Category: Satellite

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

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

A Step by Step Tutorial to Receiving GOES-16 Images with an RTL-SDR, Raspberry Pi and Goestools

Aleksey Smolenchuk (lxe) has recently uploaded a step-by-step guide to setting up a GOES weather satellite receiver with an RTL-SDR dongle, Raspberry Pi and the goestools software.  GOES 15/16/17 are geosynchronous weather satellites that beam high resolution weather  images and data. In particular they send beautiful 'full disk' images which show one side of the entire earth. Compared to the more familiar and easier to receive low earth orbit satellites such as NOAA APT and Meteor M2 LRPT, the geosynchronous GOES satellites require slightly more effort as you need to set up a dish antenna, use a special LNA, and install Linux software.

Aleksey's tutorial first shows where to purchase the required hardware and notes that the total cost of the system is around $185. Next he goes on to show the hardware connection order, and then how to install and configure the goestools decoding software onto a Raspberry Pi.

Aleksey's RTL-SDR Based GOES Receiver setup
Aleksey's RTL-SDR Based GOES Receiver setup

YouTube Video Demonstrates GOES Weather Satellite Reception

On The Thought Emporium YouTube channel a new video has been uploaded showing the full disk images of the earth that they've been able to receive from GOES geosynchronous weather satellites. Over the past couple of years GOES satellite reception has become much easier for hobbyists to achieve with the release of the NooElec SAWbird LNA+Filter, information on how to use a cheap 2.4 GHz WiFi grid antenna for reception and the release of free open source decoder software. It was also shown that an RTL-SDR dongle is sufficient for receiving these images as well. With all these new developments it is now possible to build a GOES receiving station for under $100.

The Thought Emporium video blurb reads:

In the fall of 2016 I saw my first rocket launch and little did I know that the satellite on that rocket would come to shape and fill my thoughts for many years. We're no strangers to getting data out of space on this channel, but GOES-16 is special, and not just because I was there when it left earth. Unlike the satellites we looked at in the past, GOES is in geostationary orbit and has an amazing suite of cameras and sensors on board. While it's a bit harder to receive data from GOES the extra effort is absolutely worth it, especially because it can see then entire globe all at once and send out those images in stunning high resolution. And it even comes with the added bonus of rebroadcast data from other satellites giving us a view of the opposite side of the planet as well.

In this video we go through the hardware and software needed to receive these gorgeous images and what is contained in the signals we receive.

Pulling Clear Images Directly Off Satellites | GOES-15,16,17 and Himawari 8 HRIT

SegDSP: Distributed Cloud Based SDR with SpyServer

Over the last few months Lucas Teske (author of the Open Satellite Project) has been working on a piece of software called "SegDSP". The idea appears to create a web GUI based SDR receiver for SpyServer streams which can be used to create a cloud of channel demodulators, essentially segmenting the DSP computation burden over multiple computers.

SpyServer is a SDR server application that is compatible with Airspy products and RTL-SDRs. It allows you to connect to these SDRs remotely over a network or internet connection. The SDR server computer sends the radio IQ data over the network allowing you to perform processing remotely. A major advantage of SpyServer compared to other SDR server applications is that it only sends the raw IQ data for the portion of the spectrum that you're interested in which can save a lot of bandwidth.

One key application that Lucas envisions for SegDSP is using it with cloud clusters of single board computers (SBC) like the Raspberry Pi 3. The philosophy is that there will be specific roles for each SBC machine. For example you might have some SDR machines running SpyServers, some processing machines for demodulating and decoding multiple channels, and a storage machine for recording data. Then you can dynamically spawn / despawn workers when needed (for example only spawning a machine when a LEO satellite with data to decode passes over).

SegDSP development is still in the early stages, and appears to only have the web GUI set up at the moment with a few demodulators. But keep an eye on his Twitter @lucasteske for updates too. Lucas also did a talk at the last CyberSpectrum meetup. His talk can be found at 1:30:00 in the recording.

SegDSP Screenshot Demodulating WBFM
SegDSP Screenshot Demodulating WBFM

 

SDR# Inmarsat Decoder Plugin Now Available

Microp11, the programmer of Scytale-C a standalone Inmarsat decoder has just released a new Inmarsat decoder SDR# plugin. The plugin is currently in the "pre-alpha" stages, so is still missing some functionality and may be buggy. However, it does appear to be functional at this point in time. It can be used with RTL-SDRs, and any other SDR# compatible SDR including units running on remote SpyServers. Microp11 writes:

  • I ran it with SDR# version v1.0.0.1761.
  • If it crashes you SDR# I apologize in advance.
  • The auto-tracking (default on) will alter your SDR# frequency and follow the signal’s CF. When the SNR is very low, please disable it and manually tune the SDR# to try to get the CF as close to 2000 as possible.The demodulator still has plenty ideas of its own.
  • Use USB mode with 4000 Hz bandwidth.
  • For now the interface is missing the usual scatter plots.
  • UDP Address and UDP Port are for sending the decoded frames to the Scytale-C UI.
  • Offset and CF are the difference from zero error and the CF frequency of the demodulated BPSK signal.
  • Tx and SYM are the transmitted over UDP frames and SYM is showing the number of demodulated symbols.
  • A bunch of libraries are attached as extra files. Please be gentle and accept the package as it. Will clean-up in the future.
  • Use in conjunction with the Scytale-C UI from the archive: “x64-UI1.6-Decoder1.4.zip” (link below)
  • The magic line is included in the archive: “SDRSharp.ScytaleC-1.0-alpha.zip”

The files can be downloaded from https://bitbucket.org/scytalec/scytalec/downloads.

SDRSharp Scytale-C Plugin
SDRSharp Scytale-C Plugin