTL-SDR (including the RTL-SDR Blog V4), a HackRF, or a PortaPack in HackRF mode directly into an Android phone or tablet, with no PC, Zadig, or driver installation needed. It comes as a native Android APK (direct APK download) or as a WebUSB web app that also works plug-and-play on a desktop.

Along with ports of the Mayhem receiver apps, it adds a ham radio mode with SSB, CW, AM and FM, live FT8, PSK31, RTTY and CW decoding with auto mode detection, an ADIF logbook, and DMR and P25 decoding. It also includes a full rtl_433 port with over 370 protocols, plus ADS-B, AIS, APRS, pager, ACARS, BLE, RDS and satellite decoders, a wideband sweep waterfall and raw IQ capture.

With a HackRF, it can also transmit FM voice through the phone’s microphone with CTCSS and repeater offsets, as well as RTTY, Morse, APRS, POCSAG, OOK and Flipper .sub replay, all behind a safety prompt. As always, make sure you’re licensed before transmitting.

Mayhem Mobile Screenshot
Mayhem Mobile Screenshot

RTL-SDR Running Directly on iPad without Jailbreak TestFlight Invitation

Back in June, we posted about work from Arved (DK5AV/M0KDS) that enabled RTL-SDR to run directly on iPad devices without requiring a jailbreak. Previously, RTL-SDRs couldn't run directly on any iOS device. The only workaround was to run an RTL-SDR remotely and connect to it over a network via rtl_tcp.

Arved recently received distribution entitlement from Apple, which now opens the door to submitting to the Apple App Store. However, Arved notes that he would like feedback from Beta testers before that happens, so he has shared a TestFlight link at https://testflight.apple.com/join/jUDtSBmb. 

We note that this currently will only work on iPad devices with a modern M-series chip. iPhones are not compatible because they use the A-series.

Arved also writes:

The host app also contains a few more features compared to last time. It has a diagnostics view to see if the driver talks to the SDR correctly. It also contains a built-in FM receiver (including stereo and RDS) for broadcast FM stations. But finally the most important feature on the iPad is probably the built in rtl_tcp Server which runs directly on the iPad itself. That way users can use any compatible rtl_tcp client already available on iOS with this driver. Examples would be CoronaSDR, VibeSDR etc.

In the driver I also added support for the V4 dongle (which didn’t work last time). Unfortunately I had to drop the FCxxxx tuners for now due to issues with the AppStore and its GPL license issues. The whole driver is now based on the open source GNURadio driver instead of librtlsdr due to licensing issues with the GPL. Maybe I can find a way to add the other tuners back at some point. The driver for the iPad is open source (same repo as last time). The API for this driver is also available as header so that other apps in the future can directly talk to this driver.

RTL-SDR Running Directly on iPad via USB — Demo with CoronaSDR, welle.io, SatDump & rtl_tcp (no JB)