Category: Satellite

New GNU Radio Block for Decoding Meteor M2 Images

Thank you to Reiichiro Nakano for submitting news about his work on converting the Pascal based meteor_decoder software into a C++ GNU Radio block. meteor_decoder is a decoder for the Meteor M2 weather image satellite. Meteor M2 is a Russian weather satellite that transmits images down in the digital LRPT format. This provides much higher resolution images compared to the NOAA APT signals. With an RTL-SDR, appropriate satellite antenna and decoding software it is possible to receive these images.

Reiichiro works for Infostellar, which appears to be a Japanese company aiming to connect satellites to the internet via distributed and shared ground stations. It appears to be somewhat similar to the SatNOGs project. Reiichiro writes:

Just wanted to share a simple project I built for my company Infostellar, in the past week. I converted https://github.com/artlav/meteor_decoder to C++ and placed it within a GNURadio block for direct decoding of Meteor M2 images. It's a sink that expects soft QPSK demodulated signed bytes. Once the flowgraph stops running, it parses out received packets and dumps the received Meteor images in a specified location. 

The block is part of our Starcoder repository and can be installed from here (https://github.com/infostellarinc/starcoder/blob/master/gr-starcoder/lib/meteor_decoder_sink_impl.cc ).

Building A Giant $200 3D Corner Reflector Antenna for GOES, Moon Bounce and Pulsar Detection

A corner reflector antenna is basically a monopole antenna with a metallic 'corner' reflector placed behind it. The reflector helps the monopole collect signals over a wider aperture resulting in signals coming in stronger from the direction that the corner is pointing at. In past posts we've seen a homemade tinfoil corner reflector used to improve reception of the generic stock RTL-SDR monopole antenna, and a larger one was used in a radio astronomy experiment to detect a pulsar with an RTL-SDR.

Recently The Thought Emporium YouTube channel has uploaded a video showing how to build a large 2 meter 3D corner reflector out of readily available metal conduit pipes and chicken wire. While the antenna has not been tested yet, they hope to be able to use it to receive weather satellite images from GOES-16, to receive moon bounce signals, to map the Hydrogen line and to detect pulsars. 

Notice: WXtoImg Website Down

Just a note that the website for the popular NOAA APT weather satellite decoding software WxtoImg is currently down, and may possibly never be revived. This software is commonly used with RTL-SDR dongles to download weather satellite images from the NOAA 15, 18 and 19 polar orbiting satellites.

It seems that the author of the software has not been maintaining the site and software for a while, although there was a brief update on the site back in 2017 when the professional version keys were released for free. But the keys reportedly no longer work. WXtoImg is closed source, so the code is not available either.

Some of the downloads are still available via archive.org, however it only seems to be the Windows and some of the Linux versions that were archived. Over on two Reddit threads [1] [2], some users are also collecting the last free versions and making them available for download again. If anyone has access to the last beta versions for ARM devices please upload them somewhere too.

Also if anyone happens to have the contact details of the author, or someone who knows the author please let us know as we'd like to ask for permission to mirror the files.

Decoding 12 AERO Channels Simultaneously with an Airspy, Outernet Patch Antenna and SDR-Console V3

In a post uploaded last month we noted that Outernet was selling off some of their old L-Band satellite antennas cheaply. Nils Schiffhauser (DK8OK) decided to take advantage of the sale and bought one. Now Nils has created a blog post that shows how he's been able able to decode 12 L-Band AERO channels simultaneously with the Outernet L-band antenna, an Airspy R2 and SDR-Console V3. AERO is the satellite based version of aircraft ACARS, and it's L-band signals contain short ground to air messages like weather reports and flight plans. Multiple channels are often in use at any one time.

To achieve this Nils uses the multi-channel tuning capabilities of SDR-Console V3, which allows him to open up 12-channels, each tuned to a different AERO frequency. He then opens up 12 instances of the AERO decoder known as JAERO, and then uses VB-Cable to pipe the audio from each channel into a JAERO instance. Nils writes that the key to making JAERO run with multiple instances is to install JAERO into different folders on your PC, and give each JAERO.exe a unique file name like JAERO_1.exe.

He collects all the data into a program called Display Launcher and Nils notes that the whole set up has been stable digesting 54,000 messages over the last 24 hours. 

12x JAERO Decoders Running
12x JAERO Decoders Running

A Lightweight Meteor M2 Demodulator

Over on GitHub dbdexter-dev has released a new lightweight and open source Meteor M2 demodulator. Meteor M2 is a Russian weather satellite that transmits images down in the digital LRPT format. This provides much higher resolution images compared to the NOAA APT signals. With an RTL-SDR, appropriate satellite antenna and decoding software it is possible to receive these images.

