Tagged: rtl2832u

AERO C-Channel Voice Audio Now Decodable with JAERO

JAERO was recently updated by programmer Jonti, and it now supports the decoding of AERO C-Channels which are voice audio channels that exist on both the L-Band and C-Band frequencies of AERO. AERO is a satellite based communications service used by modern aircraft. The information transferred are normally things like aircraft telemetry, short crew messages, weather reports and flight plans. It is similar information to what is found on VHF/HF ACARS.

Jonti notes that these C-Channel voice signals are very weak as they are spot beams, so a good antenna system is required to receive them. Over on Jonti's JAERO website there is now some information about these C-Channels (scroll all the way down to the C-Channel heading and read to the end of the page), as well as a frequency list. An excerpt of the information is pasted below:

Inmarsat C and in particular AERO C channels provide circuit switched telephony services to aircraft. The channels of interest are those that carry AMBE compressed audio at a channel rate 8400 bps and voice rate of 4800bps. There is also an older speech codec still in use, LPC at a voice rate of 9600 bps and an overall channel rate of 21000bps.

Telephone channels are two-way duplex. In the from-aircraft direction transmissions are roughly in the 1646 to 1652 Mhz range. The satellite up-converts these transmissions to C band, similar to T and R channel burst transmissions. So it is possible to receive the from-aircraft transmissions although it is significantly more difficult than those in the to-aircraft direction on the L band. So for those who want to get started receiving these transmissions the L band is by far the easiest place to start.

Another aspect of the C channels is that they most often use spot beams rather than global beams which makes it more difficult to receive transmissions for aircraft using a spot beam that is aimed at another region. However if you are inside the spot beam the transmissions are relatively easily received on L band. A 60 cm dish with an LHCP helical and L band LNA will provide excellent results but even with a patch antenna it can be done.

Decoding these channels to audio in JAERO takes a little effort to setup. Due to the uncertain legal status of the digital audio AMBE codec, the codec code needs to be compiled manually first, and then placed into the JAERO directory. Jontio has uploaded the AERO AMBE codec source code at https://github.com/jontio/libaeroambe. Since JAERO is a Windows program, compilation of libaeroambe involves using MSYS2.

Once fully set up with the audio codec, the audio will come out of default soundcard set in Windows audio properties, so ensure that any Virtual Audio Cables are not set as the default device.

On the L-band link you can get conversations from the ground to the plane. The C-band link would get you the plane to ground side of the conversation too, but that is a challenging signal that would require a large dish and Jonti doesn't know of anyone who has managed to receive that before. Typically the conversation topics are things like Medlink which is a multilingual medical support line that can provide backup to doctors or aircrew handling medical emergencies in the air. In Europe the USAF also apparently use C-Channel.

AERO C-Channel Being Received with JAERO
AERO C-Channel Being Received with JAERO

UFO Detection with an Image Intensifier and FM Reflections Received with an RTL-SDR

Recently reader Syed Ali wrote in and wanted to share some experiments in UFO detection that he's been performing with an image intensifier and an RTL-SDR. The RTL-SDR is used to detect a distant FM radio station reflecting from objects passing overhead, and the image intensifier is a sensitive camera that helps make events like satellite passes more visible. In his video some visually detected objects like a possible satellite pass or aircraft at 0:09 to 0:18 and 0:55 to 1:00 seem to correlate with a radio reflection. 

Syed Ali writes:

These are three small video clips taken from an hour observation. I had an idea how to use RTL-SDR for meteor detection. So I tuned my rtl-sdr to a distant FM Radio station behind a mountain range from my own location. Any object flying over mountain range can be detected by receiving the transmission of that FM radio station via its signal being reflected from that flying object.

So I set up my image intensifier pointing towards the sky in the same direction above those ranges. I recorded a few unknown objects in the video viz a viz their RF reflections and Dopplers in sdrsharp software.

You will also notice a strange laser beam which seems to be coming from the sky to the ground because it encircles and changes its position around the field of view of my image intensifier. Moreover, in the last few seconds of the clip, you will see a strange object hovering and then taking a U turn near left edge of the video frame. Those were indeed strange findings. Please see for yourself and do leave your comments. Thanks. Observation Time : 1:20 am to 2:30 am, 21 October 2018

We're a little skeptical about the UFO claims though, as the lasers may just be car headlights, and the fast moving object may just be a bug reflecting light, and the lack of radio reflections around those points seem to confirm that nothing large is there.

UFO Detection using Image Intensifier and RTL-SDR

SDR# Update: SpyServer Network Browser now Available

The programmers of SDR# have just released a new version which now includes a SpyServer directory browser. SpyServer is an Airspy and RTL-SDR compatible SDR streaming server for SDR#. It allows you to access your SDR remotely over the internet or a network connection by using efficient data compression techniques. 

The new browser allows you to browse for active and publicly shared SDRs that are running SpyServer. To launch the browser in the latest SDR#, choose "SpyServer Network" in the Source drop down menu, and click on the "..." button. At the moment there are only a few servers listed, and not all work. But we expect more to show up and work as people update their SpyServer software.

For SpyServer users, the latest server version will automatically list your server in the directory, but it can be turned off in the config file.

SpyServer Network Browser
SpyServer Network Browser

Receiving GOES Weather Satellite Images with GNURadio and XRITDecoder in Windows

Thank you to ON7NDR as well as CM2ESP for submitting and figuring out a way to get GOES 16 decoding working with RTL-SDR using the free XRITDecoder, Xrit2Pic software and GNU Radio for Windows. 

ON7NDR's story is that he wanted to be able to receive GOES 16, but not being familiar with Linux he wanted a Windows based solution. He writes that the credit to finding the solution goes to CM2ESP who has written up a tutorial (pdf) explaining how to set everything up in Windows. ON7NDR has also written a separate complimentary tutorial (docx) that explains some steps in CM2ESPs tutorial a little further and provides a few tips on choosing correct the correct version of GNU Radio. He's also provided a screenshot showing what the correct config file looks like for an RTL-SDR dongle.

We note that for Windows there is also USA-Satcom's XRITDecoder, however this is closed source software which costs $100 USD.

GOES Full Disk Image of the Earth
GOES Full Disk Image of the Earth

A Complete Linux based Receiver and Decoder Application for Meteor M2

Thank you to Neoklis (5B4AZ) for writing in and letting us know about his recently completed project which is a RTL-SDR compatible receiver and decoder application for the Meteor M2 weather satellite. It is a combination of other open source programs and he writes:

I combined the recently released Meteor-M2 LRPT demodulator by Davide Belloli (dbdexter-dev), and the older image decoder (translated to C) released by Artem Litvinovich (artlav), with relevant code from my own "sdrx" SDR Receiver application to create a complete monolithic Meteor-M2 Receiver and Image Decoder application, "glrpt".

Neoklis' glrpt application is available on his website www.5b4az.org under the "Weather Imaging -> Meteor M LRPT Receiver" menu. The application is open source and appears to be Linux only. In order to install it you'll need to download and compile the source code, and compilation instructions are available in the documentation stored in the doc folder. Neoklis also writes that you can find his older APT image decoder called "xwxapt" under the same Weather Imaging heading of his website.

GLRPT User Interface Showing Processed Meteor M2 Images
GLRPT User Interface Showing Processed Meteor M2 Images

KerberosSDR Now Available for Pre-order on Indiegogo

We're happy to announce that KerberosSDR is now available for pre-order on Indiegogo.

As promised we announced the release to KerberosSDR mailing list subscribers first, so that they'd be the first to get the initial discounted early bird units. However due to much higher than expected interest, we have released a few "second early bird" units at a still discounted price of $115 + shipping. We're only going to release 300 of these so get in quick before the price jumps up to $125. Our pre-order campaign will last 30 days, and afterwards the retail price will become $150.

If you weren't already aware, over the past few months we've been working with the engineering team at Othernet.is to create a 4x Coherent RTL-SDR that we're calling KerberosSDR. A coherent RTL-SDR allows you to perform interesting experiments such as RF direction finding, passive radar and beam forming. In conjunction with developer Tamas Peto, we have also had developed open source demo software for the board, which allows you to test direction finding and passive radar. The open source software also provides a good DSP base for extension.

More information available on our KerberosSDR page, and the Indiegogo page.

KerberosSDR with Calibration Board Attached (Metal Enclosure with SMA connectors Not Shown)
KerberosSDR with Calibration Board Attached (Metal Enclosure with SMA connectors Not Shown)
KerberosSDR Main Board (Metal Enclosure with SMA connectors Not Shown)
KerberosSDR Main Board (Metal Enclosure with SMA connectors Not Shown)

Using an RTL-SDR to decode VOR Aircraft Navigation Beacons in Real Time

VOR stands for VHF Omnidirectional Range and is a way to help aircraft navigate by using fixed ground based beacons. The beacons are specially designed in such a way that the aircraft can use the beacon to determine a bearing towards the VOR transmitter. VOR beacons are found between 108 MHz and 117.95 MHz, and it's possible to view the raw signal in SDR#.

Over on RadioJitter author Arnav Mukhopadhyay has uploaded a post describing how to decode VOR into a bearing in real time using an RTL-SDR dongle. His post first explains how VOR works, and then goes on to show an experimental set up that he's created using a GNU Radio program.  With the software he was able to decode an accurate bearing towards the VOR transmitter at a nearby airport.

Arnavs post is a preview of an academic paper that he's worked on, and the full paper and code is available by request on the radiojitter post. We've also seen on YouTube that Arnav has uploaded a video showing the software working in action, and we have embedded it below.

Bearing to nearby airport VOR transmitter determined with an RTL-SDR and GNU Radio.
Bearing to nearby airport VOR transmitter determined with an RTL-SDR and GNU Radio.

Reverse Engineering Wireless Blinds with an RTL-SDR and Controlling them with Amazon Alexa

Amazon Alexa is a smart speaker that can be programmed to control home automation devices via voice commands. For example, Stuart Hinson wanted to be able to control his wirelessly controlled blinds simply by verbally asking Alexa to close or open them. Stuart's blinds could already be controlled via a 433 MHz remote control, so he decided to replicate the control signals on an ESP8266 with 433 MHz transmitter, and interface that with Alexa. The ESP8266 is a cheap and small WiFi capable microchip which many people are using to create IoT devices.

Fortunately replicating the signal was quite easily as all he had to do was record the signal from the remote control with his RTL-SDR, and use the Universal Radio Hacker software to determine the binary bit string and modulation details. Once he had these details, he was able to program the ESP8266 to replicate the signal and transmit it via the 433 MHz transmitter. The remaining steps were all related to setting up an HTTP interface that Alexa could interface with.

If you're interested, we've also previously posted about another Alexa + RTL-SDR mashup which allows Alexa to read out ADS-B information about aircraft flying in your vicinity.

[First seen on Hackaday]

The ESP8266 with 433 MHz Transmitter
The ESP8266 with 433 MHz Transmitter