Tagged: LRPT

r2Cloud: Software for Automatically Decoding APT/LRPT Weather Satellites and Cubesats on a Raspberry Pi with RTL-SDR

Thanks to a tweet by @rf_hacking we recently came across an interesting project called "r2cloud". This is an open source program provided on a ready to use image for the Raspberry Pi that can be used to set up an automated satellite recording station for NOAA APT and Meteor LRPT signals, as well as for CubeSats.

The software presents a web based user interface that is easy to setup and view decoded images on. It appears that the software also communicates with a public server that can aggregate and log your data, and also provide it to SatNOGS and provide FunCube satellite telemetry to FunCube Warehouse.

Block Diagram for the r2cloud software.
Block Diagram for the r2cloud software.

Meteor M2 is Currently Experiencing Orientation Issues

Russian weather satellite Meteor M2 is a popular reception target for RTL-SDR radio enthusiasts, as it allows you to receive high resolution images of the Earth. However, currently it appears to be exhibiting orientation issues, causing off center and skewed images and sometimes poor/no reception. Russian blog "aboutspacejornal", writes that the orientation of the satellite can sometimes be restored presumably by a reset command from Earth, but shortly after goes back into uncontrolled rotation.

These sorts of off-axis images were commonly received from the older decommissioned Meteor-M1 satellite, which woke up from the dead in 2015. The resurrection was speculated to be from the batteries shorting out, allowing power to directly flow from the solar panels while in full sunlight. These days Meteor-M1 is no longer transmitting.

Meteor M2 proving the curvature of the earth due to it's orientation issues.
Meteor M2 proving the curvature of the earth due to it's orientation issues.  Image source aboutspacejornal.

Hopefully Meteor-M2 can be fixed, but if not, Meteor M2-2 is due to be launched on July 5 which should also have an LRPT signal that can be received easily with an RTL-SDR. Hopefully the launch is more successful than the November 2017 launch of Meteor M2-1 which unfortunately was a complete loss as it failed to separate from the rocket.

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.

A Video Tutorial about Receiving HRPT Weather Satellite Images

Over on YouTube 'Tysonpower' has recently uploaded a very informative video and blog post showing how he is able to receive HRPT weather satellite images. Note that the video is in German, but English subtitles are provided.

Most readers of this blog are probably familiar with the more commonly received APT images that are broadcast by the NOAA satellites at 137 MHz, or perhaps the LRPT images also broadcast at 137 MHz by the Russian Meteor M2 satellite. HRPT signals are a little different and more difficult to receive as they are broadcast in the L-band at about 1.7 GHz. Receiving them requires a dish antenna (or high gain Yagi antenna), L-band dish feed, LNA and a high bandwidth SDR such as an Airspy Mini. The result is a high resolution and uncompressed image with several more color channels compared to APT and LRPT images.

In his video Tysonpower shows how he receives the signal with his 3D printed L-band feed, a 80cm offset dish antenna (or 1.2m dish antenna), two SPF5189Z based LNAs and an Airspy Mini. As L-band signals are fairly directional Tysonpower points the dish antenna manually at the satellite as it passes over. He notes that a mechanised rotator would work a lot better though. For software he uses the commercial software available directly from USA-Satcom.com.

[EN subs] HRPT - Erste Bilder! und mein Setup

An Example HRPT Image Received by Tysonpower.
An Example HRPT Image Received by Tysonpower.

A Tutorial on Receiving HRPT Weather Satellite Images with an SDRplay RSP2

RSP2user's HRPT equipment

Over on the SDRplay forums user 'RSP2user' has put up a quality post describing how he receives HRPT weather satellite images with his SDRplay RSP2. HRPT stands for 'High Resolution Picture Transmission' and provides a much higher resolution image compared to the APT weather satellite images typically downloaded from NOAA satellites. Somewhat confusingly the picture quality of HRPT is similar to LRPT (low rate picture transmission) which is used on the Russian Meteor M series weather satellite. HRPT provides 1.1 km resolution, whilst LRPT provides 1 km resolution.

Currently there are multiple satellites broadcasting HRPT signals including NOAA 19, NOAA 18, NOAA 15, Meteor M2, Fengyun 3B, Fengyun 3C, Metop A and Metop B.

The difference in difficulty of receiving APT and LRPT versus HRPT transmissions typically occur in the L-band at about 1.7 GHz, and requires a directive high gain antenna with tracking motor to track the satellite as it passes over. This makes these images many times more difficult to receive compared to APT and LRPT which only require a fixed position antenna for reception at the more forgiving 137 MHz.

