Category: Digital Signals

Frugal Radio: Review of our RTL-SDR Blog L-Band Patch Antenna

Over on YouTube Rob from Frugal Radio has uploaded a video reviewing our new L-Band Patch antenna which we released for sale late last month. The patch is currently on a release sale for US$44.95 including free standard airmail shipping to most countries. We will be ending the sale this Wednesday at which point the price will go to US$49.95, still with free standard airmail shipping to most countries. The patch can be purchased from our web store at www.rtl-sdr.com/store.

In the video Rob demonstrates the patch receiving Inmarsat signals strongly, and decodes a few AERO signals using JAERO. He shows that the patch works on any RTL-SDR with bias tee capability as well as an Airspy Mini. Lastly he compares the unit against the SDR-Kits patch.

We note that we are also supplying a kit for a giveaway to Frugal Radio subscribers that we will announce in an upcoming video coming out a few days time.

RTL-SDR updated L-band patch antenna review - perfect for your SDR radio!

UPDATE: Giveaway information now available in the latest video below.

RTL-SDR L-Band Patch Antenna Giveaway

Project Horus 55: Live Video from a High Altitude Balloon

Project Horus 55 was a project that involved creating a high altitude balloon with payload that could broadcast live video down to ground station observers, as well as creating the ground station receive hardware. On March 7th 2021 the balloon was launched and ground station observers successfully received the live video.

The transmission hardware onboard the balloon was a Raspberry Pi Zero which captured and compressed the video, and a LimeSDR Mini which broadcast a DVB-S signal at 445 MHz. Power amplification was provided by an 800mW LDMOS amplifier. On the ground station side, RTL-SDRs were used as the receiving hardware and SDRAngel as the software. Although high gain auto tracking Yagi's were used by the main ground station team, it's interesting to note that the balloon chase team were also able to receive the video with a simple vechicle mounted turnstile.

In the video below Mark VK5QI who was one of the people behind the project discusses the setup before the launch.

Live Amateur TV from 100,000 feet!

The video below shows the launch and some of the live video received.

Receiving Video Directly from a SpaceX Falcon 9 Rocket + Scott Manley Video

Last week we posted about how several users on Reddit & Twitter worked together to receive and decode text telemetry from the SpaceX Falcon 9 rocket launch using a HackRF, 1.2m dish with custom 2232.2 MHz feed and GNU Radio. In that thread it was hinted that the text telemetry was only a small portion of data contained in the entire signal. It turns out that the remaining data is the SpaceX engineering video feed which is often shown in the official live coverage streams.

Over on Reddit user /u/TRGFelix writes how he was able to receive and decode the video with his own low cost setup involving an Airspy Mini SDR, TV MMDS downconverter and the ubiquitous low cost WiFi grid dish that we've often used for GOES satellite reception and for Hydrogen Line radio astronomy. The software used was the SatDump decoder created by /u/Aang253 which builds on the research done by @r2x0t:

So today at 10:21UTC i got my own recording of Falcon9 video feed downlink on S band 2272.5MHz and with u/Aang253's software SatDump i could easily decode it from the recording straight down to mxf, avi or mp4 video file! Even with very simple recieving setup!

Setup used for receiving was simple wifi grid mesh dish antenna (100x60cm) on a tripod with old MMDS TV downconvertor and Airspy MINI. here is a photo of the setup few minutes before launch But of course its doable without convertor with SDR such as HackRF , two SPF5189Z LNAs and same antenna or even TV dish with DIY S band feed!

Software used for recording was great performing opensource SDR++ by u/xX_WhatsTheGeek_Xx link here https://github.com/AlexandreRouma/SDRPlusPlusS oftware used for decoding was u/Aang253's Satdump software which i will link later as it still needs readme written and confirm it runs without bugs! UPDATE - LINK: https://github.com/altillimity/SatDump

Original MXF video together with CADU file and I/Q file recording 6MSPS int16 here. https://files.altillimity.com/Falcon%209%20OK9UWU/

TRGFelix is also on Twitter as @OK9UWU and he has posted images of his setup, and part of the video he decoded. TRGFelix notes that he is working on a tutorial which we are very eager to see!

It's extremely interesting that we can see views of the liquid oxygen floating around inside the stage two tank which is not shown during the official live streams.

As a bonus, this story was also covered by the very popular space YouTuber Scott Manley who has put out a great video popularizing the discovery and touching on a few interesting points such as how SpaceX may be legally required to encrypt these videos in the future (but hopefully not!).

How Amateur Radio Fans Decoded SpaceX's Telemetry & Engineering Video

GNU Radio Amateur Radio Meeting: A Look at Project 25 (P25) Digital Radio

Over on their YouTube channel GNU Radio have uploaded a recent talk by Aaron Rossetto titled "A Look at Project 25 (P25) Digital Radio". The talk explains the North American public safety P25 system in great depth, and is a good watch for anyone looking into details on how the system works in a deeply technical way. He later shows some examples of his P25 decoding and recording setup. Slides can be found here, and the video is posted below.

Agenda: In this presentation, I will introduce Project 25 digital radio, with a strong emphasis on its use in North American public safety trunked radio systems, and to describe experiments monitoring and decoding P25 traffic using GNU Radio code.

  • What is Project 25?
  • A brief introduction to trunked radio
  • Diving into the P25 protocol
    • Modulation
    • Packet framing and encapsulation
    • Packet types
  • GNU Radio and P25 decoding experiments

GNU Radio Amateur Radio Meeting

Receiving SpaceX Falcon 9 Telemetry with a HackRF and 1.2m Satellite Dish

Over on the Reddit /r/SpaceXLounge discussion board user /u/Xerbot has made an interesting post showing how u/derekcz was able to receive the telemetry signals from the latest SpaceX Falcon 9 rocket launch using a HackRF and a 1.2m prime focus dish with homebuilt feed designed for the 2232.5 MHz downlink frequency. Then after demodulating the signal with GNU Radio, /u/Xerbot was able to convert that signal into binary data, and then into plain text strings. 

Another user /u/Origin_of_Mind then figured out that these strings are debug messages being sent by the software-defined GPS receiver, which amongst other data contains the GPS coordinates of the second stage. The GPS data indicates that the second stage was tracking over the north of Serbia at an altitude of 219 km and velocity of 7483m/s. /u/derekcz was able to then confirm that he was indeed recording the signal when the satellite would have been crossing Serbia, confirming the received telemetry was correct.

The entire thread is an interesting read, with multiple users dissecting the plaintext and finding out information about the launch. /u/Origin_of_Mind's post in particular explains the meaning of each of the data fields, which includes the system time, the XYZ coordinates in the earth-centered earth-fixed (ECEF) coordinate system, the loss of precision due to unfavorable GPS satellite positions and the number of GPS satellites currently received.

Another user /u/softwaresaur even notes that there was an "radiation_fdir_activation_guard" event. FDIR stands for Fault Detection, Isolation and Recovery (FDIR) and this event was triggered due to 0.06 s mission time discrepancy between the rocket and GPS true time.

SpaceX Falcon 9 Telemetry Downlink Decoded

DragonOS: Decoding FT8 on Linux with WSJT-X

DragonOS is a ready to use Ubuntu Linux image that comes preinstalled with multiple SDR program. The creator of DragonOS, Aaron, uploads various YouTube tutorials showing how to use some of the preinstalled software. This month one of his tutorials covers how to use a SDRplay RSP1A or a HackRF to receive and decode FT8 with the preinstalled software WSJT-X or JS8Call. Aaron also notes that an RTL-SDR could also be used as the SDR.

In the video he covers how to set up a virtual audio cable sink in Linux for getting audio from GQRX into WSJT-X, setting up rigctld to allow WSJT-X to control GQRX, configuring GQRX, CubicSDR and WSJT-X, and finally downloading and using GridTracker.

DragonOS Focal Receive FT8 w/ WSJT-X (RSP1A, HackRF One, GQRX, CubicSDR, GridTracker)

SignalsEverywhere: Installing and Configuring OP25 Phase 1 & 2 Digital Voice Decoder on Linux

In this weeks video Sarah from the SignalsEverywhere YouTube channel show us how to install and configure the OP25 software on a Linux machine. OP25 is a Linux based P25 digital voice decoder which works with RTL-SDR dongles. It is capable of decoding both Phase 1 and Phase 2 systems. Installation is fairly simple via an installation script, but it does take some time to install. After installation Sarah shows how to configure the software in order to properly follow a trunked P25 system. In order to help with importing talkgroup information from a premium RadioReference account Sarah has also created an automatic importer Python script which is very useful.

OP25 Installation and Configuration Tutorial | Setup OP25 P25 Phase 1 and 2 SDR Decoder on Linux Pi

Hacking a Ceiling Fan Radio Control Signal with an RTL-SDR

Over on YouTube "River's Educational Channel" has uploaded a video showing how he was able to reverse engineer the wireless control signal from his ceiling fan remote, and use that information to create a new transmitter controlled via his smart home's Raspberry Pi.

In the video River uses an RTL-SDR and the Spektrum software to initially identify the remotes frequency, before moving on to record the signal in Universal Radio Hacker (URH). He then goes on to reverse engineer the signal and determine the binary control string for each button on the ceiling fan's remote control.

In part 2 which is yet to be released River will show how to transmit this signal via his Raspberry Pi 3B in order to integrate it with his smart home.

Hacking My Ceiling Fan Radio Signal With a $15 USB TV Tuner (RTL2832U)