In December of last year we posted about a video demonstrating the many features that the SDRAngel software comes standard with. Recently they've added a new feature which are 3D maps that can be used to visualize signal data.
In the latest video demonstration they show these 3D maps projecting NOAA weather satellite images onto a 3D globe and at the same time tracking the NOAA satellites over the globe as it produces imagery. They also show the software visualizing a 3D model of aircraft on the globe, using live ADS-B data to show aircraft maneuvers when taking off, cruising and landing. With multiple SDRs they also show how the visualization can be combined with air traffic voice. Finally they also show marine vessels being visualized via live AIS data. There appear to be a wide range of vessel 3D models implemented.
Recently on Twitter @arvedviehweger (Arved) has tweeted that he has successfully received images from the Russian Arctic monitoring satellite known as ARKTIKA-M1, via it's X-band downlink at 7865 MHz. We've reached out to Arved and he's provided the following information on his setup and how he's receiving and decoding the images.
My first good picture from the ARKTIKA-M1 satellite on 7865 MHz!
It appears that the satellite downlink is a lot stronger now which allows me to finally get a clean decode. I really hope it will stay that way! pic.twitter.com/qy7HDA2uAP
The Arktika-M1 satellite is a Russian weather satellite which operates in a HEO orbit. It was launched in February 2021 and has downlinks on multiple bands. The main payload downlink for the imagery is on 7865 MHz (which is also known as the lower X-Band). The satellite only transmits imagery on the X-Band at the moment, it is currently unknown whether it will ever transmit any image data on L-Band.
For Amateur reception that means having access to X-Band RF gear. It usually consists of a low noise pre-amplifier and a downconverter to convert 7865 MHz down to a lower frequency for easier reception with a high bandwidth SDR such as the LimeSDR, a USRP etc.
In my personal setup I use a surplus pre-amplifier made by MITEQ (around 36dB of gain, 1dB NF), my own self-made DK5AV compact X-Band downconverter and a LimeSDR-USB.
My L-Band gear is now mounted on top of my X-Band gear which allows me to do both at the same time 🙂 I will probably try that on FY3B in the future. pic.twitter.com/SFdy04EwuT
— Arved - DK5AV/MØKDS (@arvedviehweger) July 27, 2021
The L-Band gear is mounted on top (helix and the pre-amp behind it) and the X-Band gear is right below. From left to right you can see the feed, the downconverter (silver box) and the LNA (mounted to a heatsink and a fan). Recording is done with a LimeSDR-USB running at a sample rate of 50 MSPS. The satellite transmits every 15 minutes once it reaches its apogee, each transmission including the idle period lasts for about 10 minutes. Some pictures of the idle transmission and the actual data transmission can be found in this Tweet, [noting that Idle = more spikes, actual data looks weaker]:
Depending on the geographical location a rather large satellite dish is also required for Arktika-M1. Reception reports all over Europe clearly show that the satellite has a beamed antenna (similar to ELEKTRO-L2).
In my setup I can get away with a 2.4m prime focus dish (made by Channel Master) in North Eastern Germany. It produces around 9 - 10 dB of SNR in the demod of @aang254’s excellent SatDump software. Anything above 5dB will usually result in a decode but since the satellite does not have any FEC you will need more than that for a clean picture. (Image of SNR in Satdump)
Over on his blog Derek (OK9SGC) has recently uploaded a very comprehensive beginners guide to receiving HRPT weather satellite images. HRPT reception can be a little daunting as it requires a good L-Band dish setup which involves choosing and building a feed, and importantly, a way to track the satellite with the dish as it moves across the sky. Tracking can be achieved manually by hand, but that can be very difficult and so a motorized tracking mount is recommended.
This is unlike the much easier to receive NOAA APT or Meteor LRPT satellite signals in the VHF band which can be received by a V-dipole antenna, or the geostationary GOES HRIT satellites that can be received with a WiFi grid dish and LNA. Both of which do not require tracking.
The advantage of HRPT however, is that you end up with high resolution, close-up, and uncompressed images of the earth. For example Derek notes that NOAA APT gives 4km/px resolution, and Meteor LRPT gives much better 1km/px resolution but it is heavily compressed. Whereas HRPT gives peak resolutions of 1km/px uncompressed. There are also nine satellites in operation sending HRPT, so there are more opportunities to receive.
Derek has created a very comprehensive beginners guide that covers almost everything from purchasing and building the hardware, to finding and tracking the satellites, to setting up the software and decoding images. He notes that an RTL-SDR can be used as the receiver, and that a WiFi dish with GOES SAWBird LNA can work, although the difficult tracking requirements are still there so a smaller offset dish with custom helix feed might be preferred. Derek also provides useful tips, like the fact that the NOAA15 HRPT signal is quite a lot weaker than others.
Back in September 2020 we posted about the release of an X-Band decoder for the Elektro-L2 and Elektro-L3 Russian geostationary satellites. These satellites are receivable from Europe, the Middle East, Asia, Africa, South America and Australia. Unlike the HRIT and LRIT L-band transmissions from other geosynchronous satellites like GOES and GK-2A, the X-band Elektro signal is quite difficult to receive, requiring a large dish and more expensive hardware.
However we've recently seen exciting news on Twitter that a new L-band LRIT transmission has been activated on Elektro-L3. Like the Korean GK-2A satellite, this L-band LRIT transmission at 1691 MHz should be much easier to receive requiring only a WiFi dish, SAWBird GOES LNA and an RTL-SDR. We haven't yet confirmed if like GK-2A, the smaller 600 x 400 mm WiFi dish is sufficient, or if Elektro requires the larger 600 x 1000 mm dish size. (See our GOES satellite and GK-2A tutorial for information about the hardware being discussed in this paragraph.)
We note that the Elektro-L3 signal appears to be in testing, and the transmission could be turned on and off, or even turned off permanently. The transmission schedule is also not yet clear although in this recent tweet @HRPTEgor has mapped out some current transmission times for Eletro-L3.
It is hoped that LRIT will also eventually be activated on Elektro-L2, and perhaps even HRIT will be activated too. It is also exciting that more Elektro-L satellites are planned to be launched from 2022 onwards and we expect those to have hopefully LRIT and HRIT transmissions as well. To add further excitement, it is hoped that the L3 LRIT activation means that a LRIT or HRIT signal will be activated on the high elliptical orbit (HEO) northern hemisphere Arctic monitoring ARKTIKA-M1 satellite launched in Feb 2021, as this satellite is derived from the Elektro-L design.
The LRIT activation of Elektro-L3 hopefully means that Europeans should finally have access to a geostationary weather satellite that can be easily received with modest low cost hardware. The current coverage map from Orbitron of the two Elektro satellites is shown below (note that Elektro-L2 LRIT does not appear to have been activated yet).
Elektro-L2 and Elektro-L3 Coverage (Currently only Elektro-L3 LRIT transmissions have been discovered)
Over on Twitter @aang254 has noted that he has already updated his satdump software, adding support for Elektro LRIT decoding, and adding support for all of the available channels and for color. Satdump is available as a binary for Windows, and on Linux can be built from source. Experimentally, Satdump can also be built and run on Android.
The Tweet from @aang254 provides a nice sample image of what can be received.
I turns out ELEKTRO-L LRIT contains all 3 Visible channels and apparently 2 IR channels.
There are already many image decoders for the NOAA APT weather satellites available, with the most common and feature rich program being the abandoned freeware "WXtoIMG".
However many people may not know how simple the APT digital signal processing code is. Over on his blog post Dmitrii Eliuseev explains how only 50 lines of Python code are required to decode an image from received APT audio. Dmitrii's post shows how a Hilbert transform is used on the APT audio which is essentially the entire decoding step. This is then followed by a for loop that calculates the pixel luminosity from the decoded data, and plots it onto an image file.
Of course the image is only grayscale (or in Dmitrii's case he decided to use greenscale), but adding false color and various other image enhancements found in advanced software like WXtoIMG are just standard image processing techniques.
Dmitrii concludes with the following:
Interesting to mention, that there are not so many operational radio communication systems in the world, the signal of which can be decoded using 20 lines of code. The NOAA satellites are about 20 years old, and when they finally will retire, the new ones will most likely be digital and format will be much more complex (the new Russian Meteor-M2 satellite is already transmitting digital data at 137 MHz). So those who want to try something simple to decode can be advised to hurry up.
Over on GitHub stdevPavelmc has released his software called FAASGS (Fully Automatic Amateur Satellite Ground Station). FAASGS is an open source program that allows RTL-SDR users to set up a satellite ground station that tunes, record and generate images for NOAA APT weather satellites, as well as records FM amateur radio satellites. The software runs on a single board computer such as a Raspberry Pi, however in the authors own setup he uses an Orange Pi Prime board. The features include:
Web interface to see the next passes, the recorded ones, and details for it.
Receive any satellite in FM mode (SSB is possible but no there is doppler control yet, so no SSB by now)
Record the satellite pass and keep the audio for later.
APT WX audio is preserved in wav format and 22050 hz of sampling (the format wximage needs to work with)
FM audio satellites is preserved in .mp3 mode but with high quality settings, and other tricks.
The spectrogram of the audio is embedded as album art (see below).
The pass data and receiving station are stored in the mp3 tags.
Automatic decode APT images from WX sats (NOAA 15, 18 and 19)
For the voice FM sats we craft a spectrogram and embedd the metadata of the pass on the image
FAASGS main screen showing recordingsFAASGS screen showing an FM amateur radio satellite pass
Back in November 2020 we posted about the release of a decoder for the FengYun line of geostationary weather satellites which provide full disk images of the Earth and are positioned to cover parts of Europe, Africa, the Middle East, Asia, Russia, and Australia. Back then only a few people had attempted decoding this, and it was believed that a 120cm satellite dish or larger would be required.
We do note that u/Harrison_Clark55's image appears to be missing a few lines of data, and they are based in Australia where the elevation of FY-2G could be quite high depending on what side of the continent they are on. So it's possible that receivers in lower elevations may still require a larger dish size to work.
Full Disk FY-2G image received by u/Harrison_Clark55 (see the Reddit post for full resolution image)
Back in 2017 we posted about Adam 9A4QV's simple V-Dipole antenna design which works very well for receiving NOAA and Meteor weather satellites at 137 MHz. This type of antenna is a lot easier to build compared to a QFH or turnstile, and it results in good performance if built and set up correctly. Over the years he notes that he's received a number of questions asking to clarify the design and so he's uploaded a YouTube video which explains the built and dimensions of the antenna clearly.