Over on his post RSP2user shows how he uses a repurposed Meade Instruments telescope tracking mount and controller to drive the tracking of a 26 element loop Yagi antenna. A 0.36dB noise figure LNA modified with bias tee input is used to boost the signal and reduce the noise figure. The signal is received by a SDRplay RSP2 and processed on a PC with USA-satcoms HRPT decoder software, which is available for purchase by directly contacting him. The HRPT signal bandwidth appears to be about 2.4 MHz so possibly an RTL-SDR could also be used, but it might be pushing it to the limit.

If you are interested, RSP2user also uploaded an APT weather satellite image reception tutorial on another post. This tutorial shows how to build a quality quadrifilar helix antenna as well.

Receiving the HRPT signal on USA-Satcoms' HRPT decoder.
Receiving the HRPT signal on USA-Satcoms' HRPT decoder.

A New Meteor M LRPT Image Decoder for Windows, Linux, MacOS and Raspberry Pi

Thanks to twitter user @LinuxSocist for submitting a link to this new Meteor M weather satellite LRPT decoder called ‘meteor_decoder’ which can be run on both Linux and Windows. Pre-built binary of the software for Windows, Linux Raspberry Pi and MacOS are available at orbides.org.

This software decoder appears to be an excellent choice for those people who want to perform their reception and decoding of Meteor M satellites all in Linux. Previously as explained in this previous post, you were able to receive the QPSK data in Linux with an RTL-SDR and a GNU Radio program, but then you’d still need to boot into Windows or run Wine to run LRPTofflinedecoder in order to generate the image. Now it appears that the image generation can be performed natively in Linux too with meteor_decoder. This help with creating portable automated Raspberry Pi based Meteor M decoder servers.

Meteor M is a class of Russian weather satellites that transmit live weather images of the earth as they pass over your location. They are somewhat similar to the NOAA satellites, although the Meteor satellites transmit higher quality images via a digital LRPT signal, rather than the analog APT signals used by NOAA. With an RTL-SDR, an appropriate antenna and decoding software they can easily be received.

An Example LRPT Image Received with an RTL-SDR from the Meteor-2 M2.
An Example LRPT Image Received with an RTL-SDR from the Meteor M-N2 Satellite.

Real-Time decoding of Meteor-M2 on Linux

Recently RTL-SDR.com reader Mark wrote in and wanted to share his modified version of otti-soft’s GNU Radio flowgraph for decoding Meteor-M2 weather satellite images on Linux. The modified version allows for real time decoding, whereas the original version requires several offline decoding steps to be performed after recording the signal.

Mark writes:

I have modified one of otti-soft’s gnuradio flowgraphs so that they work with RTL-SDR and output the demodulated symbols to a TCP socket, from which the new version of LRPT Analizer (from robonuka.ru) can decode the data in real-time.

First, one needs to download and extract the AMIGOS version of the LRPT analyzer from robonuka.ru: ftp://meteor2soft:[email protected]/AMIGOS/AMIGOS2.zip.

(AFAIK, only the AMIGOS version is able to decode the data from a socket, which is required for real-time decoding).

The program is to be run under a 32-bit version of Wine.

When the satellite is overhead, open and run the flowgraph (attached) in gnuradio-companion and leave it running. You might need to adjust the gain.

Then, run the LRPToffLineDecoder.exe executable from the extracted archive.
It should display a constantly-updating constellation diagram. When the data is decoded, the channel images will start to appear in each section of the window.

That’s it, when the image is decoded, one can save it and close the windows of gnuradio-companion and the decoder.

Notes: when running the flowgraph, no other processes (rtl_sdr, rtl_power, gqrx, …) should use the SDR device.

The modified GRC file is available here.

The real-time Meteor M2 GNU Radio script for Linux
The real-time Meteor M2 GNU Radio script for Linux

Setting up an RTL-SDR based APT/Meteor Satellite Weather Station Receiver

Recently a reader of our blog, Initrd, wrote in to let us know about a new tutorial he created that shows how to set up a dual NOAA APT and Meteor LRPT weather satellite monitoring station with an RTL-SDR dongle. These weather satellites transmit a live image of the portion of the earth that they are currently over, providing a valuable tool for weather analysis. APT transmissions are analogue and are transmitted by the American NOAA satellites, and the newer Meteor M2 satellite transmits a higher resolution image in the LRPT format. We also have posted separate tutorials that show how to set up NOAA APT and Meteor M2 LRPT decoding with an RTL-SDR, but Initrd’s tutorial appears to be a good all in one guide.

His tutorial takes you step by step through a process that involves setting up the satellite tracking software Orbitron, all the required SDR# plugins, the APT decoder WXtoIMG and the LRPT decoder. The tutorial also shows how to connect them all together and set them up so that APT and LRPT decoding can coexist.

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