This new lightweight demodulator may be especially useful for single board PCs like the Raspberry Pi. Previously, on Linux GNU Radio based demodulators have been used, and GNU Radio isn't exactly a light weight piece of software. To use the software you first need to record an IQ file of the Meteor M2 LRPT signal, downsample the IQ file to 140 kHz (if required), then pass it into the demodulator. This will spit out an 8-bit soft-QPSK file which can be used with LRPTofflinedecoder (now known as M2_LRPT_Decoder) on Windows or meteor_decoder on Linux to generate an image.

An Example LRPT Image Received with an RTL-SDR from the Meteor-2 M2.
An Example LRPT Image Received with an RTL-SDR from Meteor-2 M2.

Chasing Cubesats on a $25 Budget with an RTL-SDR and Homemade Antenna

Cubesats are small shoebox sized satellites that are usually designed by universities or amateur radio organizations for basic space experiments or amateur radio communications. Typically they have an orbit lifespan of only 3-6 months.

Cubesats typically transmit signals at around 435 MHz, and they are powerful enough to be received with a simple home made antenna and an RTL-SDR. To help with this Thomas N1SPY has created a YouTube video where he shows exactly how to construct a cheap eggbeater antenna made out of a few pieces of copper wire and an SO-239 UHF connector. Later in the video he demonstrates some Cubesats being received with his antenna, an RTL-SDR and the SDR-Console V3 software.

2018: Thomas N1SPY chases mini satellites on a budget

Video Demonstrating C-Band AERO Aircraft Tracking

AERO is essentially the satellite based version of aircraft ACARS. AERO's L-band signals contains short ground to air messages with things like weather reports and flight plans. The C-band signals are the air to ground portion of AERO and more difficult to receive as they require an LNB and large dish. However they are much more interesting as they contain flight position data, like ADS-B.

Over on YouTube Tomasz Haddad has uploaded a video of C-band AERO being received from the Inmarsat 3 F2 (Atlantic Ocean Region – East (AOR-E) 15W satellite. He uses a 1.80m motorized satellite dish with Kaonsat KS-N201G C-band LNB, a Prof 7301 PCI satellite card (to power the LNB) and an RTL-SDR V3. The C-band LNB translates the high C-band frequencies down to L-band which is receivable with an RTL-SDR. He notes that the LNB drifts quite a lot as it is not frequency stabilized.

With the signals received by his setup he's able to use the JAERO decoding software together with Virtual Radar Server to plot aircraft positional data using Virtual Radar Server. The plotted aircraft are mostly all in the middle of the ocean or in remote areas, which is where C-band AERO is normally used due to the lack of ground ADS-B stations.

Inmarsat 3 F2 15W C Band AERO Reception Using Jaero And Virtual Radar

Outernet’s Old Antenna Stock for Sale: L-Band Active and Filtered Ceramic Patch Antennas

In the past the Outernet project operated on L-band frequencies, and for the service they manufactured a number of active L-band active ceramic patch antennas for use with RTL-SDR dongles. Outernet has since moved on to faster Ku-band delivery, and hence their old L-band antennas can no longer be used for their service.  There are a few of these patch antennas left over in Outernet's stock and they are currently selling them on eBay for US $29 + shipping (link expired).

Although no longer useful for Outernet, these antennas are still very useful for receiving other L-band services such as STD-C SafetyNET and AERO. SafetyNET is a text broadcast intended for sailors at sea, but contains many interesting and potentially useful messages for others too. Often they transmit data like military sea live firing warnings, reports of marine pirate activity, search and rescue reports, scientific vessel reports as well as weather reports. AERO is the satellite version of ACARS, and is used by aircraft to communicate with text messages to and from ground stations. L-Band AERO signals only contain information from the ground station up to the aircraft. For air to ground you'll need a C-band receiver set up. AERO is the satellite communications protocol that was so heavily centered on during the MH370 flight disappearance investigation.

In the past we've reviewed the Outernet L-band ceramic patch and found it to work very well. Certainly STD-C and AERO signals are easy to receive with the antenna if you point it at the satellite. The antenna requires bias tee power and can easily be used in combination with the bias tee on our RTL-SDR V3 dongles. The onboard filter helps reduce problems from interfering signals, but restricts reception to 1525 - 1559 MHz, so Iridium signals cannot be received with this antenna.

The L-Band Active Ceramic Patch Antenna.
The L-Band Active and Filtered Ceramic Patch Antenna